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LT4363 - VCC above output voltage, excessive supply current


I am testing circuit with VCC higher than output voltage and noticed higher current consumption in certain conditions. Tested circuit is below:

V_SUPPLY was 12V, and tested V_IN was 5V, 3.3V, 2.5V, 1.8V and 1.2V. FB divider for OVP was selected by connecting proper resistor to OUT. 1.8V and 1.2V was ok in terms of current consumption, but when V_IN was higher than 2.1V and NMOS was ON, the IC was drawing excessive supply current, ~5mA from 12V line (datasheet states 1.2mA max supply current).
Higher supply current is present only when NMOS is ON.
I also measured that supply current returns to nominal (1.2mA) when V_IN voltage rises to VCC-0.5V. It was tested when V_SUPPLY was equal to 10V (VCC=9V) and V_IN initially was 0V, then V_IN was turned on. While V_IN was ramping up and exceeded 2.1V, supply current rised also up, and VCC dropped to 5V (since it is powered through 1k resistor 5mA caused 5V voltage drop) and when V_IN rised to about 4.7V supply current dropped to 1.2mA, and VCC rised to initial 9V as shown below.

Also it was simulated in LTSpice, but it doesn't show the same behaviour.

Things I also checked:
 - Replaced LT4363-1 to a new part, same behaviour

- Checked current flowing to SNS and OUT, to SNS 22uA, to OUT 110uA, while supply current is nominal and 350uA while supply current is excessive. (V_SUPPLY=12V, V_IN=5V)

- Removing C3 from GATE pin - now it shows dependency of V_IN, V_SUPPLY sequence, but only if V_IN is above 3.2V. If first comes up V_IN (above 3.2V) and then V_SUPPLY (12V) - supply current is nominal, but when first comes up V_SUPPLY (12V) and then V_IN - supply current is higher (5mA). It doesn't work for V_IN=2.5V.

- Disconnecting OUT and SNS lines from R1 and then connecting through 22 ohm resistor to GND - current supply dropped down to 1.2mA, while NMOS was still ON, but jumped up again to 5mA when it was connected to R1 again. (V_IN=3.3V, 2.5V, 5V, V_SUPPLY=12V)

The last point suggests that there is something going on with those SNS and OUT pins, however I cannot see on block diagram what can cause this behaviour.

Could you tell me what can cause this higher supply current consumption? Is there any way to prevent it for described application?

  • This is a non-standard application. The Icc current specified in the datasheet is for the common application where SNS and OUT are at a voltage similar to VCC during normal operation. Any analog IC will have a different supply current depending on which circuit blocks are getting switched on/off or if a particular block is working harder depending on pin conditions. In this case, it is most likely due to the charge pump block taking more current through the VCC pin.

  • Thank you for reply. It turned out that ENOUT pullup resistor (R9) had wrong value on PCB - 100 Ohm instead of 100 kOhm and this low resistance caused high current flowing to ENOUT pin.

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