ZHCSI59I July 2009 – May 2018 TPS65070 , TPS65072 , TPS65073 , TPS650731 , TPS650732
UNLESS OTHERWISE NOTED, this document contains PRODUCTION DATA.
The white LED boost converter generates an output voltage, high enough to drive current through up to 10 white LEDs connected in series. TPS6507x support one or two strings of white LEDs. If two strings of white LEDs are used, the number of LEDs in each string is limited to 6LEDs due to the switch current limit as defined in the electrical characteristics. The boost converter block contains two current sinks to control the current through the white LEDs. The anodes of the “upper” white-LEDs are directly connected to the output voltage at the output capacitor. The cathode of the “lowest” LED is connected to the input of the current sink at pin ISINK1 or ISINK2. The internal current sink controls the output voltage of the boost converter such that there is a minimum voltage at the current sink to regulate the defined current. The maximum current is set with a resistor connected from pin ISET1 to GND. Dimming is done with an internal PWM modulator by changing the duty cycle in the current sinks from 1% to 100%. In order to set a LED current of less than 1% of the current defined at ISET1, a second current range is set with a resistor at pin ISET2 to GND. By changing between the two current ranges and varying the duty cycle, it is possible to achieve a dimming ratio of > 1:100. The main functions of the converter like enable / disable of the converter, PWM duty cycle and dimming frequency are programmed in registers WLED_CTRL1 and WLED_CTRL2 – see the register description for details.
If only one string of white LEDs are used, ISINK1 and ISINK2 need to be connected in parallel.