1- to 3-Cell, High-Current, Low-Noise,

Step-Up DC-DC Converters with Linear Regulator

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9

______________________________________________________________Pin Description

Boost DC-DC Converter Power Output. POUT is the source of the P-channel synchronous-rectifier MOSFET

switch. Connect an external Schottky diode from LX to POUT. The output current available from POUT is

reduced by the current drawn from the LDO linear-regulator output.

POUT

16

On Control Input. When ONA = high or ONB = low, the IC turns on. Connect ONA to OUT for normal

operation (Table 2).

ONA

15

Off Control Input. When ONB = high and ONA = low, the IC is off. Connect ONB to GND for normal

operation (Table 2).

ONB

14

Inductor connection to the drains of the P-channel synchronous rectifier and N-channel switch

LX

13

Power Ground for the source of the N-channel power MOSFET switch

PGND

12

Low-Dropout Linear-Regulator Output. LDO sources up to 200mA. Bypass to GND with a 22µF capacitor.

LDO

9

Low-Battery Comparator Output. This open-drain, N-channel output is low when LBP < LBN.

Input hysteresis is 16mV.

LBO

10

Switching-Mode Selection and External-Clock Synchronization Input:

• CLK/SEL = low: low-power, low-quiescent-current PFM mode.

• CLK/SEL = high: low-noise, high-power PWM mode. Switches at a constant frequency (300kHz). Full

output power is available.

• CLK/SEL = driven with an external clock: low-noise, high-power synchronized PWM mode.

Synchronizes to an external clock (from 200kHz to 400kHz).

Turning on the DC-DC converter with CLK/SEL = GND also serves as a soft-start function,

since peak inductor current is reduced.

CLK/SEL

11

Ground

GND

5

Step-Up Converter Feedback Input, used during track mode. IC power and low-dropout linear-regulator

input. Bypass OUT to GND with a 0.1µF ceramic capacitor placed as close to the IC as possible.

OUT

6

Step-Up DC-DC Converter Feedback Input. Connect FB to a resistor voltage divider between POUT and

GND to set the output voltage between 2.5V and 5.5V. FB regulates to 1.233V.

FB

7

Low-Dropout Linear-Regulator Feedback Input. Connect FBLDO to a resistor voltage divider between LDO

FBLDO

8

Track-Mode Control Input for DC-DC Converter. In track mode, the boost-converter output is sensed at

OUT and set 0.3V above LDO to improve efficiency. Set TRACK to OUT for track mode. Connect TRACK to

GND for normal operation.

TRACK

4

1.250V Reference Output. Bypass REF with a 0.33µF capacitor to GND. REF can source up to 50µA.

REF

3

PIN

Low-Battery Comparator Inverting Input. Common-mode range is 0.5V to 1.5V.

LBN

2

Low-Battery Comparator Noninverting Input. Common-mode range is 0.5V to 1.5V.

LBP

1

FUNCTION

NAME