Hello,
We are using TPS61042 for the LED brightness control.
We connect 2 LEDs in series at output of LED Driver (Pin-7 OVP and Pin-1 LED).
Circuit diagram is as given below figure.
At resistor Rs = 4.8 ohm, we get drop across that resistor Vfb = 0.252V (252mV).
LED1 forward voltage = 1.234V and LED2 forward voltage = 1.509V.
But, as we change input between 4V to 5.5V, 252mV does not remain constant in given input range.
So, as 252mV changes as per equation given in datasheet LED current varies. Hence, LED current doesn’t remain constant.
Please give suggestion for how to make current constant and feedback voltage VFB = 252mV.
For proper constant current circuit operation, is there any requirement that output must be greater than input? (boost operation).
And in datasheet of TPS61042 it is said that maximum LED switch current ILED = 60mA and MOSFET current limit ILIM = 500mA (typ.).
So, in what circuit configuration we can get LED current up to 60mA with constant LED current and VFB = 252mV?.
Thanks.
