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TPS61177A Usage and Programming
6
TPS61177A Usage and Programming
The TPS61177A white LED driver can be programmed to support optimal application configuration for
boost and LED driver control by register control. The boost converter can operate at 4 switching
frequencies. Options can be set for slew rate control. The dimming can be done with a full PWM output,
linear current control, or an adaptive combination of the two for the both power savings and good dimming
quality. Shutdown for current limit can be also set to protect the circuit.
6.1
In-Circuit Operation
The TPS61177A white LED driver can be controlled during operation with I2C register accesses and PWM
input signal. I2C register access can be used for boost and LED driver control, and PWM input can be
used to adjust output dimming level of LED driver. Default EEPROM settings can be loaded to internal
registers at power up and these registers can be programmed for application conditions and burned in
EEPROM by simple I2C sequence.
6.2
ENABLE
The EN pin controls enabling and shutdown of the TPS61177A. A zero value on this pin holds the device
in shutdown with minimum current consumption. Register access is not available during shutdown. Boost
will not switch until valid PWM input higher than 0% is applied.
6.3
Boost Converter Configuration
The TPS61177A boost converter configuration is determined by the size of the LED array to be driven.
Additionally, component constraints will affect operating frequency selection. A calculation method is
described in datasheet for selecting the boost operating point and external components along with the
desired frequency of operation.
6.3.1
Setting the Boost Switching Frequency
The desired frequency of operation is programmed in the FREQ bits of the A3h register. The default value
of FREQ bits is 01b setting 600kHz.
6.3.2
Setting the Boost Voltage
The boost voltage can be adaptively set by the TPS61177A to control the LED headroom in real time
which provides the most efficient operation. Boost maximum voltage is 39 V which can support up to 11 to
13 LEDs.
6.3.3
Setting the Boost Switch Slew Rate
The boost switch slew rate can be programmed in the SR bits of the A4h register. The slew rate control
can be used for optimization of EMI caused by boost or system efficiency
6.4
LED Driver Configuration
The LED driver can control the power to the LEDs using PWM dimming, pure current control, or an
adaptive combination of the two. See the Adaptive Dimming Control and Brightness Control sections of
the data sheet for descriptions.
6.4.1
Setting the Maximum LED Current
The desired maximum LED current is set in the CS bits of A1h. The CS value in A1h can be used for finer
adjustments of the maximum current. The default value of CS bits is 101b setting 20 mA.
6.4.2
PWM Output Frequency
PWM output freq on direct PWM mode and mixed dimming mode is determined by input PWM frequency.
24
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Copyright © 2015, Texas Instruments Incorporated
www.ti.com
SNVU490 – OCTOBER 2015
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