RT8203 High-Efficiency, Quad Output, Main Power-Supply Controllers for Notebook Computers General Description Features The RT8203 dual step-down, Switch Mode Power Supply (SMPS) controllers generate logic-supply voltages in battery-powered systems. The RT8203 include two pulsewidth modulation (PWM) controllers, adjustable from 2V to 5.5V or fixed at 5V and 3.3V. These devices feature two linear regulators providing 5V and 3.3V always-on outputs. Each linear regulator provides up to 100mA output current with automatic linear regulator bootstrapping to the main SMPS outputs. The RT8203 include on-board power-up sequencing, a power good (PGOOD) output, internal softstart, and soft-shutdown output discharge that prevents negative voltages on shutdown. Richtek's proprietary MachPWMTM “instant-on” response, constant on-time PWM control scheme operates without sense resistors and provides 100ns response to load transients while maintaining a relatively constant switching frequency. The unique ultrasonic mode maintains the switching frequency above 25kHz, which eliminates noise in audio applications. Other features include diode-emulation, which maximizes efficiency in light-load applications, and fixed-frequency PWM mode, which reduces RF interference in sensitive applications. The RT8203 provides a pin-selectable switching frequency, allowing either 200kHz/300kHz or 400kHz/500kHz operation of the 5V/3.3V SMPSs, respectively. The RT8203 is available in SSOP-28 package. z Ordering Information RT8203 Package Type A : SSOP-28 Lead Plating System P : Pb Free G : Green (Halogen Free and Pb Free) z z z z z z z z z z z z No Current Sense Resistor Needed 1.5% Output Voltage Accuracy 3.3V and 5V 100mA Bootstrapped Linear Regulators Internal Soft-Start and Soft-Shutdown Output Discharge Mach-PWM with 100ns Load Step Response 3.3V and 5V Fixed or Adjustable Outputs 7V to 24V Input Voltage Range Ultrasonic Mode Operation 25kHz (min.) Power Good (PGOOD) Signal Over Voltage Protection Under Voltage Protection Over Temperature Protection RoHS Compliant and 100% Lead (Pb)-Free Applications z z z Notebook and Subnotebook Computers PDAs and Mobile Communication Devices 3- and 4-Cell Li+ Battery-Powered Devices Pin Configurations (TOP VIEW) NC PGOOD ON3 ON5 ILIM3 EN FB3 VREF FB5 PRO ILIM5 SKIP TON BOOT5 28 27 2 26 3 25 4 24 5 23 6 22 7 21 8 20 9 19 10 18 11 17 12 16 13 SSOP-28 15 14 BOOT3 PHASE3 UGATE3 LDO3 LGATE3 GND VOUT3 VOUT5 VIN LGATE5 LDO5 VCC UGATE5 PHASE5 Note : Richtek products are : ` SSOP-28 RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. ` Suitable for use in SnPb or Pb-free soldering processes. DS8203-05 April 2011 www.richtek.com 1 RT8203 Typical Application Circuit 5V ALWAYS ON VIN 7V to 24V + C1 4.7µF 18 C2 1µF R2 47 R1 3.9 LDO5 17 3 ON3 4 ON5 VCC 5 VCC ILIM3 11 ILIM5 C3 1µF D1 C6 10µF C10 L1 VCC 25 3.3V ALWAYS ON R6 20 C5 0.1µF VOUT5 5V LDO3 VREF Q1 AO4702 VIN RT8203 PRO BAT254 R3 2.2 14 BOOT5 C8 0.1µF 16 UGATE5 15 EN C4 4.7µF 10 1M D2 BAT254 6 R4 2.2 BOOT3 28 OFF PHASE3 LGATE5 LGATE3 C7 10µF C9 0.1µF UGATE3 26 PHASE5 Q2 AO4702 19 Q3 VOUT3 3.3V L2 27 BSC119N03 D3 ON D4 24 C11 Q4 BSC119N03 SEE TABLE 13 TON 21 VOUT5 8 VREF C12 0.22µF 9 23 FB5 GND VOUT3 SKIP 22 12 VCC 7 FB3 1 NC PGOOD R5 100k 2 Power-Good INDICATOR Frequency-dependent Components VOUT5 VOUT3 TON = VCC TON = GND TON = VCC TON = GND f = 200kHz L1 = 7.6μH f = 400kHz L1 = 5.6μH f = 300kHz L2 = 4.7μH f = 500kHz L2 = 3μH C10 = 330μF C10 = 150μF C11 = 470μF C11 = 220μF Figure 1. Fixed Voltage Regulator www.richtek.com 2 DS8203-05 April 2011 RT8203 5V ALWAYS ON + VIN 7V to 24V 18 C1 4.7µF C2 1µF R2 47 R1 3.9 LDO5 17 3 ON3 4 ON5 VCC 5 VCC ILIM3 11 ILIM5 C3 1µF 3.3V ALWAYS ON C6 10µF Q1 AO4702 VIN RT8203 PRO R3 2.2 14 BOOT5 C8 0.1µF 16 UGATE5 15 EN C4 4.7µF 10 1M BAT254 D1 L1 VCC 25 R6 20 C5 0.1µF VOUT5 5V LDO3 VREF D2 BAT254 6 R4 2.2 BOOT3 28 OFF PHASE3 LGATE5 LGATE3 C7 10µF C9 0.1µF UGATE3 26 PHASE5 ON Q2 AO4702 BSC119N03 C10 D3 19 Q3 VOUT3 3.3V L2 27 D4 24 Q4 C11 BSC119N03 SEE TABLE C13 0.1µF R7 15k R8 10k 13 TON 21 VOUT5 9 FB3 FB5 8 VREF C12 0.22µF 23 VOUT3 22 GND R9 6.5k 7 12 SKIP 1 NC VCC R5 100k PGOOD 2 R10 10k C14 0.1µF Power-Good INDICATOR Frequency-dependent Components VOUT5 VOUT3 TON = VCC TON = GND TON = VCC TON = GND f = 200kHz L1 = 7.6μH f = 400kHz L1 = 5.6μH f = 300kHz L2 = 4.7μH f = 500kHz L2 = 3μH C10 = 330μF C10 = 150μF C11 = 470μF C11 = 220μF Figure 2. Adjustable Voltage Regulator DS8203-05 April 2011 www.richtek.com 3 RT8203 Functional Pin Description Pin No. Pin Name 1 NC 2 PGOOD Pin Function Connect to GND. Power Good Open Drain Output. PGOOD is pulled low if either output is disable or is more than 8.75% below its normal value. VOUT3 Enable Input. The 3.3V SMPS is enable if ON3 is greater than the on level 3 ON3 and disable if ON3 is less than the off level. If ON3 is connected to VREF, the 3.3V SMPS starts after the 5V SMPS reached regulation(delay start). Force ON3 below the clear fault level to reset the fault latched. VOUT5 Enable Input. The 5V SMPS is enable if ON5 is greater than the on level and 4 ON5 disable if ON5 is less than the off level. If ON5 is connected to VREF, the 5V SMPS starts after the 3.3V SMPS reached regulation(delay start). Force ON5 below the clear fault level to reset the fault latched. VOUT3 Current Limit Adjustment. The GND-PHASE3 current limit threshold defaults 5 ILIM3 to 100mV if ILIM3 is tied to VCC. In adjustable mode, the current limit threshold is 1/10 the voltage seen at ILIM3 over 0.5V to 3V range. The logic threshold for switch over to 100mV default value is approximately VCC − 1V. Enable Control Input. The device enters its 15μA supply current shutdown mode if EN is less than the EN input falling edge trip level and does not restart until EN is greater 6 EN than the EN input rising edge trip level. Connect EN to VIN for automatically startup. EN can be connected to VIN through a resistive voltage divider to implement a programmable undervoltage lockout. 7 FB3 VOUT3 Feedback Input. Connect FB3 to GND for fixed 3.3V operation. Connect FB3 to a resistive voltage divider from VOUT3 to GND to adjust the output from 2V to 5.5V. 2V Reference Output. Bypass to GND with a 0.22μF(MIN) capacitor. VREF can source 8 VREF up to 100μA for external loads. Loading VREF degrades FBx and VOUTx accuracy according to the VREF load regulation error. 