11

LM2594, LM2594HV

www.ti.com

SNVS118D – DECEMBER 1999 – REVISED MAY 2016

Product Folder Links: LM2594 LM2594HV

Submit Documentation Feedback

Copyright © 1999–2016, Texas Instruments Incorporated

Feature Description (continued)

Figure 14. Delayed Start-Up

8.3.2 Undervoltage Lockout

Some applications require the regulator to remain off until the input voltage reaches a predetermined voltage.

Figure 15 shows an undervoltage lockout feature applied to a buck regulator, while Figure 16 and Figure 17

apply the same feature to an inverting circuit. The circuit in Figure 16 features a constant threshold voltage for

turnon and turnoff (Zener voltage plus approximately 1 V). If hysteresis is needed, the circuit in Figure 17 has a

turnon voltage which is different than the turnoff voltage. The amount of hysteresis is approximately equal to the

value of the output voltage. If Zener voltages greater than 25 V are used, an additional 47-kΩ resistor is needed

from the ON/OFF pin to the ground pin to stay within the 25 V maximum limit of the ON/OFF pin.

Figure 15. Undervoltage Lockout

for Buck Regulator

8.3.3 Inverting Regulator

The circuit in Figure 18 converts a positive input voltage to a negative output voltage with a common ground. The

circuit operates by bootstrapping the regulators ground pin to the negative output voltage, then grounding the

feedback pin, the regulator senses the inverted output voltage and regulates it.

This circuit has an ON/OFF threshold of approximately 13 V.

Figure 16. Undervoltage Lockout for Inverting Regulator