19-1095; Rev 2; 12/97 1-Cell to 3-Cell, High-Power, Low-Noise, Step-Up DC-DC Converters Features ♦ Up to 95% Efficiency (see Typical Output Selector Guide below) ♦ 3.3V Dual Mode™ or 2.7V to 5.5V Adj. Output ♦ 0.7V to 5.5V Input Range ♦ 0.15mW Standby Mode ♦ 300kHz PWM Mode or Synchronizable ♦ Two-Channel ADC with Serial Output ♦ Power-Good Function Applications Digital Cordless Phones PCS Phones Cellular Phones Hand-Held Instruments Palmtop Computers Personal Communicators Local 3.3V to 5V Supplies Ordering Information PART TEMP. RANGE PIN-PACKAGE MAX848ESE -40°C to +85°C 16 Narrow SO MAX849ESE -40°C to +85°C 16 Narrow SO The devices differ only in the current limit of the N-channel MOSFET power switch: 0.8A for the MAX848, and 1.4A for the MAX849. Typical Output Selector Guide VIN (V) 0.9 1.2 2.4 2.7 3.6 VOUT (V) 3.3 5 3.3 5 3.3 5 3.3 5 5 MAX849 IOUT (mA) 100 70 300 200 750 500 800 600 1000 MAX848 IOUT (mA) 70 40 110 70 200 130 250 150 300 Typical Operating Circuit INPUT 0.8V TO 5.5V A/D CHANNEL 1 IN A/D CHANNEL 2 IN A/D CHANNEL SELECT A/D OUTPUT ON/OFF CONTROL SYNC INPUT MAX848 MAX849 AIN1 AIN2 AINSEL DATA ON1 ON2 CLK/SEL POKIN REF LX OUTPUT OUT POUT POK VOLTAGE MONITOR OUTPUT FB GND PGND Pin Configuration appears at end of data sheet. Dual Mode is a trademark of Maxim Integrated Products. ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 408-737-7600 ext. 3468. MAX848/MAX849 General Description The MAX848/MAX849 boost converters set a new standard of high efficiency and high integration for noisesensitive power-supply applications, such as portable phones and small systems with RF data links. The heart of the these devices is a synchronous boost-topology regulator that generates a fixed 3.3V output (or 2.7V to 5.5V adjustable output) from one to three NiCd/NiMH cells or one Li-Ion cell. Synchronous rectification provides a 5% efficiency improvement over similar nonsynchronous boost regulators. In standby mode, pulse-skipping PFM operation keeps the output voltage alive with only 150µW quiescent power consumption. Fixed-frequency PWM operation ensures that the switching noise spectrum is limited to the 300kHz fundamental and its harmonics, allowing easy post-filtering noise reduction. For even tighter noise spectrum control, synchronize to a 200kHz to 400kHz external clock. Battery monitoring is provided by a two-channel, voltage-to-frequency analog-to-digital converter (ADC). One channel is intended for a single-cell battery input (0.625V to 1.875V range), while the other channel is for monitoring higher voltages (0V to 2.5V range). Two control inputs are provided for push-on, push-off control via a momentary pushbutton switch. Upon power-up, an internal comparator monitors the output voltage to generate a power-good output (POK). MAX848/MAX849 1-Cell to 3-Cell, High-Power, Low-Noise, Step-Up DC-DC Converters ABSOLUTE MAXIMUM RATINGS ON1, ON2, OUT, POUT to GND..................................-0.3V, +6V PGND to GND ..........................................................-0.3V, +0.3V LX to PGND ...............................................-0.3V, (VPOUT + 0.3V) CLK/SEL, DATA, POKIN, REF, AINSEL, AIN1, AIN2, FB, POK to GND .....-0.3V, (VOUT + 0.3V) Continuous Power Dissipation (TA = +70°C) Narrow SO (derate 8.7mW/°C above +70°C) ................696mW Operating Temperature Range MAX848ESE/MAX849ESE .................................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature.........................................-65°C to +160°C Lead Temperature (soldering, 10sec) .............................+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 (VOUT = 3.6V, GND = PGND = CLK/SEL = ON1 = ON2 = AINSEL = AIN1 = AIN2 = FB = POKIN, POUT = OUT, TA = 0°C to +85°C, unless otherwise noted.) PARAMETER CONDITIONS MIN Minimum Operating Voltage (Note 1) TYP 0.7 REFERENCE Reference Output Voltage IREF = 0mA REF Load Regulation -1µA < IREF < 50µA REF Supply Rejection 2.5V < VOUT < 5V DC-DC CONVERTER Output Voltage (Note 2) VFB < 0.1V, CLK/SEL = OUT 1.23 VOUT = 3.3V VIN = 1.2V VOUT = 5V VOUT = 3.3V VIN = 2.4V Output Current VOUT = 5V VOUT = 3.3V VIN = 2.7V VOUT = 5V VOUT = 5V 3.17 V 5 15 mV 0.2 5 mV 3.34 3.40 V MAX848 110 MAX849 300 MAX848 70 