19-4023; Rev 0; 4/06 KIT ATION EVALU LE B A IL A AV High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers Applications ♦ 40/60 Optimal Interleaving ♦ Accurate Differential Current-Sense Inputs ♦ Internal 5V and 3.3V Linear Regulators with 100mA Load Capability ♦ Auxiliary 12V or Adjustable 150mA Linear Regulator (MAX1537A Only) ♦ Dual Mode™ Feedback—3.3V/5V Fixed or Adjustable Output (Dual Mode) Voltages ♦ 200kHz/300kHz/500kHz Switching Frequency ♦ Versatile Power-Up Sequencing ♦ Adjustable Overvoltage and Undervoltage Protection ♦ 6V to 26V Input Range ♦ 2V ±0.75% Reference Output ♦ Power-Good Output ♦ Soft-Shutdown ♦ 5µA (typ) Shutdown Current BST5 LX5 IN CSH5 CSL5 TOP VIEW DH5 Pin Configurations SKIP The MAX1533A/MAX1537A include on-board power-up sequencing, a power-good (PGOOD) output, digital soft-start, and internal soft-shutdown output discharge that prevents negative voltages on shutdown. The MAX1533A is available in a 32-pin 5mm x 5mm thin QFN package, and the MAX1537A is available in a 36pin 6mm x 6mm thin QFN package. The exposed backside pad improves thermal characteristics for demanding linear keep-alive applications. ♦ Fixed-Frequency, Current-Mode Control SHDN The MAX1533A/MAX1537A are dual step-down, switchmode power-supply (SMPS) controllers with synchronous rectification, intended for main 5V/3.3V power generation in battery-powered systems. Fixed-frequency operation with optimal interleaving minimizes input ripple current from the lowest input voltages up to the 26V maximum input. Optimal 40/60 interleaving allows the input voltage to go down to 8.3V before duty-cycle overlap occurs, compared to 180° out-of-phase regulators where the duty-cycle overlap occurs when the input drops below 10V. Output current sensing provides accurate current limit using a sense resistor. Alternatively, power dissipation can be reduced using lossless inductor current sensing. Internal 5V and 3.3V linear regulators power the MAX1533A/MAX1537A and their gate drivers, as well as external keep-alive loads, up to a total of 100mA. When the main PWM regulators are in regulation, automatic bootstrap switches bypass the internal linear regulators, providing currents up to 200mA from each linear output. An additional 5V to 23V adjustable internal 150mA linear regulator is typically used with a secondary winding to provide a 12V supply. Features 32 31 30 29 28 27 26 25 ON5 1 24 FB5 2 to 4 Li+ Cells Battery-Powered Devices ON3 2 23 LDO5 Notebook and Subnotebook Computers FSEL 3 22 DL5 PDAs and Mobile Communicators ILIM3 4 21 PGND 20 DL3 19 LDO3 MAX1537AETX -40°C to +85°C 36 Thin QFN 6mm x 6mm MAX1537AETX+ -40°C to +85°C 36 Thin QFN 6mm x 6mm +Denotes lead-free package. Dual Mode is a trademark of Maxim Integrated Products, Inc. FB3 17 CSL3 9 10 11 12 13 14 15 16 CSH3 -40°C to +85°C 32 Thin QFN 5mm x 5mm 18 8 OVP MAX1533AETJ+ 7 VCC LX3 -40°C to +85°C 32 Thin QFN 5mm x 5mm GND DH3 MAX1533AETJ 6 BST3 PIN-PACKAGE REF UVP TEMP RANGE 5 PGOOD PART ILIM5 PGDLY Ordering Information MAX1533A THIN QFN 5mm x 5mm Pin Configurations continued at end of data sheet. ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX1533A/MAX1537A General Description MAX1533A/MAX1537A High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers ABSOLUTE MAXIMUM RATINGS IN, SHDN, INA, LDOA to GND ...............................-0.3V to +30V GND to PGND .......................................................-0.3V to +0.3V LDO5, LDO3, VCC to GND .......................................-0.3V to +6V ILIM3, ILIM5, PGDLY to GND...................................-0.3V to +6V CSL3, CSH3, CSL5, CSH5 to GND ..........................-0.3V to +6V ON3, ON5, FB3, FB5 to GND ..................................-0.3V to +6V SKIP, OVP, UVP to GND...........................................-0.3V to +6V PGOOD, FSEL, ADJA, ONA to GND ........................-0.3V to +6V REF to GND ................................................-0.3V to (VCC + 0.3V) DL3, DL5 to PGND..................................-0.3V to (VLDO5 + 0.3V) BST3, BST5 to PGND .............................................-0.3V to +36V LX3 to BST3..............................................................-6V to +0.3V DH3 to LX3 ..............................................-0.3V to (VBST3 + 0.3V) LX5 to BST5..............................................................-6V to +0.3V DH5 to LX5 ..............................................-0.3V to (VBST5 + 0.3V) LDO3, LDO5 Short Circuit to GND .............................Momentary REF Short Circuit to GND ...........................................Momentary INA Shunt Current.............................................................+15mA Continuous Power Dissipation (TA = +70°C) 32-Pin TQFN (derate 21.3mW/°C above +70°C) .......1702mW 36-Pin TQFN (derate 26.3mW/°C above +70°C) .......2105mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (Circuit of Figure 1, VIN = 12V, both SMPS enabled, VCC = 5V, FSEL = REF, SKIP = GND, VILIM_ = VLDO5, VINA = 15V, VLDOA = 12V, ILDO5 = ILDO3 = ILDOA = no load, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS INPUT SUPPLIES (Note 1) VIN Input Voltage Range VIN VIN Operating Supply Current IIN LDO5 in regulation IN = LDO5, VOUT5 < 4.43V 6 26 4.5 5.5 V LDO5 switched over to CSL5 15 35 µA VIN Standby Supply Current IIN(STBY) VIN = 6V to 26V, both SMPS off, includes ISHDN 100 170 µA VIN Shutdown Supply Current IIN(SHDN) VIN = 6V to 26V, SHDN = GND 5 17 µA Quiescent Power Consumption PQ Both SMPS on, FB3 = FB5 = SKIP = GND, VCSL3 = 3.5V, VCSL5 = 5.3V, VINA = 15V, ILDOA = 0, PIN + PCSL3 + PCSL5 + PINA 3.5 4.5 mW VCC Quiescent Supply Current ICC Both SMPS on, FB3 = FB5 = GND, VCSL3 = 3.5V, VCSL5 = 5.3V 1.1 2.1 mA MAIN SMPS CONTROLLERS 3.3V Output Voltage in Fixed Mode VOUT3 VIN = 6V to 26V, SKIP = VCC (Note 2) 3.280 3.33 3.380 V 5V Output Voltage in Fixed Mode VOUT5 VIN = 6V to 26V, SKIP = VCC (Note 2) 4.975 5.05 5.125 V Feedback Voltage in Adjustable Mode VFB_ VIN = 6V to 26V, FB3 or FB5, duty factor = 20% to 80% (Note 2) 0.990 1.005 1.020 V Output-Voltage Adjust Range Either SMPS FB3, FB5 Dual-Mode Threshold Feedback Input Leakage Current VFB3 = VFB5 = 1.1V DC Load Regulation Either SMPS, SKIP = VCC, ILOAD = 0 to full load 2 1.0 5.5 V 0.1 0.2 V -0.1 +0.1 µA -0.1 _______________________________________________________________________________________ % High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers (Circuit of Figure 1, VIN = 12V, both SMPS enabled, VCC = 5V, FSEL = REF, SKIP = GND, VILIM_ = VLDO5, VINA = 15V, VLDOA = 12V, ILDO5 = ILDO3 = ILDOA = no load, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL Line-Regulation Error Operating Frequency (Note 1) Maximum Duty Factor (Note 1) Minimum On-Time CONDITIONS MIN TYP FSEL = GND 170 200 230 FSEL = REF 270 300 330 FSEL = VCC 425 500 575 FSEL = GND 91 93 Either SMPS, duty cycle = 10% to 90% fOSC DMAX tON(MIN) SMPS3 to SMPS5 Phase Shift MAX 1 FSEL = REF 91 93 FSEL = VCC 91 93 (Note 3) % kHz % 200 SMPS5 starts after SMPS3 UNITS ns 40 % 144 Deg CURRENT LIMIT ILIM_ Adjustment Range 0.5 VREF V Current-Sense Input Range CSH_, CSL_ 0 5.5 V Current-Sense Input Leakage Current CSH_, VCSH_ = 5.5V -1 +1 µA 70 75 80 mV Current-Limit Threshold (Fixed) VLIMIT_ VCSH_ - VCSL _, ILIM_ = VCC Current-Limit Threshold (Adjustable) VLIMIT_ VCSH_ - VCSL_ Current-Limit Threshold (Negative) Current-Limit Threshold (Zero Crossing) VNEG VZX VILIM_ = 2.00V 170 200 230 VILIM_ = 1.00V 91 100 109 VILIM_ = 0.50V 42 50 58 VCSH_ - VCSL_, SKIP = VCC, percent of current limit VPGND - VLX_, SKIP = GND, ILIM_ = VCC ILIM_ = VCC Idle-Mode™ Threshold VIDLE ILIM_ Leakage Current Soft-Start Ramp Time VCSH_ - VCSL _ With respect to currentlimit threshold (VLIMIT) ILIM3 = ILIM5 = GND or VCC tSS 10 -120 % 3 mV 16 22 20 -0.1 Measured from the rising edge of ON_ to full scale mV mV % +0.1 512 / fOSC µA s INTERNAL FIXED LINEAR REGULATORS ON3 = ON5 = GND, 6V < VIN < 26V, 0 < ILDO5 < 100mA 4.80 4.95 5.10 V LDO5 Undervoltage-Lockout Fault Threshold Rising edge, hysteresis = 1% 3.75 4.0 4.25 V LDO5 Bootstrap Switch Threshold Rising edge of CSL5, hysteresis = 1% 4.41 4.75 V LDO5 Bootstrap Switch Resistance LDO5 to CSL5, VCSL5 = 5V, ILDO5 = 50mA 3 Ω LDO5 Output Voltage VLDO5 0.75 Idle Mode is a trademark of Maxim Integrated Products, Inc. _______________________________________________________________________________________ 3 MAX1533A/MAX1537A ELECTRICAL CHARACTERISTICS (continued) MAX1533A/MAX1537A High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 1, VIN = 12V, both SMPS enabled, VCC = 5V, FSEL = REF, SKIP = GND, VILIM_ = VLDO5, VINA = 15V, VLDOA = 12V, ILDO5 = ILDO3 = ILDOA = no load, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER MIN TYP MAX UNITS Standby mode, 6V < VIN < 26V, 0 < ILOAD < 100mA 3.20 3.35 3.42 V LDO3 Bootstrap Switch Threshold Rising edge of CSL3, hysteresis = 1% 2.83 3.10 V LDO3 Bootstrap Switch Resistance LDO3 to CSL3, VCSL3 = 3.2V, ILDO3 = 50mA 1 3 Ω Short-Circuit Current LDO3 = LDO5 = GND, CSL3 = CSL5 = GND 150 220 mA Short-Circuit Current (Switched Over to CSL_) LDO3 = LDO5 = GND, VCSL3 > 3.1V, VCSL5 > 4.7V LDO3 Output Voltage SYMBOL VLDO3 CONDITIONS 250 mA AUXILIARY LINEAR REGULATOR (MAX1537A ONLY) LDOA Voltage Range INA Voltage Range VLDOA 5 23 V VINA 6 24 V LDOA Regulation Threshold, Internal Feedback ADJA = GND, 0 < ILDOA < 120mA, VINA > 13V 11.4 12.0 12.4 V 0 < ILDOA < 120mA, VLDOA > 5.0V and VINA > VLDOA + 1V 1.94 2.00 2.06 V 0.1 0.15 ADJA Leakage Current VADJA = 2.1V -0.1 LDOA Current Limit VLDOA forced to VINA - 1V, VADJA = 1.9V, VINA > 6V 150 Secondary Feedback Regulation Threshold VINA - VLDOA 0.65 DL Duty Factor VINA - VLDOA < 0.7V, pulse width with respect to switching period ADJA Regulation Threshold, External Feedback VADJA ADJA Dual-Mode Threshold INA Quiescent Current IINA INA Shunt Sink Current INA Leakage Current IINA(SHDN) V µA mA 0.8 0.95 33 VINA = 24V, ILDOA = no load VINA = 28V 0.2 +0.1 50 V % 165 10 µA mA VINA = 5V, LDOA disabled 30 µA 2.015 V 2.020 V REFERENCE (REF) Reference Voltage VREF Reference Load Regulation REF Lockout Voltage VCC = 4.5V to 5.5V, IREF = 0 1.985 IREF = -10µA to +100µA 1.980 VREF(UVLO) Rising edge, hysteresis = 350mV 2.00 1.95 V FAULT DETECTION OVP = GND, with respect to errorcomparator threshold Output Overvoltage Trip Threshold Output Overvoltage FaultPropagation Delay 4 tOVP 50mV overdrive 8 11 10 _______________________________________________________________________________________ 15 % µs High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers (Circuit of Figure 1, VIN = 12V, both SMPS enabled, VCC = 5V, FSEL = REF, SKIP = GND, VILIM_ = VLDO5, VINA = 15V, VLDOA = 12V, ILDO5 = ILDO3 = ILDOA = no load, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL Output Undervoltage-Protection Trip Threshold Output Undervoltage FaultPropagation Delay Output Undervoltage-Protection Blanking Time tUVP tBLANK TYP MAX UNITS With respect to error-comparator threshold 65 70 75 % 50mV overdrive From rising edge of ON_ tPGOOD_ Falling edge, 50mV overdrive IPGOOD_ High state, PGOOD forced to 5.5V PGOOD Output Low Voltage PGOOD Leakage Current MIN With respect to error-comparator threshold, hysteresis = 1% PGOOD Lower Trip Threshold PGOOD Propagation Delay CONDITIONS -14 µs 6144 / fOSC s -10 PGDLY = GND 4 PGDLY Pulldown Resistance REF0.2 PGDLY Trip Threshold TSHDN -7.5 10 ISINK = 4mA PGDLY Pullup Current Thermal-Shutdown Threshold 10 Hysteresis = 15°C % µs 0.4 V 1 µA 6 µA 10 25 Ω REF REF+ 0.2 V 5 °C +160 GATE DRIVERS DH_ Gate-Driver On-Resistance RDH DL_ Gate-Driver On-Resistance RDL DH_ Gate-Driver Source/Sink Current IDH DH_ forced to 2.5V, BST_ - LX_ forced to 5V DL_ Gate-Driver Source Current IDL IDL (SINK) DL_ Gate-Driver Sink Current Dead Time tDEAD LX_, BST_ Leakage Current BST_ - LX_ forced to 5V 1.5 5 DL_, high state 1.7 5 DL_, low state 0.6 3 Ω Ω 2 A DL_ forced to 2.5V 1.7 A DL_ forced to 2.5V 3.3 A DL_ rising 35 DH_ rising 26 VBST_ = VLX_ = 26V <2 ns 20 µA INPUTS AND OUTPUTS Logic Input Voltage SKIP, hysteresis = 600mV Fault Enable Logic Input Voltage OVP, UVP, ONA Logic Input Current OVP, UVP, SKIP, ONA High 2.4 Low High 0.8 0.7 x VCC V Low SHDN Input Trip Level 0.4 -1 +1 Rising trip level 1.10 1.6 2.20 Falling trip level 0.96 1 1.04 Clear fault level/SMPS off level ON_ Input Voltage V µA V 0.8 Delay start level (REF) 1.9 SMPS on level 2.4 2.1 V _______________________________________________________________________________________ 5 MAX1533A/MAX1537A ELECTRICAL CHARACTERISTICS (continued) MAX1533A/MAX1537A High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 1, VIN = 12V, both SMPS enabled, VCC = 5V, FSEL = REF, SKIP = GND, VILIM_ = VLDO5, VINA = 15V, VLDOA = 12V, ILDO5 = ILDO3 = ILDOA = no load, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS High FSEL Three-Level Input Logic MIN TYP REF 1.7 GND Input Leakage Current CSL_ Discharge-Mode On-Resistance MAX UNITS 2.3 V VCC - 0.2 0.4 OVP, UVP, SKIP, ONA, ON3, ON5 = GND or VCC -1 +1 SHDN, 0V or 26V -1 +1 FSEL = GND or VCC -3 +3 RDISCHARGE CSL_ Synchronous-Rectifier Discharge-Mode Turn-On Level 0.2 µA 10 25 Ω 0.3 0.4 V ELECTRICAL CHARACTERISTICS (Circuit of Figure 1, VIN = 12V, both SMPS enabled, VCC = 5V, FSEL = REF, SKIP = GND, VILIM_ = VLDO5, VINA = 15V, VLDOA = 12V, ILDO5 = ILDO3 = ILDOA = no load, TA = -40°C to +85°C, unless otherwise noted.) (Note 4) PARAMETER SYMBOL CONDITIONS MIN MAX UNITS INPUT SUPPLIES (Note 1) VIN Input Voltage Range VIN VIN Operating Supply Current IIN LDO5 in regulation IN = LDO5, VOUT5 < 4.4V 6 26 4.5 5.5 V LDO5 switched over to CSL5, either SMPS on 35 µA VIN Standby Supply Current IIN(STBY) VIN = 6V to 26V, both SMPS off, includes ISHDN 170 µA VIN Shutdown Supply Current IIN(SHDN) VIN = 6V to 26V 17 µA Quiescent Power Consumption PQ Both SMPS on, FB3 = FB5 = SKIP = GND, VCSL3 = 3.5V, VCSL5 = 5.3V, VINA = 15V, ILDOA = 0, PIN + PCSL3 + PCSL5 + PINA 4.5 mW VCC Quiescent Supply Current ICC Both SMPS on, FB3 = FB5 = GND, VCSL3 = 3.5V, VCSL5 = 5.3V 2.5 mA MAIN SMPS CONTROLLERS 3.3V Output Voltage in Fixed Mode VOUT3 VIN = 6V to 26V, SKIP = VCC (Note 2) 3.28 3.38 V 5V Output Voltage in Fixed Mode VOUT5 VIN = 6V to 26V, SKIP = VCC (Note 2) 4.975 5.125 V VIN = 6V to 26V, FB3 or FB5, duty factor = 20% to 80% (Note 2) 0.982 1.018 V Feedback Voltage in Adjustable Mode VFB3, VFB5 Output-Voltage Adjust Range Either SMPS 1.0 5.5 V FB3, FB5 Adjustable-Mode Threshold Voltage Dual-mode comparator 0.1 0.2 V 6 _______________________________________________________________________________________ High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers (Circuit of Figure 1, VIN = 12V, both SMPS enabled, VCC = 5V, FSEL = REF, SKIP = GND, VILIM_ = VLDO5, VINA = 15V, VLDOA = 12V, ILDO5 = ILDO3 = ILDOA = no load, TA = -40°C to +85°C, unless otherwise noted.) (Note 4) PARAMETER Operating Frequency (Note 1) Maximum Duty Factor (Note 1) Minimum On-Time SYMBOL fOSC DMAX MIN MAX FSEL = GND CONDITIONS 170 230 FSEL = REF 240 330 FSEL = VCC 375 575 FSEL = GND 91 FSEL = REF 91 FSEL = VCC 91 tON(MIN) UNITS kHz % 250 ns CURRENT LIMIT ILIM_ Adjustment Range Current-Limit Threshold (Fixed) Current-Limit Threshold (Adjustable) VLIMIT_ VLIMIT_ 0.5 VREF V 67 83 mV VILIM_ = 2.00V 170 230 VILIM_ = 1.00V 90 110 VILIM_ = 0.50V 40 60 ON3 = ON5 = GND, 6V < VIN < 26V, 0 < ILDO5 < 100mA 4.8 5.1 V Rising edge, hysteresis = 1% 3.75 4.30 V Standby mode, 6V < VIN < 28V, 0 < ILOAD < 100mA 3.20 3.43 V 5 23 V VCSH_ - VCSL _, ILIM_ = VCC VCSH_ - VCSL _ mV INTERNAL FIXED LINEAR REGULATORS LDO5 Output Voltage VLDO5 LDO5 Undervoltage-Lockout Fault Threshold LDO3 Output Voltage VLDO3 AUXILIARY LINEAR REGULATOR (MAX1537A ONLY) LDOA Voltage Range INA Voltage Range VLODA VINA 6 24 V ADJA = GND, 0 < ILDOA < 120mA, VINA > 13V 11.40 12.55 V 0 < ILDOA < 120mA, VLDOA > 5.0V and VINA > VLDOA + 1V 1.94 2.08 V ADJA Dual-Mode Threshold ADJA 0.10 0.25 V Secondary Feedback Regulation Threshold VINA - VLDOA 0.63 0.97 V 165 µA 2.03 V LDOA Regulation Threshold, Internal Feedback ADJA Regulation Threshold, External Feedback INA Quiescent Current VADJA IINA VINA = 24V, ILDOA = no load VREF VCC = 4.5V to 5.5V, IREF = 0 REFERENCE (REF) Reference Voltage 1.97 _______________________________________________________________________________________ 7 MAX1533A/MAX1537A ELECTRICAL CHARACTERISTICS (continued) MAX1533A/MAX1537A High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 1, VIN = 12V, both SMPS enabled, VCC = 5V, FSEL = REF, SKIP = GND, VILIM_ = VLDO5, VINA = 15V, VLDOA = 12V, ILDO5 = ILDO3 = ILDOA = no load, TA = -40°C to +85°C, unless otherwise noted.) (Note 4) PARAMETER SYMBOL CONDITIONS MIN MAX UNITS FAULT DETECTION Output Overvoltage Trip Threshold OVP = GND, with respect to errorcomparator threshold +8 +15 % Output Undervoltage-Protection Trip Threshold With respect to error-comparator threshold +65 +75 % PGOOD Lower Trip Threshold With respect to error-comparator threshold, hysteresis = 1% -14.0 -7.0 % PGOOD Output Low Voltage ISINK = 4mA 0.4 V 25 Ω REF+ 0.2 V BST_ - LX_ forced to 5V 5 Ω DL_, high state 5 DL_, low state 3 PGDLY Pulldown Resistance REF0.2 PGDLY Trip Threshold GATE DRIVERS DH_ Gate-Driver On-Resistance DL_ Gate-Driver On-Resistance RDH RDL Ω INPUTS AND OUTPUTS Logic Input Voltage SKIP, hysteresis = 600mV Fault Enable Logic Input Voltage OVP, UVP, ONA High 2.4 Low High 0.8 0.7 x VCC Low SHDN Input Trip Level ON_ Input Voltage 0.4 1.1 2.2 Falling trip level 0.95 1.05 Clear fault level 0.8 SMPS off level 1.6 SMPS on level FSEL Three-Level Input Logic V Rising trip level Delay start level (REF) V 1.9 2.1 V V 2.4 High VCC - 0.2 REF 1.7 GND 2.3 V 0.4 Note 1: The MAX1533A/MAX1537A cannot operate over all combinations of frequency, input voltage (VIN), and output voltage. For large input-to-output differentials and high-switching frequency settings, the required on-time may be too short to maintain the regulation specifications. Under these conditions, a lower operating frequency must be selected. The minimum on-time must be greater than 150ns, regardless of the selected switching frequency. On-time and off-time specifications are measured from 50% point to 50% point at the DH_ pin with LX_ = GND, VBST_ = 5V, and a 250pF capacitor connected from DH_ to LX_. Actual in-circuit times may differ due to MOSFET switching speeds. Note 2: When the inductor is in continuous conduction, the output voltage has a DC regulation level lower than the error-comparator threshold by 50% of the ripple. In discontinuous conduction (SKIP = GND, light load), the output voltage has a DC regulation level higher than the trip level by approximately 1% due to slope compensation. Note 3: Specifications are guaranteed by design, not production tested. Note 4: Specifications to -40°C are guaranteed by design, not production tested. 8 _______________________________________________________________________________________ High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers VIN = 7V 70 VIN = 12V VIN = 20V 60 0.01 0.1 MAX1533/37 toc02 4.96 10 5.04 5.00 4.96 4.92 SKIP = GND SKIP = VCC 4.88 0 1 2 3 4 5 6 5 10 15 20 25 LOAD CURRENT (A) INPUT VOLTAGE (V) PWM3 EFFICIENCY vs. LOAD CURRENT (VOUT3 = 3.3V) 3.3V OUTPUT VOLTAGE (OUT3) vs. LOAD CURRENT 3.3V OUTPUT VOLTAGE (OUT3) vs. INPUT VOLTAGE 70 VIN = 12V 3.33 3.30 3.27 NO LOAD 3.36 OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) VIN = 5V 80 SKIP = GND SKIP = VCC 3.36 3.39 MAX1533/37 toc05 MAX1533/37 toc04 3.39 30 MAX1533/37 toc06 LOAD CURRENT (A) 90 3.33 3.30 3.27 VIN = 20V 3.24 SKIP = GND SKIP = VCC 50 3.24 3.21 0.01 0.1 1 10 SKIP = GND SKIP = VCC 3.21 0 1 2 3 4 5 6 5 10 15 20 25 LOAD CURRENT (A) INPUT VOLTAGE (V) NO-LOAD SUPPLY CURRENT vs. INPUT VOLTAGE (FULLY ENABLED) NO-LOAD SUPPLY CURRENT vs. INPUT VOLTAGE (STANDBY MODE) SHUTDOWN SUPPLY CURRENT vs. INPUT VOLTAGE 28 24 20 SKIP = GND SKIP = VCC 16 12 8 4 1.0 ON3 = ON5 = GND 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.22mA (VIN = 12V) 0 5 10 15 20 INPUT VOLTAGE (V) SHDN = GND 8 30 6 4 2 0.1 0 0 10 SHUTDOWN SUPPLY CURRENT (μA) ON3 = ON5 = VCC STANDBY SUPPLY CURRENT (mA) 32 MAX1533/37 toc07 LOAD CURRENT (A) MAX1533/37 toc09 60 MAX1533/37 toc08 EFFICIENCY (%) 5.00 4.88 1 100 SUPPLY CURRENT (mA) 5.04 NO LOAD 5.08 4.92 SKIP = GND SKIP = VCC 50 5.12 OUTPUT VOLTAGE (V) 80 SKIP = GND SKIP = VCC 5.08 OUTPUT VOLTAGE (V) EFFICIENCY (%) 90 5V OUTPUT VOLTAGE (OUT5) vs. INPUT VOLTAGE 5.12 MAX1533 toc01 100 5V OUTPUT VOLTAGE (OUT5) vs. LOAD CURRENT MAX1533/37 toc03 PWM5 EFFICIENCY vs. LOAD CURRENT (VOUT5 = 5.0V) 25 30 0 0 5 10 15 20 INPUT VOLTAGE (V) 25 30 0 5 10 15 20 25 30 INPUT VOLTAGE (V) _______________________________________________________________________________________ 9 MAX1533A/MAX1537A Typical Operating Characteristics (MAX1537A circuit of Figure 1, VIN = 12V, LDO5 = VCC = 5V, SKIP = GND, FSEL = REF, TA = +25°C, unless otherwise noted.) Typical Operating Characteristics (continued) (MAX1537A circuit of Figure 1, VIN = 12V, LDO5 = VCC = 5V, SKIP = GND, FSEL = REF, TA = +25°C, unless otherwise noted.) 2.0 1.5 1.0 LDO DEVIATION VOLTAGE (mV) 2.5 50 MAX1533 toc11 DUTY CYCLE LIMITED 2.01 REF VOLTAGE (V) PEAK CURRENT (A) 2.02 MAX1533/37 toc10 3.5 3.0 LINEAR-REGULATOR LOAD REGULATION 2.0V REFERENCE LOAD REGULATION 2.00 1.99 0.5 MAX1533/37 toc12 IDLE-MODE CURRENT vs. INPUT VOLTAGE LDO3 0 LDO5 -50 -100 -150 VIN = 6V ON3 = ON5 = GND 5V OUTPUT 0 1.98 0 10 5 15 20 25 30 -200 -20 0 20 40 60 80 0 20 40 60 80 120 LDO LOAD CURRENT (mA) AUXILIARY LINEAR-REGULATOR LOAD REGULATION INTERLEAVED OPERATION LINEAR-REGULATOR STARTUP WAVEFORMS MAX1533/37 toc13 12.0 11.9 5V 12V 0 4V 5V B 0 C D 120 160 200 0 2V C 0 2V 3.3V E 0 F 11.7 80 B 2V 0 LDOA LOAD CURRENT (mA) A A 0 12V 40 140 MAX1533/37 toc15 MAX1533/37 toc14 0 100 REF LOAD CURRENT (μA) 11.8 10 100 INPUT VOLTAGE (V) 12.1 AUX LDO VOLTAGE (V) MAX1533A/MAX1537A High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers 2.0μs/div A. LX5, 10V/div B. 5V OUTPUT, 100mV/div C. PWM5 INDUCTOR CURRENT, 5A/div D. LX3, 10V/div E. 3.3V OUTPUT, 100mV/div F. PWM3 INDUCTOR CURRENT, 5A/div D 0 400μs/div A. SHDN, 5V/div B. LDO5, 2V/div C. LDO3, 2V/div D. REF, 2V/div 100Ω LOAD ON LDO5 AND LDO3 ______________________________________________________________________________________ High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers DELAYED STARTUP WAVEFORM (LIGHT LOAD) STARTUP WAVEFORM (HEAVY LOAD) 3.3V A 0 5V SHUTDOWN WAVEFORM (NO LOAD) MAX1533/37 toc17 MAX1533/37 toc16 3.3V 0 MAX1533/37 toc18 A 4V B 2V 0 3.3V C 0 B 0 5V C 0 3.3V 0 D 5V E 0 E F 0 2ms/div A. SHDN, 5V/div D. 3.3V OUTPUT, 5V/div B. 5V OUTPUT, 5V/div E. DL3, 5V/div C. DL5, 5V/div F. PGOOD, 5V/div ON3 = ON5 = VCC, OVP = GND 5V OUTPUT LOAD TRANSIENT (FORCED-PWM) MAX1533/37 toc19 2V 0 5V 5V D 0 A. ON5, 5V/div B. 5V OUTPUT, 2V/div C. INDUCTOR CURRENT, 5A/div D. LDO5, 1V/div E. DL5, 5V/div 1.0Ω LOAD SHUTDOWN WAVEFORM (1Ω LOAD) B 5V 400μs/div 2ms/div A. ON5, 5V/div B. 5V OUTPUT, 2V/div C. 3.3V OUPUT, 2V/div D. PGOOD, 2V/div 100Ω LOAD ON OUT5 AND OUT3, ON3 = REF A C 0 2.5A 0 D 0 2V 0 5V 3.3V OUTPUT LOAD TRANSIENT (FORCED-PWM) MAX1533/37 toc20 A 4A MAX1533/37 toc21 A 0 4A A 0 B B 5V B 3.3V C 5A D 0 4A 4A C 0 12V 5V 12V D E 0 0 100μs/div A. SHDN, 5V/div B. LDO5, 2V/div C. 5V OUTPUT, 2V/div D. INDUCTOR CURRENT, 5A/div E. DL5, 5V/div ON3 = ON5 = VCC, OVP = GND C 0 D 0 40μs/div A. IOUT5 = 0.2A TO 4A, 5A/div B. VOUT5 = 5.0V, 100mV/div C. INDUCTOR CURRENT, 5A/div D. LX5, 10V/div SKIP = VCC 40μs/div A. IOUT3 = 0.2A TO 4A, 5A/div B. VOUT3 = 3.3V, 100mV/div C. INDUCTOR CURRENT, 5A/div D. LX3, 10V/div SKIP = VCC ______________________________________________________________________________________ 11 MAX1533A/MAX1537A Typical Operating Characteristics (continued) (MAX1537A circuit of Figure 1, VIN = 12V, LDO5 = VCC = 5V, SKIP = GND, FSEL = REF, TA = +25°C, unless otherwise noted.) MAX1533A/MAX1537A High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers Typical Operating Characteristics (continued) (MAX1537A circuit of Figure 1, VIN = 12V, LDO5 = VCC = 5V, SKIP = GND, FSEL = REF, TA = +25°C, unless otherwise noted.) OUTPUT OVERLOAD (UVP ENABLED) 3.3V OUTPUT LOAD TRANSIENT (PULSE SKIPPING) 4A 5V A 0 MAX1533/37 toc24 A 0 3.3V 3.3V LDO5 LOAD TRANSIENT MAX1533/37 toc23 MAX1533/37 toc22 B B 0 30A B C 0 7A 0 C 12V D 0 A 0 100mA 4A 0 5V 12V 0 0 D 5.0V E 4.95V C 4μs/div 40μs/div A. PGOOD2, 5V/div B. 3.3V OUTPUT, 3.3V/div C. LOAD (0 TO 30A), 20A/div A. IOUT3 = 0.2A TO 4A, 5A/div B. VOUT3 = 3.3V, 100mV/div C. INDUCTOR CURRENT, 5A/div D. LX3, 10V/div SKIP = GND 20μs/div D. INDUCTOR CURRENT, 10A/div E. LX3, 20V/div A. CONTROL SIGNAL, 5V/div B. ILDO5 = 1mA TO 100mA, 100mA/div C. LDO5, 50m/div ON3 = ON5 = GND AUXILIARY LINEAR-REGULATOR LOAD TRANSIENT LDO5 LINE TRANSIENT MAX1533/37 toc25 MAX1533/37 toc26 20V 120mA 15V A A 10mA 10V 5V 14V 5.05V 13V 5.00V B 4.95V 11.96V C 11.90V 20μs/div A. INPUT VOLTAGE (VIN = 7V TO 20V), 5V/div B. LDO5 OUTPUT VOLTAGE, 50mV/div ON3 = ON5 = GND, ILDO5 = 20mA 12 B 100μs/div A. ILDOA = 10mA TO 100mA, 100mA/div B. INA, 1V/div C. LDOA, 50mV/div INA = VOLTAGE GENERATED BY SECONDARY TRANSFORMER WINDING ______________________________________________________________________________________ High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers PIN MAX1533A MAX1537A — 1 1 2 NAME FUNCTION ADJA Auxiliary Feedback Input. Connect a resistive voltage-divider from LDOA to analog ground to adjust the auxiliary linear-regulator output voltage. ADJA regulates at 2V. Connect ADJA to GND for nominal 12V output using internal feedback. ON5 5V SMPS Enable Input. The 5V SMPS is enabled if ON5 is greater than the SMPS on level and disabled if ON5 is less than the SMPS off level. If ON5 is connected to REF, the 5V SMPS starts after the 3.3V SMPS reaches regulation (delay start). Drive ON5 below the clear fault level to reset the fault latches. 2 3 ON3 3.3V SMPS Enable Input. The 3.3V SMPS is enabled if ON3 is greater than the SMPS on level and disabled if ON3 is less than the SMPS off level. If ON3 is connected to REF, the 3.3V SMPS starts after the 5V SMPS reaches regulation (delay start). Drive ON3 below the clear fault level to reset the fault latches. — 4 ONA LDOA Enable Input. When ONA is low, LDOA is high impedance and the secondary winding control is off. When ONA is high, LDOA is on. Connect to LDO3, LDO5, CSL3, CSL5, or other output for desired automatic startup sequencing. FSEL Frequency-Select Input. This three-level logic input sets the controller’s switching frequency. Connect to GND, REF, or VCC to select the following typical switching frequencies: VCC = 500kHz, REF = 300kHz, GND = 200kHz ILIM3 3.3V SMPS Peak Current-Limit Threshold Adjustment. The current-limit threshold defaults to 75mV if ILIM3 is connected to VCC. In adjustable mode, the current-limit threshold across CSH3 and CSL3 is precisely 1/10 the voltage seen at ILIM3 over a 500mV to 2.0V range. The logic threshold for switchover to the 75mV default value is approximately VCC - 1V. ILIM5 5V SMPS Peak Current-Limit Threshold. The current-limit threshold defaults to 75mV if ILIM5 is connected to VCC. In adjustable mode, the current-limit threshold across CSH5 and CSL5 is precisely 1/10th the voltage seen at ILIM5 over a 500mV to 2.0V range. The logic threshold for switchover to the 75mV default value is approximately VCC - 1V. 3 4 5 5 6 7 6 8 REF 2.0V Reference Voltage Output. Bypass REF to analog ground with a 0.1µF or greater ceramic capacitor. The reference can source up to 100µA for external loads. Loading REF degrades output-voltage accuracy according to the REF load-regulation error. The reference shuts down when SHDN is low. 7 9 GND Analog Ground. Connect the backside pad to GND. 8 10 VCC Analog Supply Input. Connect to the system supply voltage (+4.5V to +5.5V) through a series 20Ω resistor. Bypass VCC to analog ground with a 1µF or greater ceramic capacitor. PGDLY Power-Good One-Shot Delay. Place a timing capacitor on PGDLY to delay PGOOD going high. PGDLY has a 5µA pullup current and a 10Ω pulldown. The pulldown is activated when power is not good. When power is good, the pulldown is shut off and the 5µA pullup is activated. When PGDLY crosses REF, PGOOD is enabled. 9 11 ______________________________________________________________________________________ 13 MAX1533A/MAX1537A Pin Description MAX1533A/MAX1537A High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers Pin Description (continued) PIN MAX1533A 14 MAX1537A NAME FUNCTION Open-Drain Power-Good Output. PGOOD is low if either output is more than 10% (typ) below the normal regulation point, during soft-start, and in shutdown. PGOOD is delayed on the rising edge by the PGDLY one-shot timer. PGOOD becomes high impedance when both SMPS outputs are in regulation. 10 12 PGOOD 11 13 UVP Undervoltage Fault-Protection Control. Connect UVP to GND to select the default overvoltage threshold of 70% of nominal. Connect to VCC to disable undervoltage protection and clear the undervoltage fault latch. 12 14 DH3 High-Side Gate-Driver Output for 3.3V SMPS. DH3 swings from LX3 to BST3. 13 15 BST3 Boost Flying-Capacitor Connection for 3.3V SMPS. Connect to an external capacitor and diode as shown in Figure 6. An optional resistor in series with BST3 allows the DH3 pullup current to be adjusted. 14 16 LX3 Inductor Connection for 3.3V SMPS. Connect LX3 to the switched side of the inductor. LX3 serves as the lower supply rail for the DH3 high-side gate driver. 15 17 OVP Overvoltage Fault-Protection Control. Connect OVP to GND to select the default overvoltage threshold of +11% above nominal. Connect to VCC to disable overvoltage protection and clear the overvoltage fault latch. 16 18 CSH3 Positive Current-Sense Input for 3.3V SMPS. Connect to the positive terminal of the current-sense element. Figure 9 describes two different current-sensing options. 17 19 CSL3 Negative Current-Sense Input for 3.3V SMPS. Connect to the negative terminal of the current-sense element. Figure 9 describes two different current-sensing options. CSL3 also serves as the bootstrap input for LDO3. 18 20 FB3 Feedback Input for 3.3V SMPS. Connect to GND for fixed 3.3V output. In adjustable mode, FB3 regulates to 1V. 19 21 LDO3 20 22 DL3 21 23 PGND 22 24 DL5 23 25 LDO5 24 26 FB5 3.3V Internal Linear-Regulator Output. Bypass with 2.2µF (min) (1µF/20mA). Provides 100mA (min). Power is taken from LDO5. If CSL3 is greater than 3V, the linear regulator shuts down and LDO3 connects to CSL3 through a 1Ω switch rated for loads up to 200mA. Low-Side Gate-Driver Output for 3.3V SMPS. DL3 swings from PGND to LDO5. Power Ground Low-Side Gate-Driver Output for 5V SMPS. DL5 swings from PGND to LDO5. 5V Internal Linear-Regulator Output. Bypass with 2.2µF (min) (1µF/20mA). Provides power for the DL_ low-side gate drivers, the DH_ high-side drivers through the BST diodes, the PWM controller, logic, and reference through the VCC pin, as well as the LDO3 internal 3.3V linear regulator. Provides 100mA (min) for external loads (+25mA for gate drivers). If CSL5 is greater than 4.5V, the linear regulator shuts down and LDO5 connects to CSL5 through a 0.75Ω switch rated for loads up to 200mA. Feedback Input for 5V SMPS. Connect to GND for fixed 5V output. In adjustable mode, FB5 regulates to 1V. ______________________________________________________________________________________ High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers PIN NAME FUNCTION MAX1533A MAX1537A 25 27 CSL5 Negative Current-Sense Input for 5V SMPS. Connect to the negative terminal of the current-sense element. Figure 9 describes two different current-sensing options. CSL5 also serves as the bootstrap input for LDO5. 26 28 CSH5 Positive Current-Sense Input for 5V SMPS. Connect to the positive terminal of the current-sense element. Figure 9 describes two different current-sensing options. 27 29 IN 28 30 LX5 29 31 BST5 Boost Flying-Capacitor Connection for 5V SMPS. Connect to an external capacitor and diode as shown in Figure 6. An optional resistor in series with BST5 allows the DH5 pullup current to be adjusted. 30 32 DH5 High-Side Gate-Driver Output for 5V SMPS. DH5 swings from LX5 to BST5. 31 33 SKIP Pulse-Skipping Control Input. Connect to VCC for low-noise forced-PWM mode. Connect to GND for high-efficiency pulse-skipping mode at light loads. Input of the Startup Circuitry and the LDO5 Internal 5V Linear Regulator. Bypass to PGND with 0.22µF close to the IC. Inductor Connection for 5V SMPS. Connect LX5 to the switched side of the inductor. LX5 serves as the lower supply rail for the DH5 high-side gate driver. 32 34 SHDN Shutdown Control Input. The device enters its 5µA supply-current shutdown mode if VSHDN is less than the SHDN input falling-edge trip level and does not restart until VSHDN is greater than the SHDN input rising-edge trip level. Connect SHDN to VIN for automatic startup. SHDN can be connected to VIN through a resistive voltage-divider to implement a programmable undervoltage lockout. — 35 INA Supply Voltage Input for the Auxiliary LDOA Linear Regulator. INA is clamped with an internal shunt to 26V. LDOA Adjustable (12V Nominal) 150mA Auxiliary Linear-Regulator Output. Input supply comes from INA. Bypass LDOA to GND with 2.2µF (min) (1µF/20mA). Secondary feedback threshold is set at INA - LDOA = 0.8V, and triggers the DL5 on the 5V SMPS only. ONA high enables regulator output and secondary regulation. PGOOD is not affected by the state of LDOA. — 36 ______________________________________________________________________________________ 15 MAX1533A/MAX1537A Pin Description (continued) MAX1533A/MAX1537A High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers Table 1. Component Selection for Standard Applications COMPONENT 5A/300kHz 5A/500kHz Input Voltage VIN = 7V to 24V VIN = 7V to 24V (2) 10µF, 25V Taiyo Yuden TMK432BJ106KM (2) 10µF, 25V Taiyo Yuden TMK432BJ106KM COUT5, Output Capacitor 150µF, 6.3V, 40mΩ, low-ESR capacitor Sanyo 6TPB150ML 150µF, 6.3V, 40mΩ, low-ESR capacitor Sanyo 6TPB150ML COUT3, Output Capacitor 220µF, 4V, 40mΩ, low-ESR capacitor Sanyo 4TPB220ML 220µF, 4V, 40mΩ, low-ESR capacitor Sanyo 4TPB220ML NH_ High-Side MOSFET Fairchild Semiconductor FDS6612A International Rectifier IRF7807V Fairchild Semiconductor FDS6612A International Rectifier IRF7807V NL_ Low-Side MOSFET Fairchild Semiconductor FDS6670S International Rectifier IRF7807VD1 Fairchild Semiconductor FDS6670S International Rectifier IRF7807VD1 DL_ Schottky Rectifier (if needed) 2A, 30V, 0.45Vf Nihon EC21QS03L 2A, 30V, 0.45Vf Nihon EC21QS03L Inductor/Transformer T1 = 6.8µH, 1:2 turns Sumida 4749-T132 L1 = 5.8µH, 8.6A Sumida CDRH127-5R8NC 3.9µH Sumida CDRH124-3R9NC 10mΩ ±1%, 0.5W resistor IRC LR2010-01-R010F or Dale WSL-2010-R010F 10mΩ ±1%, 0.5W resistor IRC LR2010-01-R010F or Dale WSL-2010-R010F CIN_, Input Capacitor RCS Table 2. Component Suppliers SUPPLIER WEBSITE SUPPLIER WEBSITE AVX www.avx.com Panasonic www.panasonic.com/industrial Central Semiconductor www.centralsemi.com Sanyo www.secc.co.jp Coilcraft www.coilcraft.com Sumida www.sumida.com Coiltronics www.coiltronics.com Taiyo Yuden www.t-yuden.com Fairchild Semiconductor www.fairchildsemi.com TDK www.component.tdk.com International Rectifier www.irf.com TOKO www.tokoam.com Kemet www.kemet.com Vishay (Dale, Siliconix) www.vishay.com Detailed Description The MAX1533A/MAX1537A standard application circuit (Figure 1) generates the 5V/5A and 3.3V/5A typical of the main supplies in a notebook computer. The input supply range is 7V to 24V. See Table 1 for component selections and Table 2 for component manufacturers. The MAX1533A/MAX1537A contain two interleaved fixed-frequency step-down controllers designed for lowvoltage power supplies. The optimal interleaved architecture guarantees out-of-phase operation, reducing the input capacitor ripple. Two internal LDOs generate the keep-alive 5V and 3.3V power. The MAX1537A has an auxiliary LDO that can be configured to the preset 12V output or an adjustable output. 