MAX863EEE 查看數據表（PDF） - Maxim Integrated

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MAX863EEE

Dual, High-Efficiency, PFM, Step-Up DC-DC Controller

Maxim Integrated 

Dual, High-Efficiency, PFM, Step-Up

DC-DC Controller

______________________________________________________________Pin Description

PIN

NAME

FUNCTION

1

SENSE1 Feedback Input for DC-DC Controller 1 in Fixed-Output Mode

2

VDD

IC Power-Supply Input

Adjustable Feedback and Preset Output Voltage Selection Input for DC-DC Controller 1. Connect to VDD

3

FB1

for 3.3V preset output or to GND for 5V output. Connect a resistor voltage divider to adjust the output volt-

age. See the section Set the Output Voltage.

Bootstrap Low-Voltage-Oscillator Enable Input. BOOT is an active-high, logic-level input. It enables the

4

BOOT

low-voltage oscillator to allow start-up from input voltages down to 1.5V while in a bootstrapped circuit

configuration. Connect BOOT to GND when in a non-bootstrapped configuration. If BOOT is high, VDD

must be connected to OUT1.

5

CS1

Input to the Current-Sense Comparator of DC-DC Controller 1

6

EXT1

Gate-Drive Output of DC-DC Controller 1. Drives an external N-channel power MOSFET.

7

GND

Analog Ground for Internal Reference, Feedback, and Control Circuits

8

PGND High-Current Ground Return for Internal MOSFET Drivers

9

EXT2

Gate-Drive Output of DC-DC Controller 2. Drives an external N-channel power MOSFET.

10

CS2

Input to the Current-Sense Amplifier of DC-DC Controller 2

11

SHDN1 Active-Low Shutdown Input for DC-DC Controller 1. Connect to VDD for normal operation.

12

FB2

Adjustable Feedback Input for DC-DC Controller 2. Connect a resistor voltage divider to adjust the output

voltage. See the section Set the Output Voltage.

13

LBO

Low-Battery Output. An open-drain N-channel MOSFET output. Sinks current when the voltage on LBI

drops below 1.25V. If unused, connect to GND.

14

LBI

Low-Battery Comparator Input. When the voltage on LBI drops below 1.25V, LBO sinks current. If unused,

connect to GND.

15

SHDN2 Active-Low Shutdown Input for DC-DC Controller 2. Connect to VDD for normal operation.

16

REF

Reference Bypass Input. Connect a 0.1µF ceramic capacitor from REF to GND.

_______________Detailed Description

The MAX863 dual, bi-CMOS, step-up, switch-mode

power-supply controller provides preset 3.3V, 5V, or

adjustable outputs. Its pulse-frequency-modulated

(PFM) control scheme combines the advantages of low

supply current at light loads and high efficiency with

heavy loads. These attributes make the MAX863 ideal

for use in portable battery-powered systems where

small size and low cost are extremely important, and

where low quiescent current and high efficiency are

needed to maximize operational battery life. Use of

external current-sense resistors and MOSFETs allows

the designer to tailor the output current and voltage

capability for a diverse range of applications.

PFM Control Scheme

Each DC-DC controller in the MAX863 uses a one-shot-

sequenced, current-limited PFM design, as shown in

Figure 1. Referring to the Typical Operating Circuit

(Figure 2) and the switching waveforms (Figures 3a–3f),

the circuit works as follows. Output voltage is sensed

by the error comparator using either an internal voltage

divider connected to SENSE1 or an external voltage

divider connected to FB1. When the output voltage

drops, the error comparator sets an internal flip-flop.

The flip-flop turns on an external MOSFET, which allows

inductor current to ramp-up, storing energy in a mag-

netic field.

_______________________________________________________________________________________ 5

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