Datasheet MAX1771 (Maxim) - 8
| Manufacturer | Maxim |
| Description | 12V or Adjustable, High-Efficiency, Low IQ, Step-Up DC-DC Controller |
| Pages / Page | 16 / 8 — 12V or Adjustable, High-Efficiency, Low IQ, Step-Up DC-DC Controller. for … |
| File Format / Size | PDF / 782 Kb |
| Document Language | English |
12V or Adjustable, High-Efficiency, Low IQ, Step-Up DC-DC Controller. for fixed-output operation. External resistors must
Model Line for this Datasheet
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MAX1771
12V or Adjustable, High-Efficiency, Low IQ, Step-Up DC-DC Controller
VIN = 5V VIN = 5V C1 C2 C2 68µF 0.1µF 0.1µF 2 2 L1 V+ V+ 22µH 5 C1 5 D1 VOUT = 12V REF REF 1N5817-22 AT 0.5A 68µF C3 C3 MAX1771 L1 MAX1771 0.1 0.1 µF 22 µF C4 µH D1 4 VOUT = 12V 4 1 SHDN SHDN EXT 300µF 1N5817-22 N AT 0.5A MTD20N03HDL 3 1 6 8 FB N EXT AGND CS RSENSE R2 Si9410DY/ 40mΩ 127k MTD20N03HDL Ω 8 3 6 AGND CS FB R C4 GND SENSE R1 GND 40mΩ 300µF 7 18kΩ C5 7 100pF VOUT R2 = (R1) ( -1) VREF VREF = 1.5V Figure 2a. 12V Preset Output, Bootstrapped Figure 2b. 12V Output, Non-Bootstrapped
for fixed-output operation. External resistors must
VIN = 4V
be used to set the output voltage.
Use 1% external C2 feedback resistors when operating in adjustable-output 0.1µF C1 mode (Figures 2b, 2c) to achieve an overall output volt- 2 L1 47µF age accuracy of ±5%. To achieve highest efficiency, V+ 22µH 5 D1 operate in bootstrapped mode whenever possible. REF 1N5817-22 VOUT = 9V C3 MAX1771
External Power-Transistor
0.1µF 4 1 C4 SHDN EXT
Control Circuitry
N 200µF Si9410DY/
PFM Control Scheme
6 8 MTD20N03HDL The MAX1771 uses a proprietary current-limited PFM AGND CS RSENSE control scheme to provide high efficiency over a wide R2 40mΩ 140kΩ range of load currents. This control scheme combines the 3 FB ultra-low supply current of PFM converters (or pulse skip- GND R1 pers) with the high full-load efficiency of PWM converters. 7 28kΩ C5 Unlike traditional PFM converters, the MAX1771 uses a VOUT 100pF R2 = (R1) ( -1) sense resistor to control the peak inductor current. The VREF device also operates with high switching frequencies VREF = 1.5V (up to 300kHz), allowing the use of miniature external Figure 2c. 9V Output, Bootstrapped components. As with traditional PFM converters, the power transistor increases at low input voltages. However, the supply is not turned on until the voltage comparator senses current is also reduced because V+ is at a lower volt- the output is out of regulation. However, unlike tradition- age, and because less energy is consumed while al PFM converters, the MAX1771 switch uses the com- charging and discharging the external MOSFET’s gate bination of a peak current limit and a pair of one-shots capacitance. The minimum input voltage is 3V when that set the maximum on-time (16µs) and minimum off- using external feedback resistors. With supply voltages time (2.3µs); there is no oscillator. Once off, the mini- below 5V, bootstrapped mode is recommended. mum off-time one-shot holds the switch off for 2.3µs.
Note: When using the MAX1771 in non-boot-
After this minimum time, the switch either 1) stays off if
strapped mode, there is no preset output operation
the output is in regulation, or 2) turns on again if the
because V+ is also the output voltage sense point
output is out of regulation. 8 Maxim Integrated
12V or Adjustable, High-Efficiency, Low IQ, Step-Up DC-DC Controller
VIN = 5V VIN = 5V C1 C2 C2 68µF 0.1µF 0.1µF 2 2 L1 V+ V+ 22µH 5 C1 5 D1 VOUT = 12V REF REF 1N5817-22 AT 0.5A 68µF C3 C3 MAX1771 L1 MAX1771 0.1 0.1 µF 22 µF C4 µH D1 4 VOUT = 12V 4 1 SHDN SHDN EXT 300µF 1N5817-22 N AT 0.5A MTD20N03HDL 3 1 6 8 FB N EXT AGND CS RSENSE R2 Si9410DY/ 40mΩ 127k MTD20N03HDL Ω 8 3 6 AGND CS FB R C4 GND SENSE R1 GND 40mΩ 300µF 7 18kΩ C5 7 100pF VOUT R2 = (R1) ( -1) VREF VREF = 1.5V Figure 2a. 12V Preset Output, Bootstrapped Figure 2b. 12V Output, Non-Bootstrapped
for fixed-output operation. External resistors must
VIN = 4V
be used to set the output voltage.
Use 1% external C2 feedback resistors when operating in adjustable-output 0.1µF C1 mode (Figures 2b, 2c) to achieve an overall output volt- 2 L1 47µF age accuracy of ±5%. To achieve highest efficiency, V+ 22µH 5 D1 operate in bootstrapped mode whenever possible. REF 1N5817-22 VOUT = 9V C3 MAX1771
External Power-Transistor
0.1µF 4 1 C4 SHDN EXT
Control Circuitry
N 200µF Si9410DY/
PFM Control Scheme
6 8 MTD20N03HDL The MAX1771 uses a proprietary current-limited PFM AGND CS RSENSE control scheme to provide high efficiency over a wide R2 40mΩ 140kΩ range of load currents. This control scheme combines the 3 FB ultra-low supply current of PFM converters (or pulse skip- GND R1 pers) with the high full-load efficiency of PWM converters. 7 28kΩ C5 Unlike traditional PFM converters, the MAX1771 uses a VOUT 100pF R2 = (R1) ( -1) sense resistor to control the peak inductor current. The VREF device also operates with high switching frequencies VREF = 1.5V (up to 300kHz), allowing the use of miniature external Figure 2c. 9V Output, Bootstrapped components. As with traditional PFM converters, the power transistor increases at low input voltages. However, the supply is not turned on until the voltage comparator senses current is also reduced because V+ is at a lower volt- the output is out of regulation. However, unlike tradition- age, and because less energy is consumed while al PFM converters, the MAX1771 switch uses the com- charging and discharging the external MOSFET’s gate bination of a peak current limit and a pair of one-shots capacitance. The minimum input voltage is 3V when that set the maximum on-time (16µs) and minimum off- using external feedback resistors. With supply voltages time (2.3µs); there is no oscillator. Once off, the mini- below 5V, bootstrapped mode is recommended. mum off-time one-shot holds the switch off for 2.3µs.
Note: When using the MAX1771 in non-boot-
After this minimum time, the switch either 1) stays off if
strapped mode, there is no preset output operation
the output is in regulation, or 2) turns on again if the
because V+ is also the output voltage sense point
output is out of regulation. 8 Maxim Integrated
