EN

LM5001

STANDBY

R2

OFF

OFF

STANDBY

R1

1.26V

0.45V

EN

LM5001

Disable PWM Controller

R1

Disable VCC Regulator

VIN

1.26V

0.45V

6 2A

R2

LM5001, LM5001-Q1

www.ti.com

SNVS484H – JANUARY 2007 – REVISED JULY 2015

Application Information (continued)

Figure 15. Basic EN (UVLO) Configuration

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

connected to the EN pin as shown in Figure 16. A MOSFET or an NPN transistor connected to the EN pin can

force the regulator into the low power ‘off’ state. Adding a PN diode in the drain (or collector) provides the offset

to achieve the standby state. The advantage of standby is that the VCC LDO is not disabled and external

circuitry powered by VCC remains functional.

Figure 16. Remote Standby and Disable Control

8.1.4 Soft-Start

Soft-start (SS) can be implemented with an external capacitor connected to COMP through a diode as shown in

Figure 17. The COMP discharge MOSFET conducts during Shutdown and Standby modes to keep the COMP

voltage below the PWM offset (1.3 V), which inhibits PWM pulses. The error amplifier attempts to raise the

COMP voltage after the EN pin exceeds the 1.26-V standby threshold. Because the error amplifier output can

only sink current, the internal COMP pull-up resistor (~5 k

Ω) supplies the charging current to the SS capacitor.

The SS capacitor causes the COMP voltage to gradually increase, until the output voltage achieves regulation

and FB assumes control of the COMP and the PWM duty cycle. The SS capacitor continues charging through a

shutdown, the VCC diode discharges the SS capacitor.

Copyright © 2007–2015, Texas Instruments Incorporated

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