MAX849 200 MAX848 200 MAX849 750 MAX848 130 MAX849 500 MAX848 250 MAX849 600 MAX848 150 MAX849 800 300 1000 FB Input Current VFB = 1.25V Output Voltage Adjust Range 1.215 V 1.27 MAX849, VIN = 3.6V Adjustable output, CLK/SEL = OUT UNITS 1.25 MAX848, VIN = 3.3V FB Regulation Voltage 1.240 mA mA 1.265 V 200 nA 2.7 5.5 V 2.1 2.4 V Output Voltage Lockout Range (Note 3) Load Regulation (Note 4) CLK/SEL = OUT -1.6 Minimum Start-Up Voltage (Note 5) ILOAD < 1mA, TA > +25°C 0.9 Frequency in Start-Up Mode VOUT = 1.5V Operating Current in Shutdown Current into OUT pin, V ON2 = 3.6V 2 MAX 40 4 _______________________________________________________________________________________ % 1.1 V 300 kHz 20 µA 1-Cell to 3-Cell, High-Power, Low-Noise, Step-Up DC-DC Converters MAX848/MAX849 ELECTRICAL CHARACTERISTICS (continued) (VOUT = 3.6V, GND = PGND = CLK/SEL = ON1 = ON2 = AINSEL = AIN1 = AIN2 = FB = POKIN, POUT = OUT, TA = 0°C to +85°C, unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS µA Operating Current in Low-Power Mode (Note 6) Current into OUT pin, CLK/SEL = GND 35 90 Operating Current in Low-Noise Mode (Note 6) Current into OUT pin, CLK/SEL = OUT, does not include switching losses 150 300 POUT Leakage Current VLX = 0V, V ON2 = VOUT = 5.5V 0.1 20 µA LX Leakage Current VLX = V ON2 = VOUT = 5.5V 0.1 20 µA CLK/SEL = GND 0.3 0.6 CLK/SEL = OUT 0.13 0.25 CLK/SEL = OUT 0.25 0.5 µA DC-DC SWITCHES Switch On-Resistance N-channel P-channel CLK/SEL = OUT N-Channel Current Limit VCLK/SEL = 0V (Note 7) MAX848 600 800 1000 MAX849 1100 1350 1600 MAX848 120 200 300 MAX849 250 400 550 Ω mA ADC Data Output Voltage Low ISINK = 1mA Data Output Voltage High ISOURCE = 1mA VOUT - 0.4 0.4 AIN1 Input Voltage Range AINSEL = GND 0.625 AIN2 Input Voltage Range AINSEL = OUT 0 AIN1, AIN2 Input Current fCLK = 400kHz, VAIN1 = VAIN2 = 2.5V Accuracy fCLK = 400kHz, 5ms conversion, monotonic to 8 bits V V 1.875 1 V 2.5 V 2 µA ±4 % FSR POWER-GOOD Internal Trip Level Rising VOUT, VPOKIN < 0.1V 2.95 3.10 V External Trip Level Rising VPOKIN 1.225 1.275 V POK Low Voltage ISINK = 1mA, VOUT = 3.6V or ISINK = 20µA, VOUT = 1V 0.4 V POK High Leakage Current VOUT = VPOK = 5.5V 1 µA POKIN Leakage Current VPOKIN = 1.5V 50 nA 0.01 LOGIC AND CONTROL INPUTS Input Low Voltage Input High Voltage 1.2V < VOUT < 5.5V, ON1 and ON2 (Note 8) 0.2VOUT VOUT = 2.7V, AINSEL and CLK/SEL 0.2VOUT 1.2V < VOUT < 5.5V, ON1 and ON2 (Note 8) 0.8VOUT VOUT = 5.5V, AINSEL and CLK/SEL 0.8VOUT Logic Input Current ON1, ON2, AINSEL and CLK/SEL Internal Oscillator Frequency CLK/SEL = OUT V 260 300 Oscillator Maximum Duty Cycle 80 85 External Clock Frequency Range 200 CLK/SEL Pulse Width Not tested CLK/SEL Rise/Fall Time Not tested V 1 µA 340 kHz 90 % 400 kHz 200 ns 100 ns _______________________________________________________________________________________ 3 MAX848/MAX849 1-Cell to 3-Cell, High-Power, Low-Noise, Step-Up DC-DC Converters ELECTRICAL CHARACTERISTICS (VOUT = 3.6V, GND = PGND = CLK/SEL = ON1 = ON2 = AINSEL = AIN1 = AIN2 = FB = POKIN, POUT = OUT, TA = -40°C to +85°C, unless otherwise noted.) (Note 9) PARAMETER CONDITIONS MIN TYP MAX UNITS REFERENCE Reference Output Voltage IREF = 0mA 1.225 1.275 V Output Voltage (Note 3) VFB < 0.1V, CLK/SEL = OUT, includes load-regulation error 3.13 3.47 V FB Regulation Voltage Adjustable output, CLK/SEL = OUT 1.21 1.27 V Output Voltage Lockout Range (Note 3) 2.05 2.45 V OUT Supply Current in Shutdown V ON2 = 3.6V 20 µA OUT Supply Current in Low-Power Mode (Note 6) CLK/SEL = GND 90 µA OUT Supply Current in Low-Noise Mode (Note 6) CLK/SEL = OUT, does not include switching losses 300 µA DC-DC CONVERTER DC-DC SWITCHES Switch On-Resistance N-channel P-channel CLK/SEL = OUT N-Channel Current Limit CLK/SEL = GND (Note 7) CLK/SEL = GND 0.6 CLK/SEL = OUT 0.25 CLK/SEL = OUT 0.5 MAX848 600 1100 MAX849 1100 1800 MAX848 120 300 MAX849 250 550 Ω mA ADC Accuracy fCLK = 400kHz, 5ms conversion ±4 % FSR POWER-GOOD Internal Trip Level Rising VOUT, VPOKIN < 0.1V 2.95 3.10 V External Trip Level Rising VPOKIN 1.225 1.275 V 260 340 kHz 80 90 % LOGIC CONTROL INPUTS Internal Oscillator Frequency Oscillator Maximum Duty Cycle CLK/SEL = OUT Note 1: Minimum operating voltage. Because the MAX848/MAX849 are bootstrapped