9 10 FB5 PRO VOUT5 Feedback Input. Connect FB5 to GND for fixed 5V operation. Connect FB5 to a resistive voltage divider from VOUT5 to GND to adjust the output from 2V to 5.5V. Over Voltage and Under Voltage Fault Protection Enable/Disable. Connect PRO to VCC to disable Over Voltage and Under Voltage protection. Connect PRO to GND to enable Over Voltage and Under Voltage protection. VOUT5 Current Limit Adjustment. The GND − PHASE5 current limit threshold defaults 11 ILIM5 to 100mV if ILIM5 is tied to VCC. In adjustable mode, the current limit threshold is 1/10 the voltage seen at ILIM5 over 0.5V to 3V range. The logic threshold for switch over to 100mV default value is approximately VCC − 1V. 12 SKIP Operation Mode Input Control. Connect SKIP to GND for diode-emulation mode (DEM) or to VCC for CCM mode(fixed frequency). Connect to VREF or floating for ultrasonic mode. 13 TON 14 BOOT5 Frequency Select Input. Connect to VCC for 200kHz/300kHz operation and to GND for 400kHz/500kHz operation (VOUT5/VOUT3 switching frequency respectively). Boost Capacitor Connection for 5V SMPS. Connect an external ceramic capacitor to PHASE5 and an external diode to LDO5. To be continued www.richtek.com 4 DS8203-05 April 2011 RT8203 Pin No. Pin Name 15 PHASE5 16 UGATE5 17 VCC 18 LDO5 19 LGATE5 20 VIN 21 VOUT5 22 VOUT3 23 GND 24 LGATE3 25 LDO3 Pin Function Inductor Connection for 5V SMPS. PHASE5 is the internal lower supply rail for the UGATE5 high side gate driver, and the current sense input for the 5V SMPS. High Side N-MOSFET Floating Gate-Driver Output for VOUT5. Swings between PHASE5 and BOOT5. Analog Supply Voltage Input for the internal analog integrated circuit. Bypass to GND with a 1μF ceramic capacitor. 5V Linear Regulator Output. LDO5 is the gate driver supply for the external MOSFETs. LDO5 can provide a total of 100mA, including the MOSFET gate-driver requirements and external loads. If VOUT5 is greater than the LDO5 switchover threshold, the LDO5 regulator shuts down and LDO5 pin connects to VOUT5 through a 1.4Ω switch. Bypass a 4.7μF ceramic capacitor to GND. Low side N-MOSFET Gate-Drive Output for VOUT5. Swings between GND and LDO5. Power-Supply Input. VIN powers the LDO5/LDO3 linear regulators and is also used for PWM control circuits. Connect VIN to the battery input or the AC adapter output. VOUT5 Sense Input. Connect to the 5V output. VOUT5 is an input to the PWM control circuit. It also serves as the 5V feedback input in fixed-voltage mode. If VOUT5 is greater than the LDO5 switchover threshold, the LDO5 shuts down and LDO5 connects to VOUT5 through 1.4Ω switch. VOUT3 Sense Input. Connect to the 3.3V output. VOUT3 is an input to the PWM control circuit. It also serves as the 3.3V feedback input in fixed voltage mode. If VOUT3 is greater than the LDO3 switchover threshold, the LDO3 shuts down and LDO3 connects to VOUT3 through 1.5Ω switch. Analog and Power Ground. Low side N-MOSFET Gate-Drive Output for VOUT3. Swings between GND and LDO5. 3.3V Linear Regulator Output. LDO3 can provide a total of 100mA to external loads. If VOUT3 is greater than the LDO3 switchover threshold, the LDO3 regulator shuts down and LDO3 pin connects to VOUT3 through a 1.5Ω switch. Bypass a 4.7μF ceramic capacitor to GND. High Side N-MOSFET Floating Gate-Driver Output for VOUT3. Swings between PHASE3 and BOOT3. 26 UGATE3 27 PHASE3 Inductor Connection for 3.3V SMPS. PHASE3 is the internal lower supply rail for the UGATE3 high side gate driver, and the current sense input for the 3.3V SMPS. 28 BOOT3 Boost Capacitor Connection for 3.3V SMPS. Connect an external ceramic capacitor to PHASE3 and an external diode to LDO5. DS8203-05 April 2011 www.richtek.com 5 RT8203 Function Block Diagram VIN PGOOD GND BOOT3 UGATE3 PHASE3 Driver LGATE3 Driver U3 Driver BOOT5 UGATE5 PHASE5 Driver LGATE5 U5 VOUT5 PWM Controller VOUT3 PWM Controller L3 L5 ILIM3 FB3 VOUT3 ILIM5 FB5 VOUT5 + + 4.65V - EN5 2.93V - EN3 LDO (5V) LDO5 LDO (3V) LDO3 ON3 ON5 EN PRO LDO5 VCC Power Sequence Logic Thermal Shutdown 2V Reference VREF VIN Ton 1-SHOT R VOUTx QN Ton On-time Compute Ux TRIG QN TRIG Min. Toff 1-SHOT VREF - + GM - + Comp 25Khz Detector SS (internal) Lx FBx + 1.1xVREF OV - PRO + UV S1 S2 Latch Q 0.7xVREF Zero Detector + Current Limit + + 0.9xVREF SKIP - PHASEx + ILIMx - PGOOD PWM Controller www.richtek.com 6 DS8203-05 April 2011 RT8203 Absolute Maximum Ratings z z z z z z z z z z z z z z z z z z (Note 1) Input Voltage, VIN, EN to GND -----------------------------------------------------------------------------BOOTx to GND ------------------------------------------------------------------------------------------------PHASEx to BOOTx -------------------------------------------------------------------------------------------PHASEx to GND -----------------------------------------------------------------------------------------------VCC, LDOx, VOUTx, ONx, VREF, FBx, SKIP, PRO, PGOOD to GND --------------------------UGATEx to PHASEx -----------------------------------------------------------------------------------------ILIMx to GND ---------------------------------------------------------------------------------------------------LGATEx to GND -----------------------------------------------------------------------------------------------TON to GND -----------------------------------------------------------------------------------------------------LDOx, VREF Short Circuit to GND ------------------------------------------------------------------------LDOx Circuit (Internal Regulator) Continuous ----------------------------------------------------------LDOx Circuit (Switchover to VOUTx) Continuous -----------------------------------------------------Power Dissipation, PD @ TA = 25°C SSOP-28 -------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) SSOP-28, θJA ---------------------------------------------------------------------------------------------------Junction Temperature -----------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------Storage Temperature Range --------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Mode) ----------------------------------------------------------------------------------MM (Machine Mode) ------------------------------------------------------------------------------------------- Recommended Operating Conditions z z z z −0.3V to 25V −0.3V to 30V −6V to 0.3V −1V to 25V −0.3V to 6V −0.3V to (VBOOTx + 0.3V) −0.3V