TPS61196
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SLVSBG1C –OCTOBER 2012–REVISED FEBRUARY 2013
VIN
Rising Threshold
Falling Threshold
UVLO
EN
40μs
VDD
PWMx
FAULT
REF
REF Voltage = OVP Voltage
VOUT
Switching
IFBx
Unused Channel
Detection
200μs
20ms
Figure 23. Power up Sequencing
The TPS61196 has integrated the soft-start circuitry working with an external capacitor at the REF pin to avoid
inrush current during startup. During the startup period, the capacitor at the REF pin is charged with a soft-start
current source. When the REF pin voltage is higher than the output feedback voltage at the OVP pin, the boost
controller starts switching and the output voltage starts to ramp up. At the same time, the LED current sink starts
to drive the LED strings. At the beginning of the soft start, the charge current is 200µA. Once the voltage of the
REF pin exceeds 2.0V, the charge current changes to 10µA and continues to charge the capacitor. When the
current sinks are driving the LED strings, the IFB voltages are monitored. When the minimum IFB voltage is
above 200mV less than the setting voltage at the IFBV pin, the charge current is stopped and the soft startup is
finished. The TPS61196 enters normal operation to regulate the minimum IFB voltage to the required voltage set
by the resistor at the IFBV pin. The total soft start time is determined by the external capacitance. The
capacitance must be within 1.0µF to 4.7µF for different startup time and different output voltage.
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