Data Sheet

LT4423

analog.com

Rev. 0

13 of 18

Figure 18. Using an External MOSFET for Switching to High Current Loads

Reverse Input Voltage Protection

Some applications must tolerate momentary accidental reversed voltage connections or negative voltage transients

at the IN pin. Although the IN pin absolute maximum rating is limited to -0.3V, Figure 19 and Figure 20 demonstrate

how a resistor or simple diode may be added to permit reverse input voltage tolerance.

Under reverse input voltage, an internal substrate diode is turned on, and its current must be limited to below 100mA.

In Figure 19, a 100Ω 1/4-watt resistor (RGND) is added to the ground path, safely limiting internal power dissipation

under the reverse connection of the 4.2V battery.

Figure 19. Protecting Against Reverse Input Voltage with a Resistor

Placing the protection resistor in the ground path preserves the low IN to OUT power path resistance. Minor

drawbacks to using the protection resistor include a small increase in STATUS VOL and a minor shift in the SHDN

threshold, both dependent on the current in the STATUS pull-down path.

In the case of persistent reverse voltage, a simple diode (DGND) may be used in place of the ground resistor, as shown

in Figure 20. Using a diode removes power dissipation concerns at the expense of increased STATUS VOL, a shift in

SHDN

threshold, and an increase in minimum IN voltage by an amount equal to the diode drop voltage in the ground

path.

SiA469DJ

VIN1 = 4.2V

R2

51kΩ

COUT

100µF

C1

1µF

C2

1µF

R1

100kΩ

ROUT

4Ω

STATUS LOGIC

(0V TO 4V)

VOUT = 28V AT 7A OR 4V AT 1A

VIN2 = 28V

5.1V

BZT52H-B5V1

GND

IN

OUT

SHDN

STATUS

LT4423