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LTC7001 charge pump voltage collapses upon enable

Category: Hardware
Product Number: LTC7001
Software Version: n.a.

Hi,

I'm currently designing a high-side switch using the LTC7001, however it doesn't seem to able to get the MOSFET to conduct. After power on (INP = 0) the charge pump charges up the boost capacitor to 12V as expected, but when INP becomes high the BST voltage drops to about 3.2V and TGUP/TGDN stays connected to TS.
As shown in the schematic snippet VCC is set to 5V, with the UVLO set to 3.5V and no OVLO, the enable signal comes from a microcontroller and has 0 - 3V3 drive voltage. The INP pin is set high once, so no switching is involved.

Due to it having to drive a FET with a relatively high gate charge I've already tried placing a larger (10uF) bootstrap capacitor with an external bootstrap diode to no avail. Removing the FET completely also yields the same behaviour.

I've observed this behaviour on both prototype board I have and soldering on a new chip doesn't help either, this makes me believe that it is an actual design flaw in my schematic. The datasheet doesn't mention fault modes except for the UVLO/OVLO, do you have any pointers on how to proceed in the debugging process?

With kind regards,
Willem






EDIT: removed pictues uploaded twice
[edited by: Willemvdk at 3:36 PM (GMT -5) on 16 Nov 2023]