MAX4193CSLASHD datasheet(5/14 Pages) MAXIM

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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

The shutdown mode is entered whenever IC (pin 6) is

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

MAX630’s analog circuitry, oscillator, LX, and LBD out-

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

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

Bootstrapped Operation

In most circuits, the preferred source of +VS voltage for

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.

The on-resistance of the N-channel LX output decreas-

es with an increase in +VS; however, the device operat-

ing current goes up with +VS (see the Typical

Operating Characteristics, IS vs. +VS graph). In circuits

with very low output current and input voltages greater

than 3V, it may be more efficient to connect +VS direct-

ly to the input voltage rather than bootstrap.

CMOS Micropower Step-Up

Switching Regulator

_______________________________________________________________________________________

COMP 2

+5V INPUT

169k

100k

470

LOW BATTERY INPUT

1.31V

OSC

RON

≅ 3Ω

40kHz

COMP 1

1.31V

BANDGAP

REFERENCE

AND

BIAS GENERATOR

1 LBR

2CX

3LX

4 GND

1N4148

+VS 5

IC 6

VFB 7

LBD 8

LOW-BATTERY OUTPUT

(LOW IF INPUT < 3V)

499k

47.5k

SHUTDOWN

OPERATE

+15V OUTPUT

20mA

470

μF

25V

MAX630

COMP 2

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

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