EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: tlwEEVblog on March 26, 2022, 01:57:59 am
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Has anyone observed a power-up issue with the al8843 chip? We designed and are testing our own PCB design using the al8843 chip. The design is based on a modified version of the circuit recommended in the datasheet. We added a trim pot to the current sense resistor to allow us to easily adjust the current set point. We are NOT using the PWM control. We are using a lab power supply as the source. The circuit seems to be regulating as expected over a wide input voltage range and current set points. However we have observed that at under some current set points and supply voltages, when the power supply is turned on, the chip does not start correctly and the internal switch transistor is stuck in the ON condition (no switching). If we test the same circuit by disconnecting and re-connecting the cable from the supply, then it works properly. It seems that the rise-time of the power supply turning on is the issue. Like the chip wants to see a fast rise time on the supply input. I am considering using the CTRL pin to solve the issue, but haven't tried it yet. By putting a resistor- capacitor at the control pin to hold the switch OFF until the power supply has stabilized, much like a reset circuit on a microprocessor chip.