17W LED Driver (TPS92691)¶
Description¶
A Ø 70mm circular-shaped daughter PCBA for product status indication and receiving IR signal from remote control. Indicators are driven by NPN transistors. MCU roles includes controlling indication LEDs, driving piezoelectric buzzer with 4kHz PWM, decoding NEC IR signals, USART communication with main controller, and controlling LED brightness.
The LED driver is based on TI TPS92691 in boost topology with 24V input and ~45V output. Information on the LED panel can be found here. Through testing, using analog dimming alone was able to achieve 100:1 dimming ratio. An automatic calibration step was added in production line to correct the output current levels due to the variation of amplifier input offset. The driver IC boasts 1000:1 dimming ratio using PWM dimming hence both hardware and firmware were developed to support it initially, but removed eventually once analog dimming alone was validated to be able to achieve the design target of 100:1 dimming ratio.
Connection¶
Connection to the main controller was done using spring contacts. Contact is made when the plastic cover holding the PCBA is fastened onto a contact board on main body of appliance. The supply and ground contact pads on the contact board were designed to be longer so that they make contact before the communication lines.
Mated view:
Block Diagram¶
Gallery¶
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