Datasheet

V
1V/div,18Voffset
O
InductorCurrent
100mA/div
t- Time=4ms/div
V
5V/div
O
LEDCurrent
50mA/div
InductorCurrent
200mA/div
t- Time=2ms/div
V
5V/div
O
LEDCurrent
50mA/div
InductorCurrent
200mA/div
t- Time=400 s/divm
DETAILED DESCRIPTION
OPERATION
TPS61166
SLVS991 – SEPTEMBER 2009 .......................................................................................................................................................................................... www.ti.com
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 Submit Documentation Feedback Copyright © 2009, Texas Instruments Incorporated
Product Folder Link(s): TPS61166