to the output, it will operate down to a 0.7V input. Note 2: In low-power mode (CLK/SEL = GND), the output voltage regulates 1% higher than in low-noise mode (CLK/SEL = OUT or synchronized). Note 3: The part is in start-up mode until it reaches this voltage level. Do not apply full-load current. Note 4: Load regulation is measured from no load to full load, where full load is determined by the N-channel switch current limit. Note 5: Start-up is tested with Figure 2’s circuit. Output current is measured when the input and output voltages are applied. Note 6: Supply current from the 3.34V output is measured between the 3.34V output and the OUT pin. This current correlates directly with actual battery supply current, but is reduced in value according to the step-up ratio and efficiency. VOUT = 3.6V to keep the internal switch open when measuring the current into the device. Note 7: When VCLK/SEL = 0V, the inductor is forced into constant-peak-current, discontinuous operation. This is guaranteed by testing in Figure 2’s circuit. Note 8: ON1 and ON2 inputs have approximately 0.15VOUT hysteresis. Note 9: Specifications to -40°C are guaranteed by design, not production tested. 4 _______________________________________________________________________________________ 1-Cell to 3-Cell, High-Power, Low-Noise, Step-Up DC-DC Converters 70 VIN = 0.9V 60 90 70 PFM PWM 1 10 100 1000 PFM PWM 60 0.1 1 10 100 0.1 1000 10 100 1000 LOAD CURRENT (mA) NO-LOAD BATTERY CURRENT vs. INPUT VOLTAGE SHUTDOWN CURRENT vs. INPUT VOLTAGE START-UP VOLTAGE vs. LOAD CURRENT (VOUT = 3.3V, PWM MODE) TA = +25°C 6 4 TA = -40°C 12 10 TA = +85°C 8 6 TA = +25°C 1.8 4 2 3 4 5 0 6 TA = -40°C 1.2 1.0 TA = +85°C TA = +25°C 1 2 3 5 4 0.6 6 0.01 0.1 1 10 100 INPUT VOLTAGE (V) INPUT VOLTAGE (V) LOAD CURRENT (mA) REFERENCE VOLTAGE vs. TEMPERATURE REFERENCE VOLTAGE vs. REFERENCE CURRENT ADC LINEARITY ERROR vs. FULL-SCALE INPUT VOLTAGE 1.249 1.248 1.246 1.244 1.242 1.238 0 20 40 60 TEMPERATURE (°C) 80 100 AIN2 -0.05 AIN1 -0.15 1.240 1.248 0.15 0.05 1000 MAX848/9 TOC-09 1.250 0.25 LINEARITY ERROR (%FS) 1.250 MAX848/9 TOC-08 1.251 1.252 REFERENCE VOLTAGE (V) MAX848/9 TOC-07 1.252 -20 1.4 TA = -40°C 0 1 1.6 0.8 2 0 MAX848/9 TOC-06 14 2.0 MAX848/9 TOC-05 INCLUDES ALL EXTERNAL COMPONENT LEAKAGES. CAPACITOR LEAKAGE DOMINATES AT TA = +85°C START-UP VOLTAGE (V) 8 18 16 SHUTDOWN CURRENT (µA) MAX848/9 TOC-04 TA = +85°C 10 -40 1 LOAD CURRENT (mA) 12 0 VIN = 0.9V LOAD CURRENT (mA) 14 2 VIN = 1.2V 70 30 0.1 80 PFM PWM 40 40 INPUT CURRENT (mA) VIN = 1.2V 60 VIN = 2.4V 90 50 50 REFERENCE VOLTAGE (V) VIN = 2.4V 80 EFFICIENCY (%) VIN = 1.2V 80 VIN = 3.6V EFFICIENCY (%) EFFICIENCY (%) 90 100 MAX848/9 TOC-02 VIN = 2.4V MAX848 EFFICIENCY vs. LOAD CURRENT (VOUT = 3.3V) 100 MAX848/9 TOC-01 100 MAX849 EFFICIENCY vs. LOAD CURRENT (VOUT = 5V) MAX848/9 TOC-03 MAX849 EFFICIENCY vs. LOAD CURRENT (VOUT = 3.3V) -0.25 0 10 20 30 40 50 60 REFERENCE CURRENT (µA) 70 80 0.1875 0.4375 0.6875 0.9375 FULL-SCALE INPUT VOLTAGE (V) _______________________________________________________________________________________ 5 MAX848/MAX849 Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) MAX848/MAX849 1-Cell to 3-Cell, High-Power, Low-Noise, Step-Up DC-DC Converters Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) HEAVY-LOAD SWITCHING WAVEFORMS (VOUT = 3.3V) LINE-TRANSIENT RESPONSE MAX848/9 TOC-11 MAX848/9 TOC-10 VOUT A 0V A B 0V 0A B C 5ms/div 1µs/div VIN = 1.1V, IOUT = 200mA, VOUT = 3.3V IOUT = 0mA, VOUT = 3.3V A = LX VOLTAGE, 2V/div B = INDUCTOR CURRENT, 0.5A/div C = VOUT RIPPLE, 50mV/div, AC COUPLED A = VIN, 1.1V TO 2.1V, 1V/div B = VOUT RIPPLE, 50mV/div, AC COUPLED POWER-ON DELAY (PFM MODE) LOAD-TRANSIENT RESPONSE MAX848/9 TOC-13 MAX848/9 TOC-12 3.3V A A 0A B C B 2ms/div VIN = 1.1V, VOUT = 3.3V A = LOAD CURRENT, 0mA TO 200mA, 0.2A/div B = VOUT RIPPLE, 50mV/div, AC COUPLED 6 200mA 0mA 5ms/div A = VON1, 2V/div B = VOUT, 1V/div C = INPUT CURRENT, 0.2A/div _______________________________________________________________________________________ 1-Cell to 3-Cell, High-Power, Low-Noise, Step-Up DC-DC Converters MAX849 DECT LOAD-TRANSIENT RESPONSE MAX849 GSM LOAD-TRANSIENT RESPONSE MAX848/9 TOC-15 MAX848/9 TOC-14 3.3V 5V A A B B 0A 0A 2ms/div 