16 Fixed Linear Regulators (LDO5 and LDO3) Two internal linear regulators produce preset 5V (LDO5) and 3.3V (LDO3) low-power outputs. LDO5 powers LDO3, the gate drivers for the external MOSFETs, and provides the bias supply (VCC) required for the SMPS analog control, reference, and logic blocks. LDO5 supplies at least 100mA for external and internal loads, including the MOSFET gate drive, which typically varies from 5mA to 50mA, depending on the switching frequency and external MOSFETs selected. LDO3 also supplies at least 100mA for external loads. Bypass LDO5 and LDO3 with a 2.2µF or greater output capacitor, using an additional 1.0µF per 20mA of internal and external load. ______________________________________________________________________________________ High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers MAX1533A/MAX1537A INPUT (VIN) 5V LDO OUTPUT C1 10μF IN LDO5 DBST NH1 DL1 L1 5.8μH DBST DH3 CBST 0.1μF CIN (2) 10μF BST3 MAX1533A MAX1537A C5 22μF NH2 DH5 BST5 SECONDARY OUTPUT CBST 0.1μF LX3 LX5 DL3 DL5 NL1 D1 DL2 T1 1:2 TURNS LP = 6.8μH NL2 PGND GND RCS1 10mΩ 3.3V PWM OUTPUT COUT1 220μF 40mΩ CREF 0.22μF R3 60.4kΩ CSH3 CSH5 CSL3 CSL5 FB3 FB5 OVP UVP REF R2 100kΩ ON OFF REF (300kHz) R1 C2 1μF 20Ω ILIM5 PGOOD SHDN PGDLY ON3 ON OFF CONNECT TO LDO5 VCC R4 100kΩ R5 60.4kΩ 5V PWM OUTPUT COUT2 150μF 40mΩ SKIP FSEL ILIM3 RCS2 10mΩ R8 100kΩ POWER-GOOD 3.3V LDO OUTPUT LDO3 C3 10μF ON5 MAX1537A ONLY SECONDARY OUTPUT INA ON OFF ONA 12V LDO OUTPUT LDOA R6 OPEN C4 10μF ADJA R7 0Ω POWER GROUND SEE TABLE 1 FOR COMPONENT SPECIFICATIONS ANALOG GROUND Figure 1. MAX1533A/MAX1537A Standard Application Circuit ______________________________________________________________________________________ 17 MAX1533A/MAX1537A High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers SMPS to LDO Bootstrap Switchover When the 5V main output voltage is above the LDO5 bootstrap-switchover threshold, an internal 0.75Ω (typ) p-channel MOSFET shorts CSL5 to LDO5 while simultaneously shutting down the LDO5 linear regulator. Similarly, when the 3.3V main output voltage is above the LDO3 bootstrap-switchover threshold, an internal 1Ω (typ) p-channel MOSFET shorts CSL3 to LDO3 while simultaneously shutting down the LDO3 linear regulator. These actions bootstrap the device, powering the internal circuitry and external loads from the output SMPS voltages, rather than through linear regulators from the battery. Bootstrapping reduces power dissipation due to gate charge and quiescent losses by providing power from a 90%-efficient switch-mode source, rather than from a much-less-efficient linear regulator. The output current limit increases to 200mA when the LDO_ outputs are switched over. SMPS 5V Bias Supply (LDO5 and VCC) The A switch-mode power supplies (SMPS) require a 5V bias supply in addition to the high-power input supply (battery or AC adapter). This 5V bias supply is generated by the MAX1533A/MAX1537As’ internal 5V linear regulator (LDO5). This bootstrapped LDO allows the MAX1533A/MAX1537A to power-up independently. The gate-driver input supply is connected to the fixed 5V linear-regulator output (LDO5). Therefore, the 5V LDO supply must provide V CC (PWM controller) and the gate-drive power, so the maximum supply current required is: IBIAS = ICC + fSW (QG(LOW) + QG(HIGH)) = 5mA to 50mA (typ) where ICC is 1mA (typ), fSW is the switching frequency, and Q G(LOW) and Q G(HIGH) are the MOSFET data sheet’s total gate-charge specification limits at VGS = 5V. Reference (REF) The 2V reference is accurate to ±1% over temperature and load, making REF useful as a precision system reference. Bypass REF to GND with a 0.22µF or greater ceramic capacitor. The reference sources up to 100µA and sinks 10µA to support external loads. If highly accurate specifications (±0.5%) are required for the main SMPS output voltages, the reference should not be loaded. Loading the reference reduces the LDO5, LDO3, OUT5, and OUT3 output voltages slightly because of the reference load-regulation error. 18 System Enable/Shutdown (SHDN) Drive SHDN below the precise SHDN input falling-edge trip level to place the MAX1533A/MAX1537A in their low-power shutdown state. The MAX1533A/MAX1537A consume only 5µA of quiescent current while in shutdown mode. When shutdown mode activates, the reference turns off, making the threshold to exit shutdown less accurate. To guarantee startup, drive SHDN above 2.2V (SHDN input rising-edge trip level). For automatic shutdown and startup, connect SHDN to VIN. The accurate 1V falling-edge threshold on SHDN can be used to detect a specific input-voltage level and shut the device down. Once in shutdown, the 1.6V rising-edge threshold activates, providing sufficient hysteresis for most applications. SMPS Detailed Description SMPS POR, UVLO, and Soft-Start Power-on reset (POR) occurs when VCC rises above approximately 1V, resetting the undervoltage, overvoltage, and thermal-shutdown fault latches. The POR circuit also ensures that the low-side drivers are pulled low if OVP is disabled (OVP = VCC), or driven high if OVP is enabled (OVP = GND) until the SMPS controllers are activated. The VCC input undervoltage-lockout (UVLO) circuitry inhibits switching if the 5V bias supply (LDO5) is below the 4V input UVLO threshold. Once the 5V bias supply (LDO5) rises above this input UVLO threshold and the controllers are enabled, the SMPS controllers start switching and the output voltages begin to ramp up using soft-start. The internal digital soft-start gradually increases the internal current-limit level during startup to reduce the input surge currents. The MAX1533A/MAX1537A divide the soft-start period into five phases. During the first phase, each controller limits its current limit to only 20% of its full current limit. If the output does not reach regulation within 128 clock cycles (1 / fOSC), soft-start enters the second phase and the current limit is increased by another 20%. This process repeats until the maximum current limit is reached after 512 clock cycles (1 / fOSC) or when the output reaches the nominal regulation voltage, whichever occurs first (see the startup waveforms in the Typical Operating Characteristics). ______________________________________________________________________________________ High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers MAX1533A/MAX1537A LDO3 IN 5V LINEAR REGULATOR 3.3V LINEAR REGULATOR LDO5 SHDN LDO BYPASS CIRCUITRY OSC FSEL LDO BYPASS CIRCUITRY SKIP ILIM5 ILIM3 CSH5 CSH3 CSL5 BST5 CSL3 BST3 PWM5 CONTROLLER (FIGURE 3) PWM3 CONTROLLER (FIGURE 3) DH3 LX3 DH5 LX5 LDO5 LDO5 DL5 DL3 PGND FB3 FB DECODE (FIGURE 5) FB DECODE (FIGURE 5) FB5 INTERNAL FB ON5 ON3 REF OVP UVP POWER-GOOD AND FAULT PROTECTION (FIGURE 7) PGDLY PGOOD 2.0V REF SECONDARY FEEDBACK FAULT R R MAX1537A AUXILIARY LINEAR REGULATOR (FIGURE 8) VCC GND INA LDOA ADJA ONA MAX1533A/MAX1537A Figure 2. MAX1533A/MAX1537A Functional Diagram ______________________________________________________________________________________ 19 MAX1533A/MAX1537A High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers Table 3. Operating Modes MODE INPUTS* OUTPUTS SHDN ON5 ON3 LDO5 LDO3 5V SMPS 3V SMPS Shutdown Mode LOW X X OFF OFF OFF OFF Standby Mode HIGH LOW LOW ON ON OFF OFF Normal Operation HIGH HIGH HIGH ON ON ON ON 3.3V SMPS Active HIGH LOW HIGH ON ON OFF ON 5V SMPS Active HIGH HIGH LOW ON ON ON OFF ON ON Power-up after 3.3V SMPS is in regulation ON ON ON Power-up after 5V SMPS is in regulation Normal Operation (Delayed 5V SMPS Startup) Normal Operation (Delayed 3.3V SMPS Startup) HIGH HIGH REF HIGH HIGH REF ON ON ON *SHDN is an accurate, low-voltage logic input with 1V falling-edge threshold voltage and 1.6V rising-edge threshold voltage. ON3 and ON5 are 3-level CMOS logic inputs, a logic-low voltage is less than 0.8V, a logic-high voltage is greater than 2.4V, and the middle logic level is between 1.9V and 2.1V (see the Electrical Characteristics table). SMPS Enable Controls (ON3, ON5) ON3 and ON5 control SMPS power-up sequencing. ON3 or ON5 rising above 2.4V enables the respective outputs. ON3 or ON5 falling below 1.6V disables the respective outputs. Driving ON_ below 0.8V clears the overvoltage, undervoltage, and thermal fault latches. SMPS Power-Up Sequencing Connecting ON3 or ON5 to REF forces the respective outputs off while the other output is below regulation and starts after that output regulates. The second SMPS remains on until the first SMPS turns off, the device shuts down, a fault occurs, or LDO5 goes into undervoltage lockout. Both supplies begin their power-down sequence immediately when the first supply turns off. Output Discharge (Soft-Shutdown) When output discharge is enabled (OVP pulled low) and the switching regulators are disabled—by transitions into standby or shutdown mode, or when an output undervoltage fault occurs—the controller discharges both outputs through internal 12Ω switches, until the output voltages decrease to 0.3V. This slowly discharges the output capacitance, providing a softdamped shutdown response. This eliminates the slightly negative output voltages caused by quickly discharging the output through the inductor and lowside MOSFET. When an SMPS output discharges to 20 0.3V, its low-side driver (DL_) is forced high, clamping the respective SMPS output to GND. The reference remains active to provide an accurate threshold and to provide overvoltage protection. Both SMPS controllers contain separate soft-shutdown circuits. When output discharge is disabled (OVP = VCC), the lowside drivers (DL_) and high-side drivers (DH_) are both pulled low, forcing LX into a high-impedance state. Since the outputs are not actively discharged by the SMPS controllers, the output-voltage discharge rate is determined only by the output capacitance and load current. Fixed-Frequency, Current-Mode PWM Controller The heart of each current-mode PWM controller is a multiinput, open-loop comparator that sums two signals: the output-voltage error signal with respect to the reference voltage and the slope-compensation ramp (Figure 3). The MAX1533A/MAX1537A use a direct-summing configuration, approaching ideal cycle-to-cycle control over the output voltage without a traditional error amplifier and the phase shift associated with it. The MAX1533A/ MAX1537A use a relatively low loop gain, allowing the use of low-cost output capacitors. The low loop gain results in the -0.1% typical load-regulation error and helps reduce the output capacitor size and cost by shifting the unity-gain crossover frequency to a lower level. ______________________________________________________________________________________ High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers (SEE FIGURE 5) CSL REF / 2 SLOPE COMP AGND 0.2 x VLIMIT R Q IDLEMODE CURRENT S DH DRIVER SKIP SOFT-START COUNTER ON DAC CURRENT LIMIT OSC -1.2 x VLIMIT S R Q DL DRIVER LX PGND MAX1537A ONLY 0.8V ONE-SHOT SECONDARY FEEDBACK Figure 3: PWM-Controller Functional Diagram ______________________________________________________________________________________ 21 MAX1533A/MAX1537A FROM FB CSH MAX1533A/MAX1537A High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers Frequency Selection (FSEL) The FSEL input selects the PWM-mode switching frequency. Table 4 shows the switching frequency based on FSEL connection. High-frequency (500kHz) operation optimizes the application for the smallest component size, trading off efficiency due to higher switching losses. This may be acceptable in ultra-portable devices where the load currents are lower. Low-frequency (200kHz) operation offers the best overall efficiency at the expense of component size and board space. Forced-PWM Mode The low-noise forced-PWM mode disables the zerocrossing comparator, which controls the low-side switch on-time. This forces the low-side gate-drive waveform to