to (VCC + 0.3V) −0.3V to (VLDO5 + 0.3V) −0.3V to 6V Momentary 100mA 200mA 1.053W 95°C/W 150°C 260°C –65°C to 150°C 2kV 200V (Note 4) Input Voltage, VIN ----------------------------------------------------------------------------------------------Control Voltage, VCC ------------------------------------------------------------------------------------------Junction Temperature Range --------------------------------------------------------------------------------Ambient Temperature Range --------------------------------------------------------------------------------- 7V to 24V 5V ± 5% –10°C to 125°C –10°C to 85°C Electrical Characteristics (VIN = 12V, No load on LDOx, VOUTx and VREF, ONx = VCC, VEN = 5V, TA = 25°C, unless Otherwise specification) Parameter Symbol Test Conditions Min Typ Max Unit 7 -- 24 V 3.285 3.330 3.375 V VIN = 8V to 24V, FB5 = GND, VSKIP = 5V 4.975 5.059 5.125 V Output Voltage in Adjustable Mode VIN = 7V to 24V, either SMPS 1.975 2.00 2.025 V Output Voltage Adjust Range FBx Adjustable-Mode Threshold Voltage Either SMPS 2 -- 5.5 V 0.12 -- 0.22 V Main SMPS Controllers Input Voltage Range VOUT3 Output Voltage in Fixed Mode VOUT5 Output Voltage in Fixed Mode VIN VOUT3 VOUT5 LDO5 in regulation VIN = 7V to 24V, FB3 = GND, VSKIP = 5V Dual-Mode comparator To be continued DS8203-05 April 2011 www.richtek.com 7 RT8203 Parameter Symbol Test Conditions Min Typ Max -- −0.1 -- -- −1.5 -- Either SMPS, VSKIP = 2V, 0 to 5A -- −1.7 -- Either SMPS, 7V< VIN <24V --- 0.005 -- %/V ILIMx = VCC , GND to PHASEx 90 100 110 mV VILIMx = 0.5V, GND to PHASEx 40 50 60 VILIMx = 1V, GND to PHASEx 90 100 110 VILIMx = 2V, GND to PHASEx SKIP = GND, I LIMx = VCC, GND − PHASEx 185 200 215 --- 3 1.5 ---- VTON = 5V, 5V SMPS VSKIP = VCC 3.3V SMPS -- 200 -- -- 300 -- VTON = GND 5V SMPS VSKIP = VCC 3.3V SMPS -- 400 -- -- 500 -- 25 -- -- VOUT5 = 5.05V 1.854 2.060 2.265 VOUT3 = 3.33V 0.821 0.912 1.003 VOUT5 = 5.05V 0.876 1.030 1.184 VOUT3 = 3.33V 0.467 0.546 0.625 300 400 500 VOUT5 = 5.05V -- 92 -- VOUT3 = 3.33V -- 88 -- VOUT5 = 5.05V -- 84 -- VOUT3 = 3.33V -- 80 -- 4.90 5.0 5.10 V -- 350 -- mA 3.95 4.25 4.55 V 4.52 4.65 4.78 V LDO5 to VOUT5, VOUT5 = 5V -- 1.4 3.2 Ω LDO3 Output Voltage ONx = GND, 7V < VIN < 24V, 0 < I LDO3 < 100mA (Note 5) 3.28 3.35 3.42 V LDO3 Short-Circuit Current LDO3 Bootstrap Switch Threshold LDO3 = GND Falling edge of VOUT3, rising edge at VOUT3 regulation point -- 175 -- mA 2.82 2.93 3.04 V Either SMPS, VSKIP = 5V, 0 to 5A DC Load Regulation Line Regulation Current-Limit Threshold (Positive, Default) ΔVLOAD Either SMPS, VSKIP = GND, 0 to 5A ΔVLINE Current-Limit Threshold (Positive, Adjustable) Zero-Current Threshold Soft-Start Ramp Time Operating Frequency Zero to full limit f OSC SKIP = VREF VTON = 5V On-Time Pulse Width VTON = GND Minimum Off-time t OFF VTON = 5V Maximum Duty Cycle VTON = GND Internal Regulator And Reference Voltage ONx = GND, 7V < VIN < 24V, LDO5 Output Voltage 0 < I LDO5 < 100mA (Note 5) LDO5 Short-Circuit Current VCC Under-Voltage Lockout Fault Threshold LDO5 Bootstrap Switch Threshold LDO5 Bootstrap Switch Resistance LDO5 = GND Falling edge of VCC, hysteresis = 1% Falling edge of VOUT5, rising edge at VOUT5 regulation point Unit % mV mV ms kHz μs ns % To be continued www.richtek.com 8 DS8203-05 April 2011 RT8203 Parameter Min Typ Max Unit -- 1.5 3.5 Ω No external load 1.98 2 2.02 V VREF Load Regulation 0 < I LOAD < 50μA -- -- 10 mV VREF Sink Current VREF in regulation 10 -- -- μA VIN Standby Supply Current VIN Shutdown Supply Current I Standby VIN = 7V to 24V, both SMPSs off, includes IEN -- 150 250 μA I SD VIN = 7V to 24V -- 15 25 μA Both SMPSs on, FBx = SKIP = GND, VOUT3 = 3.5V, VOUT5 = 5.3V (Note 6) -- 3.5 5 mW FBx with respect to nominal regulation point 8 11 14 % FBx delay with 50mV overdrive -- 20 -- μs −11.25 −8.75 −6.25 % -- 5 -- μs ISINK = 4mA -- -- 0.3 V High state, forced to 5.5V -- -- 1 μA -- 150 -- °C FBx with respect to nominal output voltage 65 70 75 % From ONx signal going high 10 22 35 ms −200 40 200 nA Low level -- -- 0.6 High level 1.5 -- -- Low level -- -- 0.8 Float level 1 -- 2.3 High level 2.4 -- -- Low level -- -- 0.8 High level 2.4 -- -- -- -- 0.8 Delay start level 1.3 -- 2.3 SMPS on level 2.4 -- -- VPRO or VTON = 0 or 5V VONx = 0 or 5V −1 -- 2 −2 -- 2 LDO3 Bootstrap Switch Resistance VREF Output Voltage Symbol Test Conditions LDO3 to VOUT3, VOUT3 = 3.2V VREF Quiescent Power Consumption Fault Detection Over Voltage Trip Threshold Over Voltage Fault Propagation Delay FBx with respect to nominal output, falling edge, typical hysteresis = 1% Falling edge, 50mV overdrive PGOOD Threshold PGOOD Propagation Delay PGOOD Output Low Voltage PGOOD Leakage Current Thermal Shutdown Threshold Output Undervoltage Shutdown Threshold Output Undervoltage Shutdown Blanking Time Inputs and Outputs Feedback Input Leakage Current PRO Input Threshold Voltage SKIP Input Threshold Voltage TON Input Threshold Voltage TSD ΔTSD VFBx = 2.2V Clear fault level/SMPS off level ON3, ON5 Input Threshold Voltage Input Leakage Current V V V V μA To be continued DS8203-05 April 2011 www.richtek.com 9 RT8203 Parameter Input Leakage Current EN Input Trip level UGATEx Driver Sink/Source Current LGATEx Driver Source Current LGATEx Driver Sink Current UGATEx Driver On-Resistance LGATEx Driver On-Resistance Symbol Conditions Min Typ Max V SKIP = 0 or 5V V EN = 0 or 24V −1 -- 5 −1 -- 3 V ILIMx = 0 or 2V −0.2 -- 0.2 Rising edge 1.2 1.6 2 Falling edge 0.96 1 1.04 UGATEx forced to 2V -- 2 -- A LGATEx (source) forced to 2V -- 1.7 -- A LGATEx (sink) forced to 2V -- 3.3 -- A (BOOTx to PHASEx) forced to 5V -- 1.5 4 Ω LGATEx, High State (pull up) -- 2.2 5.0 LGATEx, Low State (pull down) -- 0.6 1.5 -- 17.7 40 VOUTx Discharge-Mode On-Resistance Unit μA V Ω Ω Note 1. Stresses listed as the above “Absolute Maximum Ratings” may cause permanent damage to the device. These are for stress ratings. 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 remain possibility to affect device reliability. Note 2. θJA is measured in the natural convection at TA = 25°C on a low effective single layer thermal conductivity test board of JEDEC 51-3 thermal measurement standard. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Note 5. ILDO3 + ILDO5 < 150mA Note 6. PVIN + PVCC www.richtek.com 10 DS8203-05 April 2011 RT8203 Typical Operating Characteristics No load on LDO5, LDO3,VOUT5, VOUT3 and REF, TON = VCC, EN = VIN, TA = 25°°C, unless otherwise specified. VOUT5 Efficiency vs. Load Current 100 90 90 80 80 70 Diode-Emulation Mode Ultrasonic Mode 60 Efficiency (%) Efficiency (%) VOUT5 Efficiency vs. Load Current 100 Forced CCM Mode 50 40 30 20 0 0.001 0.01 0.1 1 Diode-Emulation Mode 60 Ultrasonic Mode 50 Forced CCM Mode 40 30 20 VIN = 8V ON3 = GND, ON5 = VCC COUT = 330μF, L = 7.6μH 10 70 VIN = 12V, ON3 = GND, ON5 = VCC COUT = 330μF, L = 7.6μH 10 0 0.001 10 0.01 90 90 80 80 70 70 Diode-Emulation Mode Ultrasonic Mode 40 Forced CCM Mode 30 VIN = 24V, ON3 = GND, ON5 = VCC COUT = 330μF, L = 7.6μH 20 10 0 0.001 0.01 0.1 1 Diode-Emulation Mode 60 Ultrasonic Mode 50 40 Forced CCM Mode 30 20 VIN = 8V, ON3 = ON5 = VCC COUT = 470μF, L = 4.7μH 10 0 0.001 10 0.01 90 90 80 80 70 70 Diode-Emulation Mode 50 Ultrasonic Mode Forced CCM Mode 20 VIN = 12V, ON3 = ON5 = VCC COUT = 470μF, L = 4.7μH 10 0 0.001 0.01 0.1 Load Current (A) DS8203-05 April 2011 1 10 Efficiency (%) Efficiency (%) 100 30 1 10 VOUT3 Efficiency vs. Load Current VOUT3 Efficiency vs. Load Current 100 40 0.1 Load Current (A) Load Current (A) 60 10 VOUT3 Efficiency vs. Load Current 100 Efficiency (%) Efficiency (%) VOUT5 Efficiency vs. Load Current 100 50 1 Load Current (A) Load Current (A) 60 0.1 Diode-Emulation Mode 60 Ultrasonic Mode 50 40 Forced CCM Mode 30 20 VIN = 24V, ON3 = ON5 = VCC COUT = 470μF, L = 4.7μH 10 0 0.001 0.01 0.1 1 10 Load Current (A) www.richtek.com 11 VOUT5 Switching Frequency vs. Load Current VOUT5 Switching Frequency vs. Load Current 250 250 225 Forced CCM Mode 200 175 150 125 VIN = 8V, ON3 = GND, ON5 = VCC, COUT = 330μF, L = 7.6μH 100 75 50 Ultrasonic Mode 25 Switching Frequency (kHz) Switching Frequency (kHz) RT8203 225 Forced CCM Mode 200 175 150 125 75 50 Ultrasonic Mode 25 Diode-Emulation Mode Diode-Emulation Mode 0 0.001 0.01 0.1 1 0 0.001 10 0.01 Forced CCM Mode 175 150 125 100 VIN = 24V, ON3 = GND, ON5 = VCC, COUT = 330μF, L = 7.6μH 75 Ultrasonic Mode 25 Switching Frequency (kHz) Switching Frequency (kHz) 225 0 0.001 0.1 1 Forced CCM Mode 280 240 200 160 80 40 Ultrasonic Mode 0 0.001 10 0.01 320 Forced CCM Mode 320 280 240 200 VIN = 12V, ON3 = VCC, ON5 = GND, COUT = 470μF, L = 4.7μH Ultrasonic Mode 0 0.001 0.1 Load Current (A) www.richtek.com 12 10 1 Forced CCM Mode 280 240 200 160 VIN = 24V, ON3 = VCC, ON5 = GND, COUT = 470μF, L = 4.7μH 120 80 40 Ultrasonic Mode Diode-Emulation Mode Diode-Emulation Mode 0.01 Switching Frequency (kHz) 360 80 1 VOUT3 Switching Frequency vs. Load Current 360 120 0.1 Load Current (A) VOUT3 Switching Frequency vs. Load Current 160 VIN = 8V, ON3 = VCC, ON5 = GND, COUT = 470μF, L = 4.7μH 120 Diode-Emulation Mode Diode-Emulation Mode 0.01 320 Load Current (A) Switching Frequency (kHz) 10 360 250 40 1 VOUT3 Switching Frequency vs. Load Current VOUT5 Switching Frequency vs. Load Current 50 0.1 Load Current (A) Load Current (A) 200 VIN = 12V, ON3 = GND, ON5 = VCC, COUT = 330μF, L = 7.6μH 100 10 0 0.001 0.01 0.1 1 10 Load Current (A) DS8203-05 April 2011 RT8203 LDO5 Output Voltage vs. Output Current LDO3 Output Voltage vs. Output Current 3.50 5.10 3.45 Output Voltage (V) Output Voltage (V) 5.05 5.00 4.95 3.40 3.35 3.30 4.90 3.25 VIN = 12V, ON3 = ON5 = GND VIN = 12V, ON3 = ON5 = GND 3.20 4.85 0 10 20 30 40 50 60 70 80 90 0 100 10 20 VREF vs. Output Current 50 60 70 80 90 100 No Load VIN Current vs. Input Voltage 2.005 100 Forced CCM Mode No Load V IN Current (mA) 2.003 2.001 V REF (V) 40 Output Current (mA) Output Current (mA) 1.999 1.997 1.995 1.993 1.991 VIN = 12V, ON3 = ON5 = GND 10 Ultrasonic Mode 1 Diode-Emulation Mode VIN = 12V, ON3 = ON5 = VCC 1.989 0.1 -10 0 10 20 30 40 50 60 70 80 90 100 7 9 11 Output Current (uA) 13 15 17 19 21 23 25 Input Voltage (V) VIN Standby Input Current vs. Input Voltage VIN Shutdown Input Current vs. Input Voltage 230 20 228 226 224 222 220 218 216 214 VIN = 12V, ON3 = ON5 = GND 212 210 V IN Shutdown Input Current (uA) V IN Standby Input Current (uA) 30 19 18 17 16 15 14 13 12 VIN = 12V, ON3 = ON5 = GND, EN = GND 11 10 7 9 11 13 15 17 19 Input Voltage (V) DS8203-05 April 2011 21 23 25 7 9 11 13 15 17 19 21 23 25 Input Voltage (V) www.richtek.com 13 RT8203 Power Up VIN (10V/Div) Delayed Start ON5 (5V/Div) LDO5 (2V/Div) VOUT5 (2V/Div) LDO3 (2V/Div) REF (2V/Div) VIN = 12V, ON3 = ON5 = GND VOUT3 (2V/Div) VIN = 12V, ON3 = REF Time (400μs/Div) Time (400μs/Div) Delayed Start Shutdown Response ON5 (10V/Div) SKIP = VCC(Forced CCM Mode) ON3 (5V/Div) VOUT5 (5V/Div) VOUT5 (2V/Div) UGATE5 (20V/Div) VOUT3 (2V/Div) VIN = 12V, ON5 = REF LGATE5 (5V/Div) VIN = 12V, ON3 = ON5 = VCC Time (400μs/Div) Time (10ms/Div) VOUT5 Load Transient Response VOUT3 Load Transient Response VIN = 12V, SKIP = VCC(Forced CCM Mode) VIN = 12V, SKIP = VCC(Forced CCM Mode) VOUT_ac-coupled (100mV/Div) VOUT_ac-coupled (100mV/Div) Inductor Current (5A/Div) Inductor Current (5A/Div) LGATE5 (5V/Div) LGATE3 (5V/Div) ON3 = ON5 = VCC, COUT = 330μF, L = 7.6μH Time (20μs/Div) www.richtek.com 14 ON3 = ON5 = VCC, COUT = 470μF, L = 4.7μH Time (10μs/Div) DS8203-05 April 2011 RT8203 VOUT5 OVP VOUT5 UVP SKIP = GND(Diode-Emulation Mode) SKIP = VCC(Forced CCM Mode) VOUT5 (5V/Div) VOUT5 (5V/Div) LGATE5 (5V/Div) Inductor Current (10A/Div) UGATE5 (20V/Div) VOUT3 (2V/Div) LGATE5 (5V/Div) LGATE3 (10V/Div) VIN = 12V, ON3 = ON5 = VCC Time (2ms/Div) VIN = 12V, ON3 = ON5 = VCC Time (10μs/Div) VOUT5 Shorted Start Up VOUT5 (2V/Div) VOUT5 Shorted, SKIP = VCC(Forced CCM Mode) Inductor Current (5A/Div) UGATE5 (20V/Div) LGATE5 (5V/Div) VIN = 12V, COUT = 330μF, L = 7.6μH Time (2ms/Div) DS8203-05 April 2011 www.richtek.com 15 RT8203 Application Information The RT8203 is a dual, Mach ResponseTM DRVTM dual ramp valley mode synchronous buck controller. The controller is designed for low voltage power supplies for notebook computers. Richtek's Mach ResponseTM technology is specifically designed for providing 100ns “instant-on” response to load steps while maintaining a relatively constant operating frequency and inductor operating point over a wide range of input voltages. The topology circumvents the poor load transient timing problems of fixed-frequency current mode PWMs while avoiding the problems caused by widely varying switching frequencies in conventional constant-on-time and constant off-time PWM schemes. The DRVTM mode PWM modulator is specifically designed to have better noise immunity