Datasheet

10
0.2
0
2015 25 30 4035
0.4
1.0
0.8
1.2
0.6
V
UVLO
– Undervoltage Lockout Threshold – V
V
UVLO
– Hysteresis – V
UDG-02132
Clock
PWM RAMP
PowerGood
VIN
UVLO Threshold
1 2 3 4 5 6 7 1 2 3 4 5 6 71 2
TPS40054
TPS40055
TPS40057
www.ti.com SLUS593H –DECEMBER 2003–REVISED JULY 2012
Figure 4. Undervoltage Lockout Operation
The tolerance on the UVLO set point also affects the maximum duty cycle achievable. If the UVLO starts the
device at 10% below the nominal start-up voltage, the maximum duty cycle is reduced approximately 10% at the
nominal start-up voltage.
The impedance of the input voltage can cause the input voltage, at the controller, to sag when the converter
starts to operate and draw current from the input source. Therefore, there is voltage hysteresis that prevents
nuisance shutdowns at the UVLO point. With R
T
chosen to select the operating frequency and R
KFF
chosen to
select the start-up voltage, the approximate amount of hysteresis voltage is shown in Figure 5.
UNDERVOLTAGE LOCKOUT THRESHOLD
vs
HSYTERESIS
Figure 5.
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