constantly be the complement of the high-side gatedrive waveform, so the inductor current reverses at light loads while DH_ maintains a duty factor of VOUT / VIN. The benefit of forced-PWM mode is to keep the switching frequency fairly constant. However, forced-PWM operation comes at a cost: the no-load 5V supply current remains between 15mA and 50mA, depending on the external MOSFETs and switching frequency. Forced-PWM mode is most useful for avoiding audiofrequency noise and improving load-transient response. Since forced-PWM operation disables the zero-crossing comparator, the inductor current reverses under light loads. Light-Load Operation Control (SKIP) The MAX1533A/MAX1537A include a light-load operating-mode control input (SKIP) used to independently enable or disable the zero-crossing comparator for both controllers. When the zero-crossing comparator is enabled, the controller forces DL_ low when the current-sense inputs detect zero inductor current. This keeps the inductor from discharging the output capacitors and forces the controller to skip pulses under lightload conditions to avoid overcharging the output. When the zero-crossing comparator is disabled, the controller is forced to maintain PWM operation under light-load conditions (forced-PWM). Table 4. FSEL Configuration Table 22 FSEL SWITCHING FREQUENCY VCC 500kHz REF 300kHz GND 200kHz Idle-Mode Current-Sense Threshold The on-time of the step-down controller terminates when the output voltage exceeds the feedback threshold and when the current-sense voltage exceeds the idle-mode current-sense threshold. Under light-load conditions, the on-time duration depends solely on the idle-mode current-sense threshold, which is approximately 20% of the full-load current-limit threshold set by ILIM_. This forces the controller to source a minimum amount of power with each cycle. To avoid overcharging the output, another on-time cannot begin until the output voltage drops below the feedback threshold. Since the zero-crossing comparator prevents the switching regulator from sinking current, the controller must skip pulses. Therefore, the controller regulates the valley of the output ripple under light-load conditions. Automatic Pulse-Skipping Crossover In skip mode, an inherent automatic switchover to PFM takes place at light loads (Figure 4). This switchover is affected by a comparator that truncates the low-side switch on-time at the inductor current’s zero crossing. The zero-crossing comparator senses the inductor current across the low-side MOSFET (PGND to LX_). Once VPGND - VLX_ drops below the 3mV zero-crossing current-sense threshold, the comparator forces DL_ low (Figure 3). This mechanism causes the threshold between pulse-skipping PFM and nonskipping PWM operation to coincide with the boundary between continuous and discontinuous inductor-current operation (also known as the “critical conduction” point). The load-current level at which PFM/PWM crossover occurs, ILOAD(SKIP), is given by: ILOAD(SKIP) = VOUT (VIN − VOUT ) 2 × VIN × fSW × L The switching waveforms may appear noisy and asynchronous when light loading causes pulse-skipping operation, but this is a normal operating condition that results in high light-load efficiency. Trade-offs in PFM noise vs. light-load efficiency are made by varying the inductor value. Generally, low inductor values produce a broader efficiency vs. load curve, while higher values result in higher full-load efficiency (assuming that the coil resistance remains fixed) and less output voltage ripple. Penalties for using higher inductor values include larger physical size and degraded load-transient response (especially at low input-voltage levels). ______________________________________________________________________________________ High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers MAX1533A/MAX1537A TO ERROR AMPLIFIER ADJUSTABLE OUTPUT FB REF (2.0V) INDUCTOR CURRENT I L tON(SKIP) ≥ IDLE VIN - VOUT 12R R ILOAD(SKIP) FIXED OUTPUT FB = GND CSL 0 ON-TIME TIME Figure 4. Pulse-Skipping/Discontinuous Crossover Point Figure 5. Dual-Mode Feedback Decoder Output Voltage DC output accuracy specifications in the Electrical Characteristics table refer to the error-comparator’s threshold. When the inductor continuously conducts, the MAX1533A/MAX1537A regulate the peak of the output ripple, so the actual DC output voltage is lower than the slope-compensated trip level by 50% of the output ripple voltage. For PWM operation (continuous conduction), the output voltage is accurately defined by the following equation: ⎛ ASLOPE VNOM ⎞ ⎛ VRIPPLE ⎞ VOUT(PWM ) = VNOM ⎜1 ⎟ ⎟ - ⎜⎝ ⎠ VIN 2 ⎝ ⎠ where V NOM is the nominal output voltage, A SLOPE equals 1%, and VRIPPLE is the output ripple voltage (V RIPPLE = ESR x ΔI INDUCTOR as described in the Output Capacitor Selection section). In discontinuous conduction (IOUT < ILOAD(SKIP)), the MAX1533A/MAX1537A regulate the valley of the output ripple, so the output voltage has a DC regulation level higher than the error-comparator threshold. For PFM operation (discontinuous conduction), the output voltage is approximately defined by the following equation: VOUT(PFM ) = VNOM + 1 ⎛ fSW ⎞ IIDLE × ESR 2 ⎜⎝ fOSC ⎟⎠ where VNOM is the nominal output voltage, fOSC is the maximum switching frequency set by the internal oscillator, fSW is the actual switching frequency, and IIDLE is the idle-mode inductor current when pulse skipping. Adjustable/Fixed Output Voltages (Dual-Mode Feedback) Connect FB3 and FB5 to GND to enable the fixed SMPS output voltages (3.3V and 5V, respectively), set by a preset, internal resistive voltage-divider connected between CSL_ and analog ground. Connect a resistive voltage-divider at FB_ between CSL_ and GND to adjust the respective output voltage between 1V and 5.5V (Figure 5). Choose R2 (resistance from FB to GND) to be about 10kΩ and solve for R1 (resistance from OUT to FB) using the equation: ⎛ VOUT _ ⎞ R1 = R2 ⎜ − 1⎟ ⎝ VFB _ ⎠ where VFB_ = 1V nominal. ______________________________________________________________________________________ 23 MAX1533A/MAX1537A High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers When adjusting both output voltages, set the 3.3V SMPS lower than the 5V SMPS. LDO5 connects to the 5V output (CSL5) through an internal switch only when CSL5 is above the LDO5 bootstrap threshold (4.56V). Similarly, LDO3 connects to the 3.3V output (CSL3) through an internal switch only when CSL3 is above the LDO3 bootstrap threshold (2.91V). Bootstrapping works most effectively when the fixed output voltages are used. Once LDO_ is bootstrapped from CSL_, the internal linear regulator turns off. This reduces internal power dissipation and improves efficiency at higher input voltage. Current-Limit Protection (ILIM_) The current-limit circuit uses differential current-sense inputs (CSH_ and CSL_) to limit the peak inductor current. If the magnitude of the current-sense signal exceeds the current-limit threshold, the PWM controller turns off the high-side MOSFET (Figure 3). At the next rising edge of the internal oscillator, the PWM controller does not initiate a new cycle unless the current-sense signal drops below the current-limit threshold. The actual maximum load current is less than the peak current-limit threshold by an amount equal to half of the inductor ripple current. Therefore, the maximum load capability is a function of the current-sense resistance, inductor value, switching frequency, and duty cycle (VOUT / VIN). In forced-PWM mode, the MAX1533A/MAX1537A also implement a negative current limit to prevent excessive reverse inductor currents when VOUT is sinking current. The negative current-limit threshold is set to approximately 120% of the positive current limit and tracks the positive current limit when ILIM_ is adjusted. Connect ILIM_ to VCC for the 75mV default threshold, or adjust the current-limit threshold with an external resistor-divider at ILIM_. Use a 2µA to 20µA divider current for accuracy and noise immunity. The current-limit threshold adjustment range is from 50mV to 200mV. In the adjustable mode, the current-limit threshold voltage equals precisely 1/10th the voltage seen at ILIM_. The logic threshold for switchover to the 75mV default value is approximately VCC - 1V. Carefully observe the PC board layout guidelines to ensure that noise and DC errors do not corrupt the differential current-sense signals seen by CSH_ and CSL_. Place the IC close to the sense resistor with short, direct traces, making a Kelvin-sense connection to the current-sense resistor. 24 MOSFET Gate Drivers (DH_, DL_) The DH_ and DL_ drivers are optimized for driving moderate-sized high-side and larger low-side power MOSFETs. This is consistent with the low duty factor seen in notebook applications, where a large V IN V OUT differential exists. The high-side gate drivers (DH_) source and sink 2A, and the low-side gate drivers (DL_) source 1.7A and sink 3.3A. This ensures robust gate drive for high-current applications. The DH_ floating high-side MOSFET drivers are powered by diode-capacitor charge pumps at BST_ (Figure 6) while the DL_ synchronous-rectifier drivers are powered directly by the fixed 5V linear regulator (LDO5). Adaptive dead-time circuits monitor the DL_ and DH_ drivers and prevent either FET from turning on until the other is fully off. The adaptive driver dead time allows operation without shoot-through with a wide range of MOSFETs, minimizing delays and maintaining efficiency. There must be a low-resistance, low-inductance path from the DL_ and DH_ drivers to the MOSFET gates for the adaptive dead-time circuits to work properly; otherwise, the sense circuitry in the MAX1533A/ MAX1537A interprets the MOSFET gates as “off” while charge actually remains. Use very short, wide traces (50 to 100 mils wide if the MOSFET is 1 inch from the driver). The internal pulldown transistor that drives DL_ low is robust, with a 0.6Ω (typ) on-resistance. This helps prevent DL_ from being pulled up due to capacitive coupling from the drain to the gate of the low-side MOSFETs when the inductor node (LX_) quickly switches from ground to VIN. Applications with high input voltages and long inductive driver traces may require additional gate-to-source capacitance to ensure fastrising LX_ edges do not pull up the low-side MOSFETs’ gate, causing shoot-through currents. The capacitive coupling between LX_ and DL_ created by the MOSFET’s gate-to-drain capacitance (CRSS), gate-tosource capacitance (C ISS - C RSS ), and additional board parasitics should not exceed the following minimum threshold: ⎛C ⎞ VGS(TH) > VIN ⎜ RSS ⎟ ⎝ CISS ⎠ Lot-to-lot variation of the threshold voltage may cause problems in marginal designs. Alternatively, adding a resistor less than 10Ω in series with BST_ may remedy the problem by increasing the turn-on time of the highside MOSFET without degrading the turn-off time (Figure 6). ______________________________________________________________________________________ High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers CBYP MAX1533A MAX1537A LDO5 BST (RBST)* DBST INPUT (VIN) CBST DH NH L LX LDO5 DL NL (CNL)* GND Fault Protection Output Overvoltage Protection (OVP) If the output voltage of either SMPS rises above 111% of its nominal regulation voltage and the OVP protection is enabled (OVP = GND), the controller sets the fault latch, pulls PGOOD low, shuts down both SMPS controllers, and immediately pulls DH_ low and forces DL_ (RBST)* OPTIONAL—THE RESISTOR LOWERS EMI BY DECREASING THE SWITCHING-NODE RISE TIME. (CNL)* OPTIONAL—THE CAPACITOR REDUCES LX TO DL CAPACITIVE COUPLING THAT CAN CAUSE SHOOT-THROUGH CURRENTS. Figure 6. Optional Gate-Driver Circuitry FAULT PROTECTION POWER-GOOD 0.7 x INT REF_ 0.9 x INT REF_ 1.11 x INT REF_ INTERNAL FB ENABLE OVP ENABLE UVP BLANK (POWER-UP) TIMER POR FAULT LATCH FAULT POWERGOOD Figure 7. Power-Good and Fault Protection ______________________________________________________________________________________ 25 MAX1533A/MAX1537A Power-Good Output (PGOOD) PGOOD is the open-drain output of a comparator that continuously monitors both SMPS output voltages for undervoltage conditions. PGOOD is actively held low in shutdown (SHDN or ON3 or ON5 = GND), soft-start, and soft-shutdown. Once the digital soft-start terminates, PGOOD becomes high impedance as long as both outputs are above 90% of the nominal regulation voltage set by FB_. PGOOD goes low once either SMPS output drops 10% below its nominal regulation point, an output overvoltage fault occurs, or either SMPS controller is shut down. For a logic-level PGOOD output voltage, connect an external pullup resistor between PGOOD and VCC. A 100kΩ pullup resistor works well in most applications. PGOOD is independent of the fault protection states OVP and UVP. MAX1533A/MAX1537A High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers high. This turns on the synchronous-rectifier MOSFETs with 100% duty, rapidly discharging the output capacitors and clamping both outputs to ground. However, immediately latching DL_ high typically causes slightly negative output voltages due to the energy stored in the output LC at the instant the OVP occurs. If the load cannot tolerate a negative voltage, place a power Schottky diode across the output to act as a reversepolarity clamp. If the condition that caused the overvoltage persists (such as a shorted high-side MOSFET), the battery fuse blows. Cycle VCC below 1V or toggle either ON3, ON5, or SHDN to clear the fault latch and restart the SMPS controllers. Connect OVP to VCC to disable the output overvoltage protection. Output Undervoltage Protection (UVP) Each SMPS controller includes an output UVP protection circuit that begins to monitor the output 6144 clock cycles (1 / f OSC ) after that output is enabled (ON_ pulled high). If either SMPS output voltage drops below 70% of its nominal regulation voltage and the UVP protection is enabled (UVP = GND), the UVP circuit sets the fault latch, pulls PGOOD low, and shuts down both controllers using discharge mode (see the Output Discharge (Soft-Shutdown) section). When an SMPS output voltage drops to 0.3V, its synchronous rectifier turns on, clamping the discharged output to GND. Cycle V CC below 1V or toggle either ON3, ON5, or SHDN to clear the fault latch and restart the SMPS controllers. Connect UVP to VCC to disable the output undervoltage protection. Table 5. Operating Modes Truth Table MODE COMMENTS LDO5 < UVLO threshold. Transitions to discharge mode after VIN POR and after REF becomes valid. LDO5, LDO3, REF remain active. DL_ is active if OVP is low. SHDN = high, ON3 or ON5 enabled. Normal operation. Either output > 111% of nominal level, OVP = low. Exited by POR or cycling SHDN, ON3, or ON5. Either output < 70% of nominal level, UVP is enabled 6144 clock cycles (1 / fOSC) after the output is enabled and UVP = low. Exited by POR or cycling SHDN, ON3, or ON5. If OVP is not high, DL3 and DL5 go high after discharge. OVP is low and either SMPS output is still high in either standby mode or shutdown mode. Discharge switch (10Ω) connects CSL_ to PGND. This is a temporary state entered when LDO5 is undervoltage or on the way to output UVLO, standby, shutdown, or thermal-shutdown states. One SMPS can be in discharge mode while the other is in run mode. If both outputs are discharged to 0.3V (on CSL_), discharge mode transitions to the appropriate state. ON5 and ON3 < startup threshold, SHDN = high. DL_ stays high if OVP is low. LDO3, LDO5 active. Shutdown SHDN = low. All circuitry off. Thermal Shutdown TJ > +160°C. Exited by POR or cycling SHDN, ON3, or ON5. If OVP is not high, DL3 and DL5 go high before LDO5 turns off. Excessive current on LDO3 or LDO5 switchover transistors. Exited by POR or cycling SHDN, ON3, or ON5. If OVP is not high, DL3 and DL5 go high before LDO5 turns off. Power-Up Run Output Overvoltage Protection (OVP) Output Undervoltage Protection (UVP) Discharge Standby Switchover Fault 26 CONDITION ______________________________________________________________________________________ High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers Auxiliary LDO Detailed Description (MAX1537A Only) The MAX1537A includes an auxiliary linear regulator that delivers up to 150mA of load current. The output (LDOA) can be preset to 12V, ideal for PCMCIA power requirements, and for biasing the gates of load switches in a portable device. In adjustable mode, LDOA can be set to anywhere from 5V to 23V. The auxiliary regulator has an independent ON/OFF control, allowing it to be shut down when not needed, reducing power consumption when the system is in a low-power state. A flyback-winding control loop regulates a secondary winding output, improving cross-regulation when the primary output is lightly loaded or when there is a low input-output differential voltage. If VINA - VLDOA falls below 0.8V, the low-side switch is turned on for a time equal to 33% of the switching period. This reverses the inductor (primary) current, pulling current from the output filter capacitor and causing the flyback transformer to operate in forward mode. The low impedance presented by the transformer secondary in forward mode dumps current into the secondary output, charging up the secondary capacitor and bringing VINA - VLDOA back into regulation. The secondary feedback loop does not improve secondary output accuracy in normal flyback mode, where the main (primary) output is heavily loaded. In this condition, secondary output accuracy is determined by the secondary rectifier drop, transformer turns ratio, and accuracy of the main output voltage. Adjustable LDOA Voltage (Dual-Mode Feedback) Connect ADJA to GND to enable the fixed, preset 12V auxiliary output. Connect a resistive voltage-divider at ADJA between LDOA and GND to adjust the respective output voltage between 5V and 23V (Figure 8). Choose R2 (resistance from ADJA to GND) to be approximately SECONDARY FEEDBACK INA LDOA FIXED 12V ONA 5R REF (2.0V) R ADJA 0.15V Figure 8. Linear-Regulator Functional Diagram 100kΩ and solve for R1 (resistance from LDOA to ADJA) using the following equation: ⎛V ⎞ R1 = R2 ⎜ LDOA - 1⎟ ⎝ VADJA ⎠ where VADJA = 2V nominal. Design Procedure Firmly establish the input voltage range and maximum load current before choosing a switching frequency and inductor operating point (ripple-current ratio). The primary design trade-off lies in choosing a good switching frequency and inductor operating point, and the following four factors dictate the rest of the design: • Input Voltage Range. The maximum value (VIN(MAX)) must accommodate the worst-case, high AC-adapter voltage. The minimum value (VIN(MIN)) must account for the lowest battery voltage after drops due to connectors, fuses, and battery-selector switches. If there is a choice at all, lower input voltages result in better efficiency. ______________________________________________________________________________________ 27 MAX1533A/MAX1537A Thermal Fault Protection The MAX1533A/MAX1537A feature a thermal fault-protection circuit. When the junction temperature rises above +160°C, a thermal sensor activates the fault latch, pulls PGOOD low, and shuts down both SMPS controllers using discharge mode (see the Output Discharge (Soft-Shutdown) section). When an SMPS output voltage drops to 0.3V, its synchronous rectifier turns on, clamping the discharged output to GND. Cycle V CC below 1V or toggle either ON3, ON5, or SHDN to clear the fault latch and restart the controllers after the junction temperature cools by 15°C. MAX1533A/MAX1537A High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers • Maximum Load Current. There are two values to consider. The peak load current (ILOAD(MAX)) determines the instantaneous component stresses and filtering requirements and thus drives output-capacitor selection, inductor saturation rating, and the design of the current-limit circuit. The continuous load current (ILOAD) determines the thermal stresses and thus drives the selection of input capacitors, MOSFETs, and other critical heat-contributing components. • Switching Frequency. This choice determines the basic trade-off between size and efficiency. The optimal frequency is largely a function of maximum input voltage, due to MOSFET switching losses that are proportional to frequency and VIN2. The optimum frequency is also a moving target, due to rapid improvements in MOSFET technology that are making higher frequencies more practical. • Inductor Operating Point. This choice provides trade-offs between size vs. efficiency and transient response vs. output ripple. Low inductor values provide better transient response and smaller physical size, but also result in lower efficiency and higher output ripple due to increased ripple currents. The minimum practical inductor value is one that causes the circuit to operate at the edge of critical conduction (where the inductor current just touches zero with every cycle at maximum load). Inductor values lower than this grant no further size-reduction benefit. The optimum operating point is usually found between 20% and 50% ripple current. When pulse skipping (SKIP low and light loads), the inductor value also determines the load-current value at which PFM/PWM switchover occurs. Inductor Selection The switching frequency and inductor operating point determine the inductor value as follows: L = VOUT ( VIN - VOUT ) VIN fOSC ILOAD(MAX) LIR For example: ILOAD(MAX) = 5A, VIN = 12V, VOUT = 5V, fOSC = 300kHz, 30% ripple current or LIR = 0.3. L = 5V × (12V - 5V) 12V × 300kHz × 5A × 0.3 = 6.50μH Find a low-loss inductor with the lowest possible DC resistance that fits in the allotted dimensions. Most inductor manufacturers provide inductors in standard values, such as 1.0µH, 1.5µH, 2.2µH, 3.3µH, etc. Also 28 look for nonstandard values, which can provide a better compromise in LIR across the input voltage range. If using a swinging inductor (where the no-load inductance decreases linearly with increasing current), evaluate the LIR with properly scaled inductance values. For the selected inductance value, the actual peak-to-peak inductor ripple current (ΔIINDUCTOR) is defined by: ΔIINDUCTOR = VOUT ( VIN - VOUT ) VIN fOSC L Ferrite cores are often the best choice, although powdered iron is inexpensive and can work well at 200kHz. The core must be large enough not to saturate at the peak inductor current (IPEAK): IPEAK = ILOAD(MAX) + ΔIINDUCTOR 2 Transformer Design (For the MAX1537A Auxiliary Output) A coupled inductor or transformer can be substituted for the inductor in the 5V SMPS to create an auxiliary output (Figure 1). The MAX1537A is particularly well suited for such applications because the secondary feedback threshold automatically triggers DL5 even if the 5V output is lightly loaded. The power requirements of the auxiliary supply must be considered in the design of the main output. The transformer must be designed to deliver the required current in both the primary and the secondary outputs with the proper turns ratio and inductance. The power ratings of the synchronous-rectifier MOSFETs and the current limit in the MAX1537A must also be adjusted accordingly. Extremes of low input-output differentials, widely different output loading levels, and high turns ratios can further complicate the design due to parasitic transformer parameters such as interwinding capacitance, secondary resistance, and leakage inductance. Power from the main and secondary outputs is combined to get an equivalent current referred to the main output. Use this total current to determine the current limit (see the Setting the Current Limit section): ILOAD(MAX) = PTOTAL / VOUT5 where PTOTAL is the sum of the main and secondary outputs and ILOAD(MAX) is the maximum output current used to determine the primary inductance (see the Inductor