(

)

( )

( )

(

)

SS

ref

SS

SS

C

nF

V

V

T

ms

=

I

A

´

m

EN

START

EN

V

Ren2 =

V

- V

+ 1

A

Ren1

m

START

STOP

V

- V

Ren1 =

3

A

m

EN

1.25V

VIN

+

-

Ren1

Ren2

TPS54331

1

A

m

3

A

m

TPS54331

www.ti.com

SLVS839F – JULY 2008 – REVISED OCTOBER 2014

Feature Description (continued)

The TPS54331 device is disabled when the VIN pin voltage falls below the internal VIN UVLO threshold. Using

adjust the VIN UVLO with hysteresis, use the external circuitry connected to the EN pin as shown in Figure 9.

When the EN pin voltage exceeds 1.25 V, an additional 3

μA of hysteresis is added. Use Equation 1 and

threshold should always be greater than 3.5 V.

Figure 9. Adjustable Input Undervoltage Lockout

where

•

•

(1)

where

•

(2)

8.3.5 Programmable Slow Start Using SS Pin

Programming the slow-start time externally is highly recommended because no slow-start time is implemented

internally. The TPS54331 device effectively uses the lower voltage of the internal voltage reference or the SS pin

voltage as the reference voltage of the power supply that is fed into the error amplifier and regulates the output

an internal pullup current-source of 2

μA that charges the external slow-start capacitor. Use Equation 3 to

calculate the slow-start time (10% to 90%).

where

•

•

(3)

The slow-start time should be set between 1 ms to 10 ms to ensure good startup behavior. The value of the

slow-start capacitor should not exceed 27 nF.

During normal operation, the TPS54331 device stops switching if the input voltage drops below the VIN UVLO

threshold, the EN pin is pulled below 1.25 V, or a thermal shutdown event occurs.

Copyright © 2008–2014, Texas Instruments Incorporated

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