for such a dual output application. The RT8203 includes 5V (LDO5) and 3.3V (LDO3) linear regulators. LDO5 linear regulator can step down the battery voltage to supply both internal circuitry and gate drivers. The synchronous-switch gate drivers are directly powered from LDO5. When VOUT5 voltage is above 4.65V, an automatic circuit turns off the LDO5 linear regulator and powers the device form VOUT5. PWM Operation The Mach ResponseTM DRVTM mode controller relies on the output filter capacitor's effective series resistance (ESR) to act as a current sense resistor, so the output ripple voltage provides the PWM ramp signal. Refer to the RT8203's function block diagram, the synchronous high side MOSFET is turned on at the beginning of each cycle. After the internal one-shot timer expires, the MOSFET is turned off. The pulse width of this one shot is determined by the converter's input voltage and the output voltage to keep the frequency fairly constant over the input voltage range. Another one shot sets a minimum off-time (400ns typ). The on-time one shot is triggered if the error comparator is high, the low side switch current is below the current limit threshold, and the minimum off-time one shot has timed out. high side switch on-time is inversely proportional to the input voltage as measured by the VIN, and proportional to the output voltage. There are two benefits of a constant switching frequency. The first is the frequency can be selected to avoid noise sensitive regions such as the 455kHz IF band. The second is the inductor ripple-current operating point remains relatively constant, resulting in easy design methodology and predictable output voltage ripple. The frequency for 5V SMPS is set at 100kHz higher than the frequency for 3V SMPS. This is done to prevent audiofrequency “beating” between the two sides, which switch asynchronously for each side. The on-time is given by : On-Time = K ( VOUT / VIN) where K is set by the TON pin-strap connection (Table 1). The on-times guaranteed in the Electrical Characteristics tables are influenced by switching delays in the external high-side power MOSFET. Two external factors that influence switching frequency accuracy are resistive drops in the two conduction loops (including inductor and PC board resistance) and the dead-time effect. These effects are the largest contributors to the change of frequency with changing load current. The dead time effect increases the effective on-time, reducing the switching frequency as one or both dead times. It occurs only in Forced CCM Mode (SKIP = high) when the inductor current reverses at light or negative load currents. With reversed inductor current, the inductor’ s EMF causes PHASEx to go high earlier than normal, extending the on-time by a period equal to the low-to-high dead time. For loads above the critical conduction point, the actual switching frequency is : f= (VOUT + VDROP1) tON x (VIN + VDROP2) where VDROP1 is the sum of the parasitic voltage drops in the inductor discharge path, including synchronous rectifier, inductor, and PC board resistances; VDROP2 is the sum of the resistances in the charging path; and tON is the ontime calculated by the RT8203. PWM Frequency and On-Time Control Operation Mode Selection (SKIP) The Mach ResponseTM control architecture runs with pseudo-constant frequency by feed forwarding the input and output voltage into the on-time one shot timer. The The RT8203 supports three operation modes: DiodeEmulation Mode, Ultrasonic Mode, and Forced-CCM Mode. www.richtek.com 16 DS8203-05 April 2011 RT8203 Diode-Emulation Mode ( SKIP = GND) In Diode-Emulation mode, RT8203 automatically reduces switching frequency at light load conditions to maintain high efficiency. This reduction of frequency is achieved smoothly and without increase of VOUT ripple or load regulation. As the output current decreases from heavy load condition, the inductor current is also reduced, and eventually comes to the point that its valley touches zero current, which is the boundary between continuous conduction and discontinuous conduction modes. By emulating the behavior of diodes, the low side MOSFET allows only partial of negative current when the inductor free-wheeling current reach negative. As the load current further decreases, it takes longer and longer to discharge the output capacitor to the level that requires the next “ON ” cycle. The on-time is kept the same as that in the heavy load condition. In reverse, when the output current increases from light load to heavy load, the switching frequency increases to the preset value as the inductor current reaches the continuous conduction. The transition load point to the light load operation can be calculated as follows (Figure 3) : IL Slope = (V IN -V OUT) / L iL, peak iLoad = iL, peak / 2 0 tON t Figure 3. Boundary Condition of CCM/DCM ILOAD(SKIP) ≈ (VIN - VOUT ) × t ON 2L where Ton is the On-time. The switching waveforms may appear noisy and asynchronous when light loading causes Diode-Emulation 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 DS8203-05 April 2011 using higher inductor values include larger physical size and degraded load transient response (especially at low input-voltage levels). Ultrasonic Mode ( SKIP = Float) Leaving SKIP unconnected or connecting SKIP to VREF activates a unique Diode-Emulation mode with a minimum switching frequency of 25kHz. This ultrasonic mode eliminates audio-frequency modulation that would otherwise be present when a lightly loaded controller automatically skips pulses. In ultrasonic mode, the lowside switch gate-driver signal is OR with an internal oscillator (>25kHz). Once the internal oscillator is triggered, the ultrasonic controller pulls LGATEx high, turning on the low side MOSFET to induce a negative inductor current. After the output voltage across the VREF, the controller turns off the low side MOSFET (LGATEx pulled low) and triggers a constant on-time (UGATEx driven high). When the ontime has expired, the controller re-enables the low-side MOSFET until the controller detects that the inductor current drops below the zero-crossing threshold. Forced-CCM Mode ( SKIP = VCC) The low noise, forced-CCM mode ( SKIP = VCC) disables the zero-crossing comparator, which controls the low-side switch on-time. This causes the low side gate-driver waveform to become the complement of