ZHCSI59I July 2009 – May 2018 TPS65070 , TPS65072 , TPS65073 , TPS650731 , TPS650732
UNLESS OTHERWISE NOTED, this document contains PRODUCTION DATA.
The converter is in shutdown mode by default and is being turned on by setting the enable Bit with the I2C interface or for TPS65072 with pin EN_wLED. The enable Bit is located in register WLED_CTRL1 and is called ENABLE ISINK as it enables the current sink for the white LEDs. Once enabled, an output voltage is automatically generated at FB_wLED, high enough to force the programmed current through the string of white LEDs. Two strings of white LEDs can be powered. The current in each of the two strings is regulated by an internal current sink at pins Isink1 and Isink2. The maximum current through the current sinks is set with two external resistors connected from pins ISET1 and ISET2 to GND. ISET1 sets the maximum current when Bit CURRENT LEVEL in register WLED_CTRL2 is set to 1. If this Bit is set to 0, which is the default setting, the maximum current is defined by the resistor connected at ISET2. This allows change between two different maximum current settings during operation. The LED current can further be dimmed with an internal PWM signal. The duty cycle for this PWM signal can be changed with the Bits LED DUTY CYCLE 0 to LED DUTY CYCLE 6 in register WLED_CTRL2 in a range from 1% to 100%. In case a dimming ratio higher than 1:100 is needed, the maximum LED current need to be changed to a lower value as defined with Iset2. In order to do this without any flicker, the PWM dimming and the current level is defined in the same register, so both settings can be changed at the same time with a single write access to register WLED_CTRL2. An internal overvoltage protection limits the maximum voltage at FB_wLED to 37 V typically. The output voltage at FB_WLED also has a lower limit which is set to 12 V. In case less than 4LEDs are used, the output voltage at the boost converter will not drop below 12 V but the voltage from ISINK1 and ISINK2 to GND is increased accordingly.