UVLO

LM5026

1.25V

20 PA

Enable

R1

R2

0.4V

Standby

OFF

STANDBY

UVLO

LM5026

1.25V

20 PA

Enable Output

Drivers

R1

R2

0.4V

Regulators

PWR

1.25

R1

R2

V

1.25

´

=

-

HYS

V

R1

20 A

=

m

LM5026

www.ti.com

SNVS363E – AUGUST 2005 – REVISED NOVEMBER 2015

Application Information (continued)

8.1.3 Undervoltage Lockout (UVLO)

When the UVLO pin voltage is below 0.4 V, the controller is in a low current shutdown mode. When the UVLO

pin voltage is greater than 0.4 V but less than 1.25 V, the controller is in standby mode. When the UVLO pin

voltage is greater than 1.25 V, the controller is fully enabled. Typically, two external resistors program the

minimum operational voltage for the power converter as shown in Figure 26. When UVLO pin voltage is above

the 1.25-V threshold, an internal 20-

μA current source is enabled to raise the voltage at the UVLO pin, thus

providing threshold hysteresis. Resistance values for R1 and R2 can be determined from Equation 6 and

Equation 7:

where

•

(6)

.

where

•

(7)

30 V, R1 calculates to 150 k

Ω, and R2 calculates to 5.9 kΩ. The voltage at the UVLO pin should not exceed 6 V

at any time. Be sure to check both the power and voltage rating for the selected R1 resistor.

Remote configuration of the controller’s operational modes can be accomplished with open drain device(s)

connected to the UVLO pin as shown in Figure 27.

Figure 26. Basic UVLO Configuration

Figure 27. Remote Standby and Disable Control

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