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3V3A is unstable if PD Mon Output Stage Voltage is larger than 3.3V #47

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opened 2024-07-19 10:48:56 +08:00 by linuswck · 0 comments
linuswck commented 2024-07-19 10:48:56 +08:00
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Test environment

Hardware Revision: rev0_3
Power: Via 12V Power Jack
PD Mon Current Range is custom made to be 0 - 187uA.
Laser Diode used: BFLD-974f-4HSM-NO
PID is autotune-ed and output current is not bottle necked by any current/voltage limit

Description

When LD output current is set to be around 200mA or above, it is observed that the 3V3A power rail is not stable, which is visible on the 3V3A Power LED. Maximum voltage recorded is around 3.8V, which can cause some other hardware damages. This causes incorrect readings in PID, temperature and thus causes PID control loop to be unstable. The TEC current recorded was between 200mA and 100mA before the 3V3A goes unstable.

Cause of Problem

It is caused by the PD Mon input current being larger than the intended input range. Since there is back to back protection diode at the output stage of PD Mon, 3V3A is then being driven by the PD Mon output stage via the protection diode. Then, it causes the 3V3A rail to become unstable.

# Test environment Hardware Revision: rev0_3 Power: Via 12V Power Jack PD Mon Current Range is custom made to be 0 - 187uA. Laser Diode used: BFLD-974f-4HSM-NO PID is autotune-ed and output current is not bottle necked by any current/voltage limit # Description When LD output current is set to be around 200mA or above, it is observed that the 3V3A power rail is not stable, which is visible on the 3V3A Power LED. Maximum voltage recorded is around 3.8V, which can cause some other hardware damages. This causes incorrect readings in PID, temperature and thus causes PID control loop to be unstable. The TEC current recorded was between 200mA and 100mA before the 3V3A goes unstable. # Cause of Problem It is caused by the PD Mon input current being larger than the intended input range. Since there is back to back protection diode at the output stage of PD Mon, 3V3A is then being driven by the PD Mon output stage via the protection diode. Then, it causes the 3V3A rail to become unstable.
linuswck changed title from 3V3A is unstable when LD is on with >200mA current and TEC enabled to 3V3A is unstable if PD Mon Output Stage Voltage is larger than 3.3V 2024-07-19 14:52:16 +08:00
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Reference: sinara-hw/kirdy#47
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