Low-Battery Detector

The low-battery detector compares the voltage on LBR

with the internal 1.31V reference. The output, LBD, is an

open-drain N-channel MOSFET. In addition to detecting

and warning of a low battery voltage, the comparator

can also perform other voltage-monitoring operations

such as power-failure detection.

Another use of the low-battery detector is to lower the

oscillator frequency when the input voltage goes below

a specified level. Lowering the oscillator frequency

increases the available output power, compensating for

the decrease in available power caused by reduced

input voltage (see Figure 5).

Logic-Level Shutdown Input

driven below 0.2V or left floating. When shut down, the

puts are turned off. The device’s quiescent current dur-

ing shutdown is typically 10nA (1µA max).

Bootstrapped Operation

the MAX630 and MAX4193 is the boosted output volt-

age. This is often referred to as a “bootstrapped” oper-

ation since the circuit figuratively “lifts” itself up.

with very low output current and input voltages greater

ly to the input voltage rather than bootstrap.

CMOS Micropower Step-Up

Switching Regulator

_______________________________________________________________________________________

5

COMP 2

+5V INPUT

R3

169k

Ω

R4

100k

Ω

L1

470

LOW BATTERY INPUT

1.31V

OSC

≅ 3Ω

40kHz

COMP 1

1.31V

BANDGAP

REFERENCE

AND

BIAS GENERATOR

1 LBR

4 GND

D1

1N4148

LBD 8

LOW-BATTERY OUTPUT

(LOW IF INPUT < 3V)

R1

499k

Ω

R2

47.5k

Ω

SHUTDOWN

OPERATE

+15V OUTPUT

20mA

C1

470

μF

25V

MAX630

COMP 2

Figure 1. +5V to +15V Converter and Block Diagram