Datasheet

CTRL
low
high
FB
200mVxdutycycle
Insertbattery
CTRL
low
high
FB
Insertbattery
Programming
code
FBramp
Shutdowndelay
t
EnterESmode
Timingwindow
Programmingcode
50mV 50mV
EnterESmode
PWMsignal
Startup
delay
PWM
mode
Startupdelay
FBramp
Programmedvalue
(ifnotprogrammed, 200mVdefault)
Shutdown
delay
IC
Shutdown
Startupdelay
FBramp
ES
mode
ESdetectdelay
ESdetecttime
V
FB
+ Duty 200 mV
TPS61160
TPS61161
www.ti.com SLVS791C –NOVEMBER 2007–REVISED APRIL 2012
LED BRIGHTNESS DIMMING MODE SELECTION
The CTRL pin is used for the control input for both dimming modes, PWM dimming and 1 wire dimming. The
dimming mode for the TPS61160/1 is selected each time the device is enabled. The default dimming mode is
PWM dimming. To enter the 1 wire mode, the following digital pattern on the CTRL pin must be recognized by
the IC every time the IC starts from the shutdown mode.
1. Pull CTRL pin high to enable the TPS61160/1, and to start the 1 wire detection window.
2. After the EasyScale detection delay (t
es_delay
, 100μs) expires, drive CTRL low for more than the EasyScale
detection time (t
es_detect
, 260μs).
3. The CTRL pin has to be low for more than EasyScale detection time before the EasyScale detection window
(t
es_win
, 1msec) expires. EasyScale detection window starts from the first CTRL pin low to high transition.
The IC immediately enters the 1 wire mode once the above 3 conditions are met. the EasyScale communication
can start before the detection window expires. Once the dimming mode is programmed, it can not be changed
without another start up. This means the IC needs to be shutdown by pulling the CTRL low for 2.5ms and
restarts. See the Dimming Mode Detection and Soft Start (Figure 13) for a graphical explanation.
Figure 13. Dimming Mode Detection and Soft Start PWM Brightness Dimming
PWM BRIGHTNESS DIMMING
When the CTRL pin is constantly high, the FB voltage is regulated to 200mV typically. However, the CTRL pin
allows a PWM signal to reduce this regulation voltage; therefore, it achieves LED brightness dimming. The
relationship between the duty cycle and FB voltage is given by Equation 2.
(2)
Where
Duty = duty cycle of the PWM signal
200 mV = internal reference voltage
As shown in Figure 14, the IC chops up the internal 200mV reference voltage at the duty cycle of the PWM
signal. The pulse signal is then filtered by an internal low pass filter. The output of the filter is connected to the
error amplifier as the reference voltage for the FB pin regulation. Therefore, although a PWM signal is used for
brightness dimming, only the WLED DC current is modulated, which is often referred as analog dimming. This
eliminates the audible noise which often occurs when the LED current is pulsed in replica of the frequency and
duty cycle of PWM control. Unlike other scheme which filters the PWM signal for analog dimming, TPS61160/1
regulation voltage is independent of the PWM logic voltage level which often has large variations.
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Product Folder Link(s): TPS61160 TPS61161