Selection section). ______________________________________________________________________________________ High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers N= VSEC + VFWD VOUT5 + VRECT + VSENSE where V SEC is the minimum required rectified secondary voltage, VFWD is the forward drop across the secondary rectifier, VOUT5(MIN) is the minimum value of the main output voltage, and VRECT is the on-state voltage drop across the synchronous-rectifier MOSFET. The transformer secondary return is often connected to the main output voltage instead of ground to reduce the necessary turns ratio. In this case, subtract VOUT5 from the secondary voltage (V SEC - V OUT5 ) in the transformer turns-ratio equation above. The secondary diode in coupled-inductor applications must withstand flyback voltages greater than 60V. Common silicon rectifiers, such as the 1N4001, are also prohibited because they are too slow. Fast silicon rectifiers such as the MURS120 are the only choice. The flyback voltage across the rectifier is related to the VIN - VOUT difference, according to the transformer turns ratio: VFLYBACK = VSEC + (VIN - VOUT5) x N where N is the transformer turns ratio (secondary windings/primary windings), and VSEC is the maximum secondary DC output voltage. If the secondary winding is returned to VOUT5 instead of ground, subtract VOUT5 from V FLYBACK in the equation above. The diode’s reverse-breakdown voltage rating must also accommodate any ringing due to leakage inductance. The diode’s current rating should be at least twice the DC load current on the secondary output. Transient Response The inductor ripple current also impacts transientresponse performance, especially at low VIN - VOUT differentials. Low inductor values allow the inductor current to slew faster, replenishing charge removed from the output filter capacitors by a sudden load step. The total output voltage sag is the sum of the voltage sag while the inductor is ramping up, and the voltage sag before the next pulse can occur. VSAG = ( L ΔILOAD(MAX) ) 2 2COUT ( VIN × DMAX - VOUT ) ΔILOAD(MAX) ( T - ΔT ) COUT + where D MAX is the maximum duty factor (see the Electrical Characteristics table), T is the switching period (1 / fOSC), and ΔT equals VOUT / VIN x T when in PWM mode, or L x 0.2 x IMAX / (VIN - VOUT) when in skip mode. The amount of overshoot during a full-load to noload transient due to stored inductor energy can be calculated as: VSOAR = (ΔILOAD(MAX) ) 2 L 2COUT VOUT Setting the Current Limit The minimum current-limit threshold must be great enough to support the maximum load current when the current limit is at the minimum tolerance value. The peak inductor current occurs at ILOAD(MAX) plus half the ripple current; therefore: ⎛ ΔI ⎞ ILIMIT > ILOAD(MAX) + ⎜ INDUCTOR ⎟ ⎝ ⎠ 2 where ILIMIT equals the minimum current-limit threshold voltage divided by the current-sense resistance (RSENSE). For the default setting, the minimum currentlimit threshold is 70mV. Connect ILIM_ to V CC for the default current-limit threshold. In adjustable mode, the current-limit threshold is precisely 1/10th the voltage seen at ILIM_. For an adjustable threshold, connect a resistive divider from REF to analog ground (GND) with ILIM_ connected to the center tap. The external 500mV to 2V adjustment range corresponds to a 50mV to 200mV current-limit threshold. When adjusting the current limit, use 1% tolerance resistors and a divider current of approximately 10µA to prevent significant inaccuracy in the currentlimit tolerance. The current-sense method (Figure 9) and magnitude determine the achievable current-limit accuracy and power loss. Typically, higher current-sense limits provide tighter accuracy, but also dissipate more power. Most applications employ a current-limit threshold (VLIMIT) of 50mV to 100mV, so the sense resistor can be determined by: RSENSE = VLIMIT / ILIM For the best current-sense accuracy and overcurrent protection, use a 1% tolerance current-sense resistor between the inductor and output as shown in Figure ______________________________________________________________________________________ 29 MAX1533A/MAX1537A The transformer turns ratio (N) is determined by: MAX1533A/MAX1537A High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers 9a. This configuration constantly monitors the inductor current, allowing accurate current-limit protection. Alternatively, high-power applications that do not require highly accurate current-limit protection may reduce the overall power dissipation by connecting a series RC circuit across the inductor (Figure 9b) with an equivalent time constant: where RL is the inductor’s series DC resistance. In this configuration, the current-sense resistance equals the inductor’s DC resistance (RSENSE = RL). Use the worstcase inductance and RL values provided by the inductor manufacturer, adding some margin for the inductance drop over temperature and load. Output Capacitor Selection The output filter capacitor must have low enough equivalent series resistance (ESR) to meet output ripple and load-transient requirements, yet have high enough ESR to satisfy stability requirements. The output capacitance must be high enough to absorb the inductor L = CEQ × REQ RL INPUT (VIN) DH_ NH CIN RSENSE L LX_ MAX1533A DL_ MAX1537A NL COUT DL GND CSH_ CSL_ a) OUTPUT SERIES RESISTOR SENSING INPUT (VIN) DH_ NH CIN NL DL INDUCTOR LX_ MAX1533A DL_ MAX1537A COUT GND REQ CEQ CSH_ CSL_ b) LOSSLESS INDUCTOR SENSING Figure 9. Current-Sense Configurations 30 ______________________________________________________________________________________ High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers VRIPPLE(P − P) = RESR ILOAD(MAX) LIR In idle mode, the inductor current becomes discontinuous, with peak currents set by the idle-mode currentsense threshold (VIDLE = 0.2VLIMIT). In idle mode, the no-load output ripple can be determined as follows: VRIPPLE(P − P) = VIDLE RESR RSENSE The actual capacitance value required relates to the physical size needed to achieve low ESR, as well as to the chemistry of the capacitor technology. Thus, the capacitor is usually selected by ESR and voltage rating rather than by capacitance value (this is true of tantalums, OS-CONs, polymers, and other electrolytics). When using low-capacity filter capacitors, such as ceramic capacitors, size is usually determined by the capacity needed to prevent V SAG and V SOAR from causing problems during load transients. Generally, once enough capacitance is added to meet the overshoot requirement, undershoot at the rising load edge is no longer a problem (see the VSAG and VSOAR equations in the Transient Response section). However, lowcapacity filter capacitors typically have high-ESR zeros that may affect the overall stability (see the OutputCapacitor Stability Considerations). Output-Capacitor Stability Considerations Stability is determined by the value of the ESR zero relative to the switching frequency. The boundary of instability is given by the following equation: fESR ≤ where fESR = fOSC π 1 2π RESR COUT For a typical 300kHz application, the ESR zero frequency must be well below 95kHz, preferably below 50kHz. Tantalum and OS-CON capacitors in widespread use at the time of publication have typical ESR zero frequencies of 25kHz. In the design example used for inductor selection, the ESR needed to support 25mVP-P ripple is 25mV / 1.5A = 16.7mΩ. One 220µF/4V Sanyo polymer (TPE) capacitor provides 15mΩ (max) ESR. This results in a zero at 48kHz, well within the bounds of stability. For low-input-voltage applications where the duty cycle exceeds 50% (VOUT / VIN ≥ 50%), the output ripple voltage should not be greater than twice the internal slopecompensation voltage: VRIPPLE ≤ 0.02 x VOUT where VRIPPLE equals ΔIINDUCTOR x RESR. The worstcase ESR limit occurs when VIN = 2 x VOUT, so the above equation can be simplified to provide the following boundary condition: RESR ≤ 0.04 x L x fOSC Do not put high-value ceramic capacitors directly across the feedback sense point without taking precautions to ensure stability. Large ceramic capacitors can have a high-ESR zero frequency and cause erratic, unstable operation. However, it is easy to add enough series resistance by placing the capacitors a couple of inches downstream from the feedback sense point, which should be as close as possible to the inductor. Unstable operation manifests itself in two related but distinctly different ways: short/long pulses or cycle skipping resulting in a lower switching frequency. Instability occurs due to noise on the output or because the ESR is so low that there is not enough voltage ramp in the output voltage signal. This “fools” the error comparator into triggering too early or skipping a cycle. Cycle skipping is more annoying than harmful, resulting in nothing worse than increased output ripple. However, it can indicate the possible presence of loop instability due to insufficient ESR. Loop instability can result in oscillations at the output after line or load steps. Such perturbations are usually damped, but can cause the output voltage to rise above or fall below the tolerance limits. The easiest method for checking stability is to apply a very fast zero-to-max load transient and carefully observe the output-voltage-ripple envelope for overshoot and ringing. It can help to simultaneously monitor the inductor current with an AC-current probe. Do not allow more than one cycle of ringing after the initial step-response under/overshoot. Input Capacitor Selection The input capacitor must meet the ripple current requirement (IRMS) imposed by the switching currents. For an out-of-phase regulator, the total RMS current in the input capacitor is a function of the load currents, the input currents, the duty cycles, and the amount of overlap as defined in Figure 10. ______________________________________________________________________________________ 31 MAX1533A/MAX1537A energy while transitioning from full-load to no-load conditions without tripping the overvoltage fault protection. When using high-capacitance, low-ESR capacitors (see the Output-Capacitor Stability Considerations section), the filter capacitor’s ESR dominates the output voltage ripple. So the output capacitor’s size depends on the maximum ESR required to meet the output voltage ripple (VRIPPLE(P-P)) specifications: The 40/60 optimal interleaved architecture of the MAX1533A/MAX1537A allows the input voltage to go as low as 8.3V before the duty cycles begin to overlap. This offers improved efficiency over a regular 180° outof-phase architecture where the duty cycles begin to overlap below 10V. Figure 10 shows the input-capacitor RMS current vs. input voltage for an application that requires 5V/5A and 3.3V/5A. This shows the improvement of the 40/60 optimal interleaving over 50/50 interleaving and in-phase operation. For most applications, nontantalum chemistries (ceramic, aluminum, or OS-CON) are preferred due to their resistance to power-up surge currents typical of systems with a mechanical switch or connector in series with the input. Choose a capacitor that has less than 10°C temperature rise at the RMS input current for optimal reliability and lifetime. Power-MOSFET Selection Most of the following MOSFET guidelines focus on the challenge of obtaining high load-current capability when using high-voltage (>20V) AC adapters. Low-current applications usually require less attention. The high-side MOSFET (NH) must be able to dissipate the resistive losses plus the switching losses at both INPUT CAPACITOR RMS CURRENT vs. INPUT VOLTAGE 5.0 VIN(MIN) and VIN(MAX). Ideally, the losses at VIN(MIN) should be roughly equal to the losses at VIN(MAX), with lower losses in between. If the losses at VIN(MIN) are significantly higher, consider increasing the size of NH. Conversely, if the losses at VIN(MAX) are significantly higher, consider reducing the size of NH. If VIN