EN

ip

ih

VIN

TPS54821

R 1

R 2

EN

ip

ih

PVIN

TPS54821

R 1

R 2

EN

ip

ih

VIN

TPS54821

R 1

R 2

1

æ

ö

-

ç

÷

è

ø

æ

ö

-

+

ç

÷

è

ø

ENFALLING

START

STOP

ENRISING

ENFALLING

p

h

ENRISING

V

V

V

V

R1 =

V

I

I

V

(

)

´

-

+

+

ENFALLING

STOP

ENFALLING

p

h

R1 V

R2 =

V

V

R1 I

I

TPS54821

SLVSB14

– OCTOBER 2011

www.ti.com

If an application requires either a higher UVLO threshold on the VIN pin or a secondary UVLO on the PVIN, in

split rail applications, then the EN pin can be configured as shown in Figure 17, Figure 18 and Figure 19. When

using the external UVLO function it is recommended to set the hysteresis to be greater than 500mV.

The EN pin has a small pull-up current Ip which sets the default state of the pin to enable when no external

components are connected. The pull-up current is also used to control the voltage hysteresis for the UVLO

calculated using Equation 2 and Equation 3.

Figure 17. Adjustable VIN Undervoltage Lock Out

Figure 18. Adjustable PVIN Undervoltage Lock Out, VIN

≥ 4.5V

Figure 19. Adjustable VIN and PVIN Undervoltage Lock Out

(2)

(3)

12

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