1ms/div VIN = 3.6V, VOUT = 5V, COUT = 440µF VIN = 1.2V, VOUT = 3.3V, COUT = 440µF A = VOUT RIPPLE, 200mV/div, AC COUPLED B = LOAD CURRENT, 100mA TO 1A, 0.5A/div, PULSE WIDTH = 577µs A = VOUT RIPPLE, 200mV/div, AC COUPLED B = LOAD CURRENT, 50mA TO 400mA, 0.2A/div, PULSE WIDTH = 416µs MAX849 NOISE SPECTRUM (VOUT = 3.3V, VIN = 1.2V, RLOAD = 50Ω) NOISE (mVRMS) MAX848/9 TOC-16 2.7 0 0.1k 1k 10k 100k 1M FREQUENCY (Hz) MAX849 INTERNAL OSCILLATOR FREQUENCY vs. TEMPERATURE VOUT = 5V 340 320 VOUT = 3.3V 300 MAX848/9 TOC-18 360 2.0 1.8 PEAK INDUCTOR CURRENT (A) MAX848/9 TOC-17 INTERNAL OSC. FREQUENCY (kHz) 380 MAX849 PEAK INDUCTOR CURRENT vs. OUTPUT VOLTAGE 1.7 1.6 1.5 1.4 1.3 1.2 280 -40 -20 0 20 40 60 TEMPERATURE (°C) 80 100 2.5 3.0 3.5 4.0 4.5 5.0 5.5 OUTPUT VOLTAGE (V) _______________________________________________________________________________________ 7 MAX848/MAX849 Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) 1-Cell to 3-Cell, High-Power, Low-Noise, Step-Up DC-DC Converters MAX848/MAX849 Pin Description 8 PIN NAME FUNCTION 1 AIN1 ADC’s Channel 1 Input. Analog input voltage range is 0.625V to 1.875V. 2 AIN2 ADC’s Channel 2 Input. Analog input voltage range is 0V to 2.5V. 3 REF Reference Output. Bypass with a 0.22µF capacitor to GND. 4 GND Ground. Use for low-current ground paths. Connect to PGND with a short trace. 5 OUT Output Sense Input. The IC is powered from OUT. Bypass to GND with a 0.1µF ceramic capacitor. Connect OUT to POUT through a 10Ω series resistor. 6 POKIN Power-Good Comparator Input. Connect to GND for fixed threshold (VOUT x 0.9). To adjust the threshold, connect to a resistor divider from OUT to GND. 7 FB Dual Mode DC-DC Converter Feedback Input. Connect to GND for fixed 3.3V output voltage. Connect to a resistor divider from OUT to GND to adjust the output voltage. Minimize noise coupling from switching signals to FB. 8 POK Power-Good Output. This open-drain output is pulled low when the output voltage (VOUT) drops below the internally set threshold (fixed threshold), or when the voltage at POKIN drops below VREF (adjustable threshold). 9 AINSEL 10 DATA ADC’s Input Channel Selector. Pull low to select AIN1 and drive high to select AIN2. ADC’s Serial Output. Pulsed output, RZ format. Full scale is fOSC/2 (fCLK/2 in external sync mode). The DATA output is low when VCLK/SEL = 0V (PFM mode). External Clock Input/Regulator’s Switching Mode Selector. CLK/SEL = low: low-power, low-quiescent PFM mode. Delivers 100mW of output power. CLK/SEL = high: low-noise, high-power PWM mode, switching at a constant frequency (300kHz). CLK/SEL = driven with external clock: low-noise, high-power, synchronized PWM mode. The internal oscillator is synchronized to the external clock (200kHz ~ 400kHz). Turning the DC-DC converter on with VCLK/SEL = 0V also serves as a soft-start function, since the peak inductor current is limited to 30% of the nominal value. 11 CLK/SEL 12 PGND 13 LX 14 POUT 15 ON2 OFF Control Input. When ON1 = 0 and ON2 = 1, the IC is off. 16 ON1 ON Control Input. When ON1 = 1 or ON2 = 0, the IC is on. Source of the Internal N-Channel Power MOSFET. Connect to high-current ground path. Drain of the Internal N-Channel Power MOSFET and P-Channel Synchronous Rectifier Source of the Internal P-Channel Synchronous Rectifier MOSFET. Connect an external Schottky diode from LX to POUT. Bypass to PGND with a 0.1µF ceramic capacitor as close to the IC as possible. _______________________________________________________________________________________ 1-Cell to 3-Cell, High-Power, Low-Noise, Step-Up DC-DC Converters MAX848/MAX849 OUT MAX848/MAX849 START-UP OSCILLATOR 2.25V EN POUT Q Q D PCH 0.25Ω ON1 ON ON2 REF 1.25V RDY REF EN CLK/SEL FB FEEDBACK AND POWER-GOOD SELECT POKIN Q OSC 300kHz OSCILLATOR GND LX EN PFM/PWM FEEDBACK NCH 0.13Ω PGND MODE PFM/PWM CONTROLLER POK N EN AINSEL AIN1 ADC DATA AIN2 Figure 1. Functional Diagram _______________Detailed Description The MAX848/MAX849 combine a switching regulator, N-channel power MOSFET, P-channel synchronous rectifier, precision reference voltage, power-good indicator, and battery voltage monitor, all in a single monolithic device. The MAX848/MAX849 are powered directly from the output. The