LTC2953

18

2953f

TYPICAL APPLICATIONS

Dual Supply Monitor with μP Reset

The circuit of Figure 22 monitors two supplies and provides

a μP reset. When either the

⎯P⎯F⎯I or the VM input voltage

falls below its threshold (0.5V), the

⎯R⎯S⎯T output is asserted

low.

⎯R⎯S⎯T remains low for 200ms after both inputs rise

above 0.5V. The low leakage

⎯P⎯F⎯O output allows for large

valued external resistors.

Reverse Battery Protection

To protect the LTC2953 from a reverse battery connec-

See Figure 23.

2953 F22

LTC2953

–

+

–

+

0.5V

0.5V

RST

RST

PFI

VM

PFO

μP

V2

V1

ON/OFF

EN

LTC2953-1

LT1761

SHDN

8.4V

R5

910k

2953 F23

PB

+

R8

1k

Figure 22. Dual Supply Monitor with μP Reset

Figure 23. Reverse Battery Protection Using R8

Operation with Supply Transients over 40V

The application circuit of Figure 24 operates from a 24V

nominal supply, but can withstand supply transients as

high as 40V.

The high voltage

⎯E⎯N output of the LTC2953-2 has an ab-

solute maximum rating of 50V, which makes it suitable for

driving the gate of the external power PFET. The external

30V Zener diode (Z1) and the 10k current limiting resistor

that under normal 24V operation, the external Zener diode

does not conduct any current. The voltage drop across

RZ should be kept below 1V. Z2 should have a breakdown

voltage smaller than the PFET’s gate-to-source breakdown

voltage.

ON/OFF

EN

LTC2953-2

2953 F24

PB

R5

100k

RZ

10k

R9

100k

24V NOMINAL,

40V TRANSIENTS

FDS4685

Si2319DS

NDS9407

10V

Z2

BZX84C10

30V

Z1

BZX84C30

50V

ABS MAX

1

μF

50V

Figure 24. Operation with 40V Supply Transients

Power Path Controller with Low Battery Detect

The application in Figure 25 uses the push button to

completely disconnect the load from the battery. If the

battery voltage falls below the user specified threshold, the

push button is prevented from turning on system power

(asserting the enable output).