Datasheet

COMP
SS
SOFT-START
CAPACITOR
LM5015
C
SS
11 PA
ENABLE
VDD
PWM
CURRENT
LIMIT
1.5V
1.3V
VDD (5V)
1.26V
5k
FB
V
OUT
EN
LM5015
V
PWR
1.26V
STANDBY
R1
R2
0.45V
SHUTDOWN
OFF
STANDBY
LM5015
www.ti.com SNVS538C –NOVEMBER 2007–REVISED APRIL 2013
Figure 19. Remote Standby and Disable Control
SOFT-START
Soft-start is implemented with an external capacitor C
SS
connected to the SS pin as shown in Figure 20. The SS
discharge MOSFET conducts during Shutdown and Standby modes. When the SS pin is low, the COMP voltage
is held below the PWM offset voltage (1.3V) by the SS buffer amplifier, thus inhibiting PWM pulses. When the EN
pin exceeds the 1.26V standby threshold, the ENABLE signal will turn-off the SS discharge MOSFET and allow
the internal 11 µA current source to charge the SS capacitor. The COMP voltage will follow the SS voltage under
the control of the open-drain SS buffer amplifier. The C
SS
capacitor will cause the COMP voltage to gradually
increase, until the output voltage achieves regulation, and the error amplifier assumes control of the COMP and
the PWM duty cycle. The C
SS
capacitor continues charging by the internal 11 µA current source, preventing the
SS voltage from interfering with the normal error amplifier function. During shutdown, the SS discharge MOSFET
conducts to discharge the C
SS
capacitor.
Figure 20. Soft-Start
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