VIN

EN

PWMx

FAULT

REF

Switching

VOUT

IFBx

UVLO

Rising Threshold

REF Voltage = OVP Voltage

Unused Channel

Detection

Falling Threshold

VDD

20ms

200 s

μ

40 s

μ

TPS61196

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SLVSBG1C – OCTOBER 2012 – REVISED FEBRUARY 2013

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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