ZHCSI59I July 2009 – May 2018 TPS65070 , TPS65072 , TPS65073 , TPS650731 , TPS650732
UNLESS OTHERWISE NOTED, this document contains PRODUCTION DATA.
There are two resistors which set the default current for the current sinks at ISINK1 and ISINK2.
The resistor connected to ISET1 is used if Bit CURRENT LEVEL is set 1 in register 19h.
The resistor connected to ISET2 is used if Bit CURRENT LEVEL is set 0 in register 19h (default).
This allows switching between two different maximum values for the LED current with one Bit to extend the resolution for dimming.
Dimming is done by an internal PWM signal that turns on and off the current sinks ISINK1 and ISINK2 at 200Hz (default). The duty cycle range is 1% to 100% with a 1% resolution and a default duty cycle of 30%. In order to get the full scale LED current, the PWM dimming needs to be set to 100% in register 19h. This is done by writing 63h to register 19h.
KISET is defined to be 1000 in the electrical spec, the reference voltage at ISET1 and ISET2 is 1.24 V.
The current for each string is set by the resistor to:
A resistor value of 124 kΩ sets the current on each string to 10 mA.
For one string of wLEDs, both strings need to be connected in parallel, so the current in the wLEDs is twice the current programmed by the resistor at ISET1 or ISET2.
Connecting both strings in parallel is required because the wLED converter generates its output voltage dependant on the current in ISINK1 and ISINK2. If the current falls below the target, the output voltage is increased. If one string is open, the wLED driver will boost the output voltage to its maximum because it assumes the voltage is not high enough to drive current into this string (there could be different numbers of wLEDs in the two strings).