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MAX711ESE Datasheet(PDF) 6 Page - Maxim Integrated Products |
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MAX711ESE Datasheet(HTML) 6 Page - Maxim Integrated Products |
6 / 12 page _______________Detailed Description The MAX710/MAX711 integrate a step-up DC-DC con- verter with a linear regulator to provide step-up/down voltage conversion. The step-up switch-mode regulator contains an N-channel power MOSFET switch. It also shares a precision voltage reference with a linear regu- lator that contains a P-channel MOSFET pass element (Figure 1). Step-Up Operation A pulse-frequency-modulation (PFM) control scheme with a constant 1µs off-time and variable on-time con- trols the N-channel MOSFET switch. The N-channel switch turns off when the part reaches the peak current limit or the 4µs maximum on-time. The ripple frequency is a function of load current and input voltage. Step-Down Operation The low-dropout linear regulator consists of a refer- ence, an error amplifier, and a P-channel MOSFET. The reference is connected to the error amplifier’s inverting input. The error amplifier compares this reference with the selected feedback voltage and amplifies the differ- ence. The difference is conditioned and applied to the P-channel pass transistor’s gate. Operating Configurations The MAX710/MAX711 have several operating configu- rations to minimize noise and optimize efficiency for dif- ferent input voltage ranges. These configurations are accomplished via the N/E input, which controls opera- tion of the on-chip linear regulator. With N/E low, the linear regulator behaves as a 0.7 Ω (at 5V output) PFET switch when the IC is boosting, and as a conventional linear regulator when VIN > VOUT. This provides optimum boost efficiency, but the PFET does little to reject boost-converter output ripple. With N/E high, boost ripple rejection is optimized by maintaining headroom (VFV, typically 0.5V at 5V output) across the linear regulator. Boost mode efficiency is then about 10% lower than with N/E high. 3.3V/5V or Adjustable, Step-Up/Down DC-DC Converters 6 _______________________________________________________________________________________ ______________________________________________________________Pin Description Drain Connection for internal N-channel power MOSFET LX 1 Power Ground PGND 2 Shutdown Input. When low, the entire circuit is off and OUT is actively pulled to GND. SHDN 4 Inductor Current-Limit-Select Input. Connect to GND for 1.5A limit and to PS for 0.8A limit. ILIM 3 Standby Input. Connect to GND to disable boost circuit. Connect to PS for normal operation. STBY 5 Selects low-noise or high-efficiency mode. Connect to GND for high efficiency and to PS for lowest noise. See Operating Configurations section. N/E 7 Selects the output voltage. Connect to GND for 5V output and to OUT for 3.3V output. 3/5 6 2 4 3 5 7 — 1 Low-Battery Comparator Output LBO 8 8 Negative Input to Low-Battery Comparator LBI- 10 Source of internal PFET regulator. The IC is powered from PS. PS 12 Positive Input to Low-Battery Comparator LBI+ 11 1.28V Reference Voltage Output. Bypass with a 0.1µF capacitor to GND. REF 13 Power Ground PGND 15 Analog Ground. Must be low impedance. Solder directly to ground plane. GND 14 10 12 11 13 15 14 9 Drain Connection for internal N-channel power MOSFET LX 16 16 Linear-Regulator Output. Bypass with a 4.7µF capacitor to GND. OUT 9 MAX711 MAX710 FUNCTION NAME PIN Feedback Input FB — 6 |
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