the high side gatedriver waveform. This in turn causes the inductor current to reverse at light loads as the PWM loop strives to maintain a duty ratio of VOUT/VIN. The benefit of forced-CCM mode is to keep the switching frequency fairly constant, but it comes at a cost: The no-load battery current can be 10mA to 40mA, depending on the external MOSFETs. Reference and linear Regulators (VREF, LDOx) The 2V reference (VREF) is accurate within ± 1% over temperature, making VREF useful as a precision system reference. Bypass VREF to GND with 0.22μF(min) capacitor. VREF can supply up to 100uA for external loads. Loading VREF reduces the VOUTx output voltage slightly because of the reference load-regulation error. LDO5 regulator supplies total of 100mA for internal and external loads, including MOSFET gate driver and PWM controller. LDO3 regulator supplies up to 100mA for external loads. Bypass LDO5 and LDO3 with a minimum 4.7uF www.richtek.com 17 RT8203 load; use an additional 1μF per 5mA of internal and external load. When the 5V main output voltage is above the LDO5 switchover threshold, an internal 1.4Ω N-MOSFET switch connects VOUT5 to LDO5 while simultaneously shutting down the LDO5 linear regulator. Similarly, when the 3.3V main output voltage is above the LDO3 switchover threshold, an internal 1.5Ω N-MOSFET switch connects VOUT3 to LDO3 while simultaneously shutting down the LDO3 linear regulator. It can decrease the power dissipation from the same battery, because the converted efficiency of SMPS is better than the converted efficiency of linear regulator. Current Limit Setting (ILIMx) The RT8203 has cycle-by-cycle current limiting control. The current limit circuit employs a unique “valley” current sensing algorithm. If the magnitude of the current sense signal at PHASEx is above the current limit threshold, the PWM is not allowed to initiate a new cycle (Figure 4). The actual peak current is greater than the current limit threshold by an amount equal to the inductor ripple current. Therefore, the exact current limit characteristic and maximum load capability are a function of the sense resistance, inductor value, and battery and output voltage. IL IL, peak ILoad ILIM 0 t when ILIMx is connected to VCC. The logic threshold for switchover to the 100mV default value is approximately VCC - 1V. Carefully observe the PC board layout guidelines to ensure that noise and DC errors do not corrupt the current-sense signal at PHASEx and GND. Mount or place the IC close to the low side MOSFET. MOSFET Gate Driver (UGATEx, LGATEx) The high side driver is designed to drive high current, low RDS(on) NMOSFET(s). When configured as a floating driver, 5-V bias voltage is delivered from LDO5 supply. The average drive current is also calculated by the gate charge at VGS = 5 V times switching frequency. The instantaneous drive current is supplied by the flying capacitor between BOOTx and PHASEx pins. A dead time to prevent shoot through is internally generated between high side MOSFET off to low side MOSFET on, and low side MOSFET off to high side MOSFET on. The low side driver is designed to drive high current low RDS(on) NMOSFET(s). The internal pull-down transistor that drives LGATEx low is robust, with a 0.6Ω typical onresistance. A 5V bias voltage is delivered from LDO5 supply. For high current applications, some combinations of high and low side MOSFETs may cause excessive gate-drain coupling, which can lead to efficiency-killing and EMIproducing shoot-through currents. This is often remedied by adding a resistor in series with BOOTx, which increases the turn-on time of the high side MOSFET without degrading the turn-off time (Figure 5). Figure 4. “Valley” Current Limit +5V The RT8203 uses the on-resistance of the synchronous rectifier as the current sense element. Use the worse-case maximum value for RDS(ON) from the MOSFET data sheet, and add a margin of 0.5%/°C for the rise in RDS(ON) with temperature. The current limit threshold is adjusted with an external voltage divider at ILIMx. The current limit threshold adjustment range is from 50 mV to 200mV. In the adjustable mode, the current limit threshold voltage is precisely 1/10 the voltage seen at ILIMx. The threshold defaults to 100mV www.richtek.com 18 BOOTx V IN 10R UGATEx PHASEx Figure 5. Reducing the UGATEx Rise Time DS8203-05 April 2011 RT8203 Soft-Start Output Under Voltage Protection (UVP) A build-in soft-start is used to prevent surge current from power supply input after ONx is enabled. It clamps the ramping of internal reference voltage which is compared with the FBx signal. The typical soft-start duration is 1.5ms period. Furthermore, the maximum allowed current limit is segmented in 3 steps : 20%, 50%, and 100% during the 1.5ms period. The current limit steps can minimize the VOUT folded-back in the soft-start duration when RT8203 is determining fixed or adjustable output. The output voltage can be continuously monitored for under voltage. When under voltage protection is enabled ( PRO = GND), if the output is less than 70% of the error-amplifier trip voltage, under voltage protection is triggered, then both UGATEx and LGATEx gate drivers are forced low. In order to remove the residual charge on the output capacitor during the UV period, if PHASEx is greater than 1V, the LGATEx gate driver is forced high until PHASEx lower than 1V. Connect UVP to GND to disable under voltage protection. POR and UVLO Thermal Protection Power On Reset (POR) occurs when VIN rises above approximately 3.5V, resetting the fault latch and preparing the PWM for operation. Below 4.25V(min), the VCC undervoltage lockout (UVLO) circuitry inhibits switching by keeping UGATEx and LGATEx low. The RT8203 have thermal shutdown to prevent the overheat damage. Thermal shutdown occurs when the die temperature exceeds 150°C. All internal circuitry shuts down during thermal shutdown. The RT8203 will trigger thermal shutdown if LDOx is not supplied from VOUTx, while input voltage on VIN and drawing current form LDOx are too high. Even if LDOx is supplied from VOUTx, overloading the LDOx causes large power dissipation on automatic switches, which may result in thermal shutdown. Power Good Output (PGOOD) The PGOOD is an open-drain type output. PGOOD is actively held low in soft-start, standby, and shutdown. It is released when both outputs voltage above