output voltage is factory preset to 3.3V or adjustable from 2.7V to 5V with external resistors (Dual Mode™ operation). These devices start from a low 1V input voltage and remain operational down to 0.7V. The MAX848/MAX849 operate with either one to three NiCd/NiMH cells or one Li-Ion cell. At power-up, an internal low-voltage oscillator drives the N-channel power switch, and the output voltage slowly builds up. The oscillator has a 25% nominal duty cycle to prevent current build-up in the inductor. An output voltage in excess of the nominal 2.25V lockout voltage activates the error comparator and internal timing circuitry. The device resumes operation in either pulse-frequency-modulation (PFM) low-power mode or pulse-width-modulation (PWM) low-noise mode, selected by the logic control, CLK/SEL. Figure 2 shows the standard application circuit for the MAX849 configured in the high-power PWM mode. On/Off Control The MAX848/MAX849 are turned on or off by logic input pins ON1 and ON2 (Table 1). When ON1 = 1 or ON2 = 0, the part is on. When ON1 = 0 and ON2 = 1, the part is off. Both inputs have logic trip points near 0.5 x VOUT with 0.15 x VOUT hysteresis. Table 1. On/Off Logic Control ON1 0 ON2 0 0 1 Off 1 0 On 1 1 On MAX848/MAX849 On Operating Modes The MAX848/MAX849 operate in either PFM, PWM, or PWM synchronized to an externally applied clock signal. Table 2 lists each operating mode. _______________________________________________________________________________________ 9 MAX848/MAX849 1-Cell to 3-Cell, High-Power, Low-Noise, Step-Up DC-DC Converters VIN = 1.1V OUT C2 0.1µF D LOGIC HIGH POUT 10Ω R3 100k Q * POUT 3.3V @ 200mA D1 MBR0520L MAX849 GND POK ON1 C5 0.1µF R C4 2 x 100µF L1 10µH C1 22µF LX CLK/SEL PGND C3 FB 0.22µF POKIN REF ON2 LX FEEDBACK S N Q REF R PFM-MODE CURRENTLIMIT LEVEL CURRENT SENSE PGND * HEAVY LINES INDICATE HIGH-CURRENT PATH. Figure 2. 3.3V Preset Output Figure 3. Controller Block Diagram in PFM Mode Table 2. Selecting Operating Mode CLK/SEL MODE 0 PFM 1 PWM External clock (200kHz ~ 400kHz) Synchronized PWM Low-Power PFM Mode When CLK/SEL is pulled low, the MAX848/MAX849 operate in low-power, low-supply-current PFM mode. Pulsefrequency modulation provides the highest efficiency at light loads. The P-channel rectifier is turned off to reduce gate-charge losses, and the regulator operates in discontinuous mode. The N-channel power MOSFET is kept on until the inductor current ramps to 30% of the current limit. The inductor energy is delivered to the output capacitor when the switch turns off. A new cycle is inhibited until the inductor current crosses zero. Zero current detection is accomplished by sensing the LX voltage crossing the output voltage. Figure 3 shows the block diagram for the PFM controller. Low-Noise PWM Mode When CLK/SEL is pulled high, the MAX848/MAX849 operate in high-power, low-noise, current-mode PWM, switching at the 300kHz nominal internal oscillator frequency. The internal rectifier is active in this mode, and the regulator operates in continuous mode. The N-channel power MOSFET turns on until either the output voltage is in regulation or the inductor current limit is reached (0.8A for the MAX848 and 1.4A for the MAX849). The switch turns off for the remainder of the cycle and the inductor energy is delivered to the output 10 capacitor. A new cycle is initiated on the next oscillator cycle. In low-noise applications, the fundamental and the harmonics generated by the fixed switching frequency can easily be filtered. Figure 4 shows the block diagram for the PWM controller. The MAX848/MAX849 enter synchronized current-mode PWM when a clock signal (200kHz < fCLK < 400kHz) is applied to CLK/SEL. The internal synchronous rectifier is active and the switching frequency is synchronized to the externally applied clock signal. For wireless applications, this ensures that the harmonics of the switching frequencies are predictable and can be kept outside the IF band(s). High-frequency operation permits low-magnitude output ripple voltage. The MAX848/MAX849 are capable of providing a stable output even with a rapidly pulsing load (GSM, DECT), such as from a transmitter power amplifier in digital cordless phones (see Typical