does not vary over a wide range, maximum efficiency is achieved by selecting a high-side MOSFET (NH) that has conduction losses equal to the switching losses. Choose a low-side MOSFET (NL) that has the lowest possible on-resistance (RDS(ON)), comes in a moderate-sized package (i.e., SO-8, DPAK, or D2PAK), and is reasonably priced. Ensure that the MAX1533A/ MAX1537A DL_ gate driver can supply sufficient current to support the gate charge and the current injected into the parasitic drain-to-gate capacitor caused by the high-side MOSFET turning on; otherwise, crossconduction problems may occur. Switching losses are not an issue for the low-side MOSFET since it is a zerovoltage switched device when used in the step-down topology. Power-MOSFET Dissipation Worst-case conduction losses occur at the duty factor extremes. For the high-side MOSFET (NH), the worstcase power dissipation due to resistance occurs at minimum input voltage: ⎛V ⎞ 2 PD (NH Re sistive) = ⎜ OUT ⎟ (ILOAD ) RDS(ON) ⎝ VIN ⎠ 4.5 4.0 IN PHASE 3.5 IRMS (A) MAX1533A/MAX1537A High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers 50/50 INTERLEAVING 3.0 2.5 2.0 1.5 40/60 OPTIMAL INTERLEAVING 1.0 0.5 5V/5A AND 3.3V/5A 0 6 8 10 12 14 16 18 20 VIN (V) INPUT RMS CURRENT FOR INTERLEAVED OPERATION IRMS = (IOUT5 - IIN)2 (DLX5 - DOL) + (IOUT3 - IIN)2 (DLX3 - DOL) + (IOUT5 + IOUT3 - IIN)2 DOL + IIN2 (1 - DLX5 - DLX3 + DOL) V DLX5 = OUT5 VIN V DLX3 = OUT3 VIN DOL = DUTY-CYCLE OVERLAP FRACTION INPUT RMS CURRENT FOR SINGLE-PHASE OPERATION ( IRMS = ILOAD VOUT (VIN - VOUT) VIN Figure 10. Input RMS Current 32 ) Generally, use a small high-side MOSFET to reduce switching losses at high input voltages. However, the RDS(ON) required to stay within package power-dissipation limits often limits how small the MOSFET can be. The optimum occurs when the switching losses equal the conduction (RDS(ON)) losses. High-side switching losses do not become an issue until the input is greater than approximately 15V. Calculating the power dissipation in high-side MOSFETs (NH) due to switching losses is difficult, since it must allow for difficult-to-quantify factors that influence the turn-on and turn-off times. These factors include the internal gate resistance, gate charge, threshold voltage, source inductance, and PC board layout characteristics. The following switching loss calculation provides only a very rough estimate and is no substitute for breadboard evaluation, preferably including verification using a thermocouple mounted on NH: PD (NH (VIN(MAX) ) Switching) = 2 CRSS fSW ILOAD IGATE ______________________________________________________________________________________ High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers Switching losses in the high-side MOSFET can become a heat problem when maximum AC-adapter voltages are applied, due to the squared term in the switchingloss equation (C x VIN2 x fSW). If the high-side MOSFET chosen for adequate RDS(ON) at low battery voltages becomes extraordinarily hot when subjected to V IN(MAX) , consider choosing another MOSFET with lower parasitic capacitance. For the low-side MOSFET (NL), the worst-case power dissipation always occurs at maximum battery voltage: ⎡ ⎛ V ⎞⎤ 2 PD (NL Re sistive) = ⎢1 - ⎜ OUT ⎟ ⎥(ILOAD ) RDS(ON) ⎢ ⎝ VIN(MAX) ⎠ ⎥⎦ ⎣ CBST = QGATE 200mV where QGATE is the total gate charge specified in the high-side MOSFET’s data sheet. For example, assume the FDS6612A n-channel MOSFET is used on the high side. According to the manufacturer’s data sheet, a single FDS6612A has a maximum gate charge of 13nC (VGS = 5V). Using the above equation, the required boost capacitance is: CBST = 13nC = 0.065μF 200mV Selecting the closest standard value. This example requires a 0.1µF ceramic capacitor. Applications Information The absolute worst case for MOSFET power dissipation occurs under heavy-overload conditions that are greater than ILOAD(MAX) but are not high enough to exceed the current limit and cause the fault latch to trip. To protect against this possibility, “overdesign” the circuit to tolerate: ⎛ ΔI ⎞ ILOAD = ILIMIT - ⎜ INDUCTOR ⎟ ⎝ ⎠ 2 where ILIMIT is the peak current allowed by the currentlimit circuit, including threshold tolerance and senseresistance variation. The MOSFETs must have a relatively large heatsink to handle the overload power dissipation. Choose a Schottky diode (DL) with a forward-voltage drop low enough to prevent the low-side MOSFET’s body diode from turning on during the dead time. As a general rule, select a diode with a DC current rating equal to 1/3rd the load current. This diode is optional and can be removed if efficiency is not critical. Duty-Cycle Limits Minimum Input Voltage The minimum input operating voltage (dropout voltage) is restricted by the maximum duty-cycle specification (see the Electrical Characteristics table). However, keep in mind that the transient performance gets worse as the step-down regulators approach the dropout voltage, so bulk output capacitance must be added (see the voltage sag and soar equations in the Design Procedure section). The absolute point of dropout occurs when the inductor current ramps down during the off-time (ΔIDOWN) as much as it ramps up during the on-time (ΔIUP). This results in a minimum operating voltage defined by the following equation: ⎛ 1 ⎞ - 1⎟ ( VOUT + VDIS ) VIN(MIN) = VOUT + VCHG + h ⎜ ⎝ DMAX ⎠ Boost Capacitors where VCHG and VDIS are the parasitic voltage drops in the charge and discharge paths, respectively. A reasonable minimum value for h is 1.5, while the absolute minimum input voltage is calculated with h = 1. The boost capacitors (CBST) must be selected large enough to handle the gate-charging requirements of the high-side MOSFETs. Typically, 0.1µF ceramic capacitors work well for low-power applications driving medium-sized MOSFETs. However, high-current applications driving large, high-side MOSFETs require boost capacitors larger than 0.1µF. For these applications, select the boost capacitors to avoid discharging the capacitor more than 200mV while charging the highside MOSFETs’ gates: Maximum Input Voltage The MAX1533A/MAX1537A controllers include a minimum on-time specification, which determines the maximum input operating voltage that maintains the selected switching frequency (see the Electrical Characteristics table). Operation above this maximum input voltage results in pulse-skipping operation, regardless of the operating mode selected by SKIP. At the beginning of each cycle, if the output voltage is still ______________________________________________________________________________________ 33 MAX1533A/MAX1537A where CRSS is the reverse transfer capacitance of NH, and IGATE is the peak gate-drive source/sink current (1A typ). MAX1533A/MAX1537A High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers above the feedback-threshold voltage, the controller does not trigger an on-time pulse, effectively skipping a cycle. This allows the controller to maintain regulation above the maximum input voltage, but forces the controller to effectively operate with a lower switching frequency. This results in an input threshold voltage at which the controller begins to skip pulses (VIN(SKIP)): ⎛ ⎞ 1 VIN(SKIP) = VOUT ⎜ ⎟ ⎝ fOSC t ON(MIN) ⎠ where fOSC is the switching frequency selected by FSEL. PC Board Layout Guidelines Careful PC board layout is critical to achieving low switching losses and clean, stable operation. The switching power stage requires particular attention (Figure 11). If possible, mount all of the power components on the top side of the board, with their ground terminals flush against one another. Follow these guidelines for good PC board layout: • Keep the high-current paths short, especially at the ground terminals. This practice is essential for stable, jitter-free operation. • Keep the power traces and load connections short. This practice is essential for high efficiency. Using thick copper PC boards (2oz vs. 1oz) can enhance full-load efficiency by 1% or more. Correctly routing PC board traces is a difficult task that must be approached in terms of fractions of centimeters, where a single mΩ of excess trace resistance causes a measurable efficiency penalty. • Minimize current-sensing errors by connecting CSH_ and CSL_ directly across the current-sense resistor (RSENSE_). 34 • When trade-offs in trace lengths must be made, it is preferable to allow the inductor charging path to be made longer than the discharge path. For example, it is better to allow some extra distance between the input capacitors and the high-side MOSFET than to allow distance between the inductor and the lowside MOSFET or between the inductor and the output filter capacitor. • Route high-speed switching nodes (BST_, LX_, DH_, and DL_) away from sensitive analog areas (REF, FB_, CSH_, CSL_). Layout Procedure 1) Place the power components first, with ground terminals adjacent (NL _ source, CIN, COUT_, and DL _ anode). If possible, make all these connections on the top layer with wide, copper-filled areas. 2) Mount the controller IC adjacent to the low-side MOSFET, preferably on the back side opposite NL_ and NH_ to keep LX_, GND, DH_, and the DL_ gatedrive lines short and wide. The DL_ and DH_ gate traces must be short and wide (50 to 100 mils wide if the MOSFET is 1 inch from the controller IC) to keep the driver impedance low and for proper adaptive dead-time sensing. 3) Group the gate-drive components (BST_ diode and capacitor, LDO5 bypass capacitor) together near the controller IC. 4) Make the DC-DC controller ground connections as shown in Figures 1 and 11. This diagram can be viewed as having two separate ground planes: power ground, where all the high-power components go; and an analog ground plane for sensitive analog components. The analog ground plane and power ground plane must meet only at a single point directly at the IC. 5) Connect the output power planes directly to the output-filter-capacitor positive and negative terminals with multiple vias. Place the entire DC-DC converter circuit as close to the load as is practical. ______________________________________________________________________________________ High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers MAX1533A/MAX1537A CONNECT GND AND PGND TO THE CONTROLLER AT ONE POINT ONLY AS SHOWN CONNECT THE EXPOSED PAD TO ANALOG GND VIA TO POWER GROUND VIA TO REF BYPASS CAPACITOR VIA TO REF PIN VIA TO VCC BYPASS CAPACITOR MAX1533A TOP LAYER MAX1533A BOTTOM LAYER KELVIN-SENSE VIAS UNDER THE SENSE RESISTOR (SEE THE EVALUATION KIT) VIA TO VCC PIN DUAL n-CHANNEL MOSFET INDUCTOR SINGLE n-CHANNEL MOSFETS INDUCTOR DH LX DL COUT CIN COUT CIN INPUT HIGH-POWER LAYOUT INPUT OUTPUT COUT OUTPUT GROUND GROUND LOW-POWER LAYOUT Figure 11. PC Board Layout ______________________________________________________________________________________ 35 High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers TRANSISTOR COUNT: 6890 PROCESS: BiCMOS CSL5 FB5 ADJA ON5 1 27 2 26 ON3 ONA 3 25 4 24 FSEL ILIM3 5 ILIM5 REF GND 7 21 8 20 PGND DL3 LDO3 FB3 9 19 CSL3 23 16 17 18 OVP CSH3 15 14 11 12 10 22 VCC 13 MAX1537A 6 Chip Information 28 29 30 31 SKIP DH5 BST5 LX5 IN CSH5 33 32 INA SHDN 35 34 LDOA 36 TOP VIEW PGDLY PGOOD UVP DH3 BST3 LX3 MAX1533A/MAX1537A Pin Configurations (continued) LDO5 DL5 THIN QFN 6mm x 6mm 36 ______________________________________________________________________________________ High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers QFN THIN.EPS ______________________________________________________________________________________ 37 MAX1533A/MAX1537A Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.) Package Information (continued) (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.) QFN THIN.EPS MAX1533A/MAX1537A High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 38 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2006 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.