Datasheet

EN
LM5001
V
PWR
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 PA
V
PWR
R2
LM5001 , LM5001-Q1
www.ti.com SNVS484G –JANUARY 2007–REVISED APRIL 2014
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 kΩ) 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
large resistance, R
SS
, preventing the SS circuit from interfering with the normal error amplifier function. During
shutdown, the VCC diode discharges the SS capacitor.
Copyright © 2007–2014, Texas Instruments Incorporated Submit Documentation Feedback 13
Product Folder Links: LM5001 LM5001-Q1