Operating Characteristics). In PWM mode, the use of the synchronous rectifier ensures constant-frequency operation, regardless of the load current. Setting the Output Voltage Externally The MAX848/MAX849 feature Dual Mode operation. The output voltage is preset to 3.3V (FB = 0V), or it can be adjusted from 2.7V to 5.5V with external resistors R1, R2, and R3, as shown in Figure 5. To set the output voltage externally, select resistor R3 in the 10kΩ to 100kΩ range. The values for R1 and R2 are given by: R2 = R3(VOUT / VTRIP - 1) R1 = (R3 + R2)(VTRIP / VREF - 1) ______________________________________________________________________________________ 1-Cell to 3-Cell, High-Power, Low-Noise, Step-Up DC-DC Converters MAX848/MAX849 POUT P OUT FEEDBACK MAX848 MAX849 REF LX R Q OUTPUT R1 POKIN N R2 S FB GND PGND POK R3 PWM-MODE CURRENTLIMIT LEVEL OSC Figure 4. Controller Block Diagram in PWM Mode where VREF = 1.25V, VOUT is the desired output voltage, and VTRIP is the desired trip level for the powergood comparator. Power-OK The MAX848/MAX849 feature a power-good comparator. This comparator’s open-drain output, POK, is pulled low when the output voltage falls below the nominal internal threshold level of 3V with POKIN = 0V. To set the power-good trip level externally, refer to the Setting the Output Voltage Externally section. Figure 5. Adjustable Output Voltage and Power-Good Trip Level AIN1 AINSEL C C AIN2 Q 2 x REF REF Analog-to-Digital Converter (ADC) The MAX848/MAX849 have an internal, two-channel, serial ADC. The ADC converts an analog input voltage into a digital stream available at the DATA pin. The converter skips clock pulses in proportion to the input voltage. Output format is a return-to-zero bit stream with a bit duration of 1/fCLK. At zero-scale input voltage, all pulses are skipped and DATA remains low; with a positive fullscale input voltage, no pulses are skipped; and at midscale, every other pulse is skipped. The ADC’s clock is one-half of the externally applied clock signal or one-half of the internal 300kHz clock available at LX. In PFM mode, the converter is not active and DATA is driven low. Channel 1, AIN1, has an input voltage range of 0.625V to 1.875V and is selected when AINSEL is low. Channel 2, AIN2, accepts inputs in the 0V to 2.5V range and is selected when AINSEL is pulled high (Figure 6). The ADC is a switched-capacitor type; therefore, an anti-aliasing filter might be required at the inputs. Insert a 1kΩ series resistor and a 0.01µF filter capacitor in noisy environments. D C/2 C/2 OSC ÷2 DATA Figure 6. A/D Converter Block Diagram Timer Function Implementation Implement the necessary counter functions either with discrete hardware or with microcontroller (µC) implementations. The output resolution depends on how many of the ADC clock pulses are counted, as shown in Figure 7. Hardware Implementation A complete hardware solution can be implemented using either two counters or an ASIC. Resolution depends on how many pulses are counted. The main advantage of the discrete hardware implementation is that accuracy is not affected by interrupt latency associated with the µC solution. ______________________________________________________________________________________ 11 MAX848/MAX849 1-Cell to 3-Cell, High-Power, Low-Noise, Step-Up DC-DC Converters COUNTING FOUR PULSES fOSC/2 DATA GIVES YOU 2-BIT RESOLUTION Figure 7. Bit Stream at 1/2 Full Scale When using two counters of the same length, as shown in Figure 8, one counter (A) just counts the A/D clock pulses (fOSC/2), and the other counter (B) counts DATA output pulses. When counter A overflows (for example, after 256 clock cycles for an 8-bit counter), counter B is disabled. The controller reads the counter B output data and calculates the analog voltage present at the ADC’s input. All µC Implementation This implementation uses a µC timer and a counter. The timer and the counter are reset at the same time. The counter counts data-output pulses applied at its input. When the timer times out, an interrupt is asserted. The µC then reads the state of the counter register. The interrupt-handling overhead can cause the counter to count more pulses than desired. Accuracy depends on how long