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possible TEC current spike on startup #56

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opened 2021-02-10 15:03:48 +08:00 by sb10q · 1 comment
sb10q commented 2021-02-10 15:03:48 +08:00
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The AD5680 DAC outputs either 0V or 2.5V (depending on the exact DAC model) when powered up, and until the firmware reprograms it.
With the 0V version which is assembled on some boards (marked "D3C"), it would create a significant current spike during startup.
Check that:

  • the STM32 drives the SHDN# pin low until the firmware starts. If that is not the case, the hardware may need an additional pull-down resistor. it doesn't, pin defaults to input mode and is floating. Pull down is required.
  • The firmware programs the DAC with a sensible value, and sets TEC current limits, before deasserting SHDN#.
The AD5680 DAC outputs either 0V or 2.5V (depending on the exact DAC model) when powered up, and until the firmware reprograms it. With the 0V version which is assembled on some boards (marked "D3C"), it would create a significant current spike during startup. Check that: * <s>the STM32 drives the SHDN# pin low until the firmware starts. If that is not the case, the hardware may need an additional pull-down resistor.</s> it doesn't, pin defaults to input mode and is floating. Pull down is required. * The firmware programs the DAC with a sensible value, and sets TEC current limits, before deasserting SHDN#.
topquark12 was assigned by sb10q 2021-02-10 15:03:48 +08:00
topquark12 commented 2021-02-11 10:59:07 +08:00

Currently the firmware drives the shutdown pin low when initializing GPIO, and only drives it high after limits and dac has been set.

Though the state of the pin is still unknown between power on to code excecution, or when the MCU is in reset, DFU etc. A hardware pull down should be added.

Currently the firmware drives the shutdown pin low when initializing GPIO, and only drives it high after limits and dac has been set. Though the state of the pin is still unknown between power on to code excecution, or when the MCU is in reset, DFU etc. A hardware pull down should be added.
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Reference: M-Labs/thermostat#56
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