V

1V/div,18Voffset

O

InductorCurrent

100mA/div

t- Time=4ms/div

V

5V/div

O

LEDCurrent

50mA/div

InductorCurrent

200mA/div

t- Time=2ms/div

V

5V/div

O

LEDCurrent

50mA/div

InductorCurrent

200mA/div

t- Time=400

s/div

m

DETAILED DESCRIPTION

OPERATION

TPS61166

OVER VOLTAGE PROTECTION

SOFT START UP IN PWM DIMMING

Figure 15.

Figure 16.

SOFT START UP

Figure 17.

The TPS61166 adopts peak current-mode control with a constant pulse-width-modulation (PWM) frequency of

1.2-MHz. PWM operation turns on the PWM switch at the beginning of each switching cycle. The input voltage is

applied across the inductor and the inductor current ramps up. In this mode, the output capacitor is discharged

by the load current. When the inductor current hits the threshold set by the error amplifier output, the PWM

switch is turned off, and the power diode is forward-biased. The inductor transfers its stored energy to replenish

the output capacitor. This operation repeats in the next switching cycle. The error amplifier compares the FB pin

voltage with an internal reference, and its output determines the duty cycle of the PWM switching. This

closed-loop system requires frequency compensation for stable operation. The device has a built-in

compensation circuit that can accommodate a wide range of input and output voltages. To avoid the

sub-harmonic oscillation intrinsic to current-mode control, the IC also integrates the slope compensation, which

adds an artificial slope to the current ramp.

10

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