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LM43602-Q1

SNVSA83C – APRIL 2015 – REVISED OCTOBER 2017

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Copyright © 2015–2017, Texas Instruments Incorporated

8.2.2.11 Soft-Start Capacitors

The user can left the SS/TRK pin floating, and the LM43602-Q1 will implement a soft-start time of 4.1 ms

typically. In order to use an external soft start capacitor, the capacitor must be sized so that the soft-start time is

longer than 4.1 ms. Use Equation 23 in order to calculate the soft start capacitor value:

where

•

CSS = Soft start capacitor value (µF)

•

ISS = Soft start charging current (µA)

•

tSS = Desired soft start time (s)

(23)

For the desired soft start time of 10 ms and soft start charging current of 2 µA, Equation 23 above yield a soft

start capacitor value of 0.02 µF.

8.2.2.12 Undervoltage Lockout Setpoint

The undervoltage lockout (UVLO) is adjusted using the external voltage divider network of RENT and RENB. RENT

is connected between VIN and the EN pin of the LM43602-Q1 device. RENB is connected between the EN pin

and the GND pin. The UVLO has two thresholds, one for power up when the input voltage is rising and one for

power down or brown outs when the input voltage is falling. Equation 24 can be used to determine the VIN

(UVLO) level.

VIN-UVLO-RISING = VENH × (RENB + RENT) / RENB

(24)

The EN rising threshold (VENH) for LM43602 is set to be 2.2 V (typical). Choose the value of RENB to be 1 MΩ to

minimize input current from the supply. If the desired VIN UVLO level is at 5 V, the value of RENT can be

calculated using Equation 25:

RENT = (VIN-UVLO-RISING / VENH -1) × RENB

(25)

Equation 25 yields a value of 1.27 MΩ. The resulting falling UVLO threshold, equals 4.3 V, can be calculated by

Equation 26, where EN falling threshold (VENL) is 1.9 V (typical).

VIN-UVLO-FALLING = VENL × (RENB + RENT) / RENB

(26)

8.2.2.13 PGOOD

A typical pullup resistor value is 10 k

Ω to 100 kΩ from PGOOD pin to a voltage no higher than 12 V. If it is

desired to pull up PGOOD pin to a voltage higher than 12 V, a resistor can be added from PGOOD pin to ground

to divide the voltage seen by the PGOOD pin to a value no higher than 12 V.