than 91.25% of nominal regulation point. The PGOOD goes low if either output turns of or is 8.75% below its nominal regulation point. Output Over Voltage Protection (OVP) The output voltage can be continuously monitored for over voltage. When over voltage protection is enabled, if the output exceeds the over voltage threshold, over voltage fault protection is triggered and the LGATEx low side gate drivers are forced high. This activates the low side MOSFET switch, which rapidly discharges the output capacitor and reduces the input voltage. Note that LGATEx latching high causes the output voltage to dip slightly negative when energy has been previously stored in the LC tank circuit. For loads that cannot tolerate a negative voltage, place a power Schottky diode across the output to act as a reverse polarity clamp. Connect PRO to GND to enable the default over voltage threshold level, which is 11% above the set voltage. If the over voltage condition is caused by a short in high side switch, turning the low side MOSFET on 100% creates an electrical short between the battery and GND, blowing the fuse and disconnecting the battery from the output. DS8203-05 April 2011 Discharge Mode When PRO is low and a transition to standby or shutdown mode occurs, or the output under voltage fault latch is set, the outputs discharge mode is triggered. During discharge mode, there are two paths to discharge the outputs capacitor residual charge during discharge mode. The first is output capacitor discharge to GND through an internal 17Ω switch. The second is output capacitor discharged by forcing the low-side MOSFET turn on/off until PHASEx voltage decrease under 1V. Shutdown Mode Drive EN below the precise EN input falling-edge trip level to place the RT8203 in their low-power shutdown state. When shutdown mode activates, the reference turns off, making the threshold to exit shutdown inaccurate. For automatic shutdown and startup, connect EN to VIN. If PRO is low, both SMPS outputs will enter discharge mode before entering true shutdown. The accurate 1V fallingedge threshold on EN can be used to detect a specific analog voltage level and shutdown the device. Once in shutdown, the 1.6V rising-edge threshold activates, providing sufficient hysteresis for most application. www.richtek.com 19 RT8203 Power-Up Sequencing and On/Off Controls (ONx) Output Inductor Selection ON3 and ON5 control SMPS power-up sequencing. When RT8203 applies in the single channel mode, ON3 or ON5 enables the respective outputs when ONx voltage rising above 2.4V, and disables the respective outputs when ONx voltage falling below 1.3V. The switching frequency (on-time) and operating point (% ripple or LIR) determine the inductor value as follows : Connecting one of ONx to VCC and the other one connecting to VREF can force the latter one output starts after the former one regulates. If both of ONx forced connecting to VREF, both outputs always wait the other one regulating and no one will regulate. Output Voltage Setting (FBx) Connect FBx directly to GND to enable the fixed, preset SMPS output voltages (3.3V and 5V). Connect a resistor voltage-divider at FBx between VOUTx and GND to adjust the respective output voltage between 2V and 5.5V (Figure 6). Choose R2 to be approximately 10kΩ, and solve for R1 using the equation : ⎡ ⎤ VOUTx = VFBx × ⎢1 + ⎛⎜ R1 ⎞⎟ ⎥ R2 ⎠⎦ ⎣ ⎝ where VFBx is 2.0V (typ.). LDO5 connects to VOUT5 through an internal switch only when VOUT5 above the LDO5 automatic switch threshold (4.65V). LDO3 connects to VOUT3 through an internal switch only when VOUT3 is above the LDO3 automatic switch threshold (2.93V). This is the most effective way when the fixed output voltages are used. Once LDOx is supplied from VOUTx, the internal linear regulator turns off. This reduces internal power dissipation and improves efficiency when LDOx is powered with a high input voltage. V IN V OUTx UGATEx L= TON × (VIN - VOUT ) LIR × ILOAD(MAX) Find a low-loss inductor having the lowest possible DC resistance that fits in the allotted dimensions. 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) + [(LIR / 2) x ILOAD(MAX)] This inductor ripple current also impacts transient-response performance, especially at low VIN -VOUTx differences. Low inductor values allow the inductor current to slew faster, replenishing charge removed from the output filter capacitors by a sudden load step. The peak amplitude of the output transient (VSAG) is also a function of the output transient. The (VSAG) also features a function of the maximum duty factor, which can be calculated from the on-time and minimum off-time : V (ΔILOAD )2 × L × (K OUTx +TOFF(MIN) ) VIN VSAG = ⎡ ⎛ VIN - VOUTx ⎞ ⎤ 2 × COUT × VOUTx ⎢K ⎜ ⎟ − TOFF(MIN) ⎥ V IN ⎠ ⎣ ⎝ ⎦ Where the minimum off-time (TOFF (MIN)) = 400ns (typical) and K is from Table 1. Output Capacitor Selection The output filter capacitor must have low enough ESR to meet output ripple and load transient requirements, yet have high enough ESR to satisfy stability requirements. Moreover, the capacitance value must be high enough to absorb the inductor energy going from a full-load to noload condition without tripping the OVP circuit. PHASEx BOOTx R1 VOUTx FBx R2 GND Figure 6. Setting VOUTx with a Resistor-Divider www.richtek.com 20 For CPU core voltage converters and other applications where the output is subject to violent load transients, the output capacitor's size depends on how much ESR is needed to prevent the output from dipping too low under a load transient. Ignoring the sag due to finite capacitance : ESR ≤ VP-P ILOAD(MAX) DS8203-05 April 2011 RT8203 In non-CPU applications, the output capacitor's size depends on how much ESR is needed to maintain an acceptable level of output voltage ripple : VP-P LIR × ILOAD(MAX) ESR ≤ where VP-P is the peak-to-peak output voltage ripple. Organic semiconductor capacitor(s) or specialty polymer capacitor(s) are recommended. For low input-to-output voltage differentials (VIN / VOUTx < 2), additional output capacitance is required to maintain stability and good efficiency in ultrasonic mode. The amount of overshoot due to stored inductor energy can be calculated as : VSOAR = (IPEAK )2 × L 2 × COUT × VOUT where IPEAK is the peak inductor current. indicate the possible presence of loop instability, which is caused by insufficient ESR. Loop instability can result in oscillations at the output after line or load perturbations that can trip the overvoltage protection latch or cause the output voltage to fall below the tolerance limit. 