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leakage through negative input protection diode

Category: Hardware
Product Number: LT1785


I have an issue with batch 047 of LT1785 (marked LT 047 e3 1785 on the chip, assembled on my boards first half 2021). Previous LT1785 batches where OK and successive batches as well, but on this batch I have a high protection failure rate. I used on two production batches first a mixte of LT1785 batch 047 and earlier, then 047 and later, the issue is LT1785 batch related and not  my board batch related. In total the problem affects in the magnitude of 2000 units.

The failure triggers when there is a wiring error of the product inverting circuit GND and data - terminal:

- Converted to LT1785 voltages the chip will see GND=0V, VCC = -0.5V, B- = -22.5V

- on other batches I measure a 350uA leakage from GND to B-

- on batch 047 I observe 80mA "leakage" from GND to B-, the chip heats up and eventually smokes

This looks to me like an aftersale issue and not a technical request, so I wrote to customer.quality TRK:00334000142200 (CS-330036-F8H4B7), but they bounced me back here.

Can anyone help me identifying what is wrong with that batch ?


Cyril Holweck

added detail on the volume
[edited by: CyrilH at 11:27 PM (GMT -4) on 11 May 2023]