the µC needs to read the counter. No errors will occur if the counter is disabled within one clock period. Interrupt latency reduces accuracy. The main advantage of this implementation is that no external hardware is required. __________________Design Procedure Inductor Selection The MAX848/MAX849’s high switching frequency allows the use of a small inductor. Use a 10µH inductor for the MAX849 and a 22µH inductor for the MAX848. Inductors with a ferrite core or equivalent are recommended; powder iron cores are not recommended for use with high switching frequencies. Make sure the inductor’s saturation rating (the current at which the core begins to saturate and inductance starts to fall) exceeds the internal current limit: 0.8A for the MAX848 and 1.4A for the MAX849. However, it is generally acceptable to bias the inductor into saturation by approximately 20% (the point where the inductance is 20% below the nominal value). For highest efficiency, use a coil with low DC resistance, preferably under 100mΩ. To minimize radiated noise, use a toroid, pot core, or shielded inductor. See Table 5 for a list of suggested inductor suppliers. 12 VCC CLOCK/SEL OR LX A ÷2 EN CLK CLR CLEAR DATA OUTPUT CARRY OUTPUT 8-BIT COUNTER RC B CLR CLK 8-BIT COUNTER EN LATCH Figure 8. Discrete Hardware Solution for Counting A/D Output Data Pulses Diode Selection The MAX848/MAX849’s high switching frequency demands a high-speed rectifier. Schottky diodes, such as the 1N5817 or MBR0520L, are recommended. Make sure the diode’s current rating exceeds the maximum load current and that its breakdown voltage exceeds VOUT. The Schottky rectifier diode carries load currents only in the PFM operating mode, since the P-channel synchronous rectifier is disabled. Therefore, the current rating need not be high (0.5A is sufficient). In PFM mode, the voltage drop across the rectifier diode causes efficiency loss. However, when operating in PWM mode, the internal P-channel synchronous rectifier is active and efficiency loss due to the rectifier diode is minimized. For high-temperature applications, Schottky diodes may be inadequate due to their high leakage currents; use high-speed silicon diodes such as the MUR105 or EC11FS1. At heavy loads and high temperatures, the benefits of a Schottky diode’s low forward voltage may outweigh the disadvantage of high leakage current. See Table 4 for a list of suggested diode suppliers. ______________________________________________________________________________________ 1-Cell to 3-Cell, High-Power, Low-Noise, Step-Up DC-DC Converters µC MAX848 MAX849 ON2 OUT VDD I/O MAX848 MAX849 I/O ON1 MAX8865/MAX8866 DUALS MAX8863/MAX8864 SINGLES PA µC 1MΩ Figure 9. Momentary Pushbutton On/Off Switch RADIO Figure 10. Typical Phone Application Applications Information Capacitor Selection Input Bypass Capacitors A 22µF, low-ESR input capacitor will reduce peak currents and reflected noise due to inductor current ripple. Smaller ceramic capacitors may also be used for light loads or in applications that can tolerate higher input ripple. Output Filter Capacitors Two 100µF (single 100µF for the MAX848), 10V, lowESR, output filter capacitors typically exhibit 30mV ripple when stepping up from 1.2V to 3.3V at 200mA (100mA for the MAX848). Bypass the MAX848/MAX849 supply input, OUT, with a 0.1µF ceramic capacitor to GND. Also bypass POUT to PGND with a 0.1µF ceramic capacitor. The filter capacitors’ equivalent series resistance (ESR) affects efficiency and output ripple. The output voltage ripple is the product of the peak inductor current and the output capacitor’s ESR. Low-ESR, surface-mount tantalum capacitors are currently available from Sprague (595D series) and AVX (TPS series). Sanyo OS-CON organic-semiconductor, through-hole capacitors also exhibit very low ESR, and are especially useful for operation at cold temperatures. See Table 5 for a list of suggested capacitor suppliers. Using a Momentary On/Off Switch A momentary pushbutton switch can be used to turn the MAX848/MAX849 on and off. As shown in Figure 9, ON1 is pulled low and ON2 is pulled high when the part is off. When the momentary switch is pressed, ON2 is pulled low and the regulator turns on. The switch