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 helps 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- or overshoot. Layout Considerations Layout is very important in high frequency switching converter design. If designed improperly, the PCB could radiate excessive noise and contribute to the converter instability. Certain points must be considered before starting a layout using the RT8203. Output Capacitor Stability The output capacitor stability is determined by the value of the ESR zero relative to the switching frequency. The point of instability is given by the following equation : fESR = f 1 ≤ SW 2 × π × ESR × COUT 4 Do not put high-value ceramic capacitors directly across the outputs 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 inductor and connecting VOUTx or the FBx divider close to the inductor. Unstable operation manifests itself in two related and distinctly different ways : double-pulsing and feedback loop instability. Double-pulsing 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 a new cycle immediately after the 400ns minimum off-time period has expired. Doublepulsing is more annoying than harmful, resulting in nothing worse than increased output ripple. However, it may DS8203-05 April 2011 ` Connect RC low pass filter from LDO5 to VCC, 1-mF and 10Ω are recommended. Place the filter capacitor close to the IC, within 12mm(0.5 inch) if possible. ` Keep current limit setting network as close as possible to the IC. Routing of the network should avoid coupling to high voltage switching node. ` Connections from the drivers to the respective gate of the high side or the low side MOSFET should be as short as possible to reduce stray inductance. Use 0.65-mm (25 mils) or wider trace. ` All sensitive analog traces and components such as VOUTx, FBx, GND, ONx, PGOOD, ILIMx, VCC, and TON should be placed away from high-voltage switching nodes such as PHASEx, LGATEx, UGATEx, or BOOTx nodes to avoid coupling. Use internal layer(s) as ground plane(s) and shield the feedback trace from power traces and components. ` Gather ground terminal of VIN capacitor(s), VOUTx capacitor(s), and source of low side MOSFETs as close as possible. PCB trace defined as PHASEx node, which connects to source of high side MOSFET, drain of low side MOSFET and high voltage side of the inductor, should be as short and wide as possible. www.richtek.com 21 RT8203 Table 1. TON Setting and PWM Frequency Table VOUT 5 VOUT5 VOUT3 VOUT3 Approximate K-Factor (μs) Frequency (kHz) K-Factor (μs) Frequency (kHz) K-Factor Erro r (%) VCC 4.90 200 3.29 300 ± 10 GND 2.45 400 1.97 500 ± 10 TON Table 2. Operation Mode Truth Table Mode Condition Comment Transitions to discharge mode after a VIN POR and after Power-UP RUN LDOx < UVLO threshold VREF becomes valid. LDO5, LDO3, and VREF remain active. EN = High, ON3 or ON5 enabled Normal Operation. Over Voltage Either output > 111% of nominal Protection Under Voltage Protection level, PRO = Low LGATEx is forced high. LDO3, LDO5 active. Exited by VIN POR or by toggling EN, ON3, or ON5 Either output < 70% of nominal level If PRO is low, both UGATEx and LGATEx are forced low until after 22ms time-out expires and enter discharge mode terminates. LDO3, LDO5 active. output is enabled, PRO = Low Exited by VIN POR or by toggling EN, ON3, or ON5. During discharge mode, there are two paths to discharge the outputs capacitor residual charge during discharge mode. PRO is low and either SMPS output Discharge is still high in either standby mode or shutdown mode Standby Shutdown Thermal Shutdown www.richtek.com 22 The first is output capacitor discharge to GND through an internal 17Ω switch. The second is output capacitor discharged by forcing the low-side MOSFET turn on/off until PHASEx voltage decrease under 1V. ONx < startup threshold, EN = High. LGATEx stays low if PRO is low. LDO3, LDO5 active. EN = Low TJ > 150°C All circuitry off. All circuitry off. Exit by VIN POR or by toggling EN, ON3, or ON5. DS8203-05 April 2011 RT8203 Table 3 Power-Up Sequencing EN (V) VON5 (V) VON3 (V) LDO5 LDO3 5V SMPS 3V SMPS Low X X Off Off Off Off “ >2.4V ” => High Low Low On (after REF powers up) On (after LDO5 powers up) Off Off Low VREF On (after VREF powers up) On (after LDO5 powers up) Off Off Low High On (after VREF powers up) On (after LDO5 powers up) Off On VREF Low On (after VREF powers up) On (after LDO5 powers up) Off Off “ >2.4V ” => High VREF VREF On (after VREF powers up) On (after LDO5 powers up) Off Off “ >2.4V ” => High VREF High On (after VREF powers up) On (after LDO5 powers up) On (after 3V SMPS on) On “ >2.4V ” => High High LOW On (after VREF powers up) On (after LDO5 powers up) On Off “ >2.4V ” => High High VREF On (after VREF powers up) On (after LDO5 powers up) ON On (after 5V SMPS on) “ >2.4V ” => High High High On (after VREF powers up) On (after LDO5 powers up) On On “ >2.4V ” => High “ >2.4V ” => High “ >2.4V ” => High DS8203-05 April 2011 www.richtek.com 23 RT8203 Outline Dimension c D L E E1 e A2 A A1 b Dimensions In Millimeters Dimensions In Inches Symbol Min Max Min Max A 1.346 1.753 0.053 0.069 A1 0.100 0.254 0.004 0.010 A2 1.499 0.059 b 0.203 0.360 0.008 0.014 C 0.178 0.274 0.007 0.011 D 9.800 10.010 0.386 0.394 e 0.635 0.025 E 5.790 6.200 0.228 0.244 E1 3.810 3.990 0.150 0.157 L 0.380 1.270 0.015 0.050 28-Lead SSOP Plastic Package Richtek Technology Corporation Richtek Technology Corporation Headquarter Taipei Office (Marketing) 5F, No. 20, Taiyuen Street, Chupei City 5F, No. 95, Minchiuan Road, Hsintien City Hsinchu, Taiwan, R.O.C. Taipei County, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611 Tel: (8862)86672399 Fax: (8862)86672377 Email: [email protected] Information that is provided by Richtek Technology Corporation is believed to be accurate and reliable. Richtek reserves the right to make any change in circuit design, specification or other related things if necessary without notice at any time. No third party intellectual property infringement of the applications should be guaranteed by users when integrating Richtek products into any application. No legal responsibility for any said applications is assumed by Richtek. www.richtek.com 24 DS8203-05 April 2011