(

)

( )

( )

(

)

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

1.25 V

VIN

+

–

Ren1

Ren2

TPS54531

1

A

m

3

A

m

TPS54531

SLVSBI5A – MAY 2013 – REVISED OCTOBER 2014

www.ti.com

Feature Description (continued)

The TPS54531 device is disabled when the VIN pin voltage falls below the internal VIN UVLO threshold. Using

an external VIN UVLO to add at least 500-mV hysteresis is recommended unless the VIN voltage is greater than

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 Equation 2 to calculate the resistor values required for the desired VIN UVLO threshold voltages.

Figure 9. Adjustable Input Undervoltage Lockout

where

•

•

(1)

where

•

(2)

The external start and stop voltages are approximate. The actual start and stop voltages may vary.

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 TPS54531 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 slow-start

capacitor should not exceed 27 nF.

During normal operation, the TPS54531 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.

10

Submit Documentation Feedback

Copyright © 2013–2014, Texas Instruments Incorporated

Product Folder Links: TPS54531