should be on long enough for the µC to exit reset. The controller issues a logic high to ON1, which guarantees that the part will stay on, regardless of the switch state. To turn off the regulator, the switch is pressed and held. The controller reads the switch status and pulls ON1 low. The switch is released and ON2 is pulled high. Power Amplifier (PA) and Radio Supply in a Typical Phone Application The MAX849 is an ideal power supply for the power amplifier (PA) and the radio used in digital cordless and PCS phones (Figure 10). The PA is directly powered by the MAX849 for maximum output swing. Postlinear regulators power the controller and the radio. In addition, they reduce switching noise and ripple. Table 3 lists the output power available when operating with one or more NiCd/NiMH cells or one Li-Ion cell. Table 3. Available Output Power INPUT VOLTAGE (V) OUTPUT VOLTAGE: PA POWER SUPPLY (V) OUTPUT POWER (W) 1 NiCd/NiMH 1.2 3.3 0.9 2 NiCd/NiMH 2.4 3.3 2.4 2 NiCd/NiMH 2.4 5.0 2.6 3 NiCd/NiMH or 1 Li-Ion 3.6 5.0 4.3 NUMBER OF CELLS ______________________________________________________________________________________ 13 MAX848/MAX849 1MΩ MAX848/MAX849 1-Cell to 3-Cell, High-Power, Low-Noise, Step-Up DC-DC Converters the timing resistor should not exceed the difference between the output voltage and the µC reset threshold voltage. This resistor should be large enough to minimize the shutdown current. µC MAX848 MAX849 OUT VCC µC-Controlled Shutdown The MAX848/MAX849 turn on when ON1 = 1 or ON2 = 0. The µC monitors the battery voltage and turns off the device (forces ON1 low and ON2 high) when the battery is weak. R RESET POK C Layout Considerations Figure 11. Power-On Reset Delay Power-On Reset Delay Adding a timing capacitor from POK to GND generates a power-on reset delay. The reset time constant is determined by the pull-up resistor and timing capacitor (Figure 11). When power is turned on, POK is low and the capacitor is shorted. When the output voltage reaches regulation, POK goes high and the capacitor slowly charges to the output voltage. The timing resistor value depends on the controller’s RESET input leakage current. The voltage drop across Due to high inductor current levels and fast switching waveforms, which radiate noise, proper PC board layout is essential. Protect sensitive analog grounds by using a star ground configuration. Minimize ground noise by connecting PGND, the input bypass capacitor ground lead, and the output filter capacitor ground lead to a single point (star ground configuration). Also, minimize lead lengths to reduce stray capacitance and trace resistance. If an external resistor divider is used to set the output voltage (Figure 5), the trace from FB to the resistors must be extremely short and must be shielded from switching signals, such as CLK, DATA, or LX. Table 4. Component Selection Guide PRODUCTION INDUCTORS CAPACITORS Surface Mount Sumida CDR63B, CD73, CDR73B, CD74B series Coilcraft DO1608, DO3308, DT3316 series Matsuo 267 series Sprague 595D series AVX TPS series Through Hole Sumida RCH654 series Sanyo OS-CON series Nichicon PL series Table 5. Component Suppliers SUPPLIER PHONE Motorola MBR0520L Motorola 1N5817 Chip Information FAX AVX USA: 803-946-0690 800-282-4975 803-626-3123 Coilcraft USA: 847-639-6400 847-639-1469 Matsuo USA: 714-969-2491 714-960-6492 Motorola USA: 602-303-5454 602-994-6430 Sanyo USA: 619-661-6835 Japan: 81-7-2070-6306 619-661-1055 81-7-2070-1174 Sumida USA: 847-956-0666 Japan: 81-3-3607-5111 847-956-0702 81-3-3607-5144 14 DIODES TRANSISTOR COUNT: 2059 ______________________________________________________________________________________ 1-Cell to 3-Cell, High-Power, Low-Noise, Step-Up DC-DC Converters MAX848/MAX849 Pin Configuration TOP VIEW AIN1 1 16 ON1 AIN2 2 15 ON2 REF 3 14 POUT GND 4 OUT 5 MAX848 MAX849 13 LX 12 PGND 11 CLK/SEL POKIN 6 10 DATA FB 7 9 POK 8 AINSEL Narrow SO SOICN.EPS Package Information ______________________________________________________________________________________ 15 MAX848/MAX849 1-Cell to 3-Cell, High-Power, Low-Noise, Step-Up DC-DC Converters NOTES 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. 16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.