0
\$\begingroup\$

I'm designing a circuit to provide a negative voltage rail in a battery for an ADC. I've decided to use a particular monolithic BCD Chip that can work as a step up/down/inverting controller and has an integrated switch.

I've designed the circuit inline with the data sheet inverting reference with the exception of using tantalums, a different shottky (30V 1A) and have a higher input voltage. At this point it doesn't appear that the circuit is switching (at all) from what I can tell, there is no oscillation on the timing cap pin or output, and Vout is measuring around +.3V. The chip is commanding 3W of energy which it appears to be dissipating itself.

Have I missed something here. I've substituted all components, so this is likely a design or layout issue I think. enter image description hereenter image description here

\$\endgroup\$
3
  • \$\begingroup\$ What is driving VCC, ie what is HYST_OUT? Then : if it's dissipating 4* the Abs Max power for the package, it's completely dead, and everything you can measure stems from that. Next time, power it from a supply current-limited to 50 or 100mA... \$\endgroup\$ May 25, 2021 at 12:43
  • \$\begingroup\$ HYST_OUT is the input - I am using a current limited supply, that was max observed \$\endgroup\$ May 25, 2021 at 13:03
  • 1
    \$\begingroup\$ I'm not sure you could have made that schematic any more confusing! \$\endgroup\$
    – Finbarr
    May 25, 2021 at 13:23

1 Answer 1

0
\$\begingroup\$

R5,R6 are connected incorrectly thus feedback voltage does not match 1.25V.

1 cut 2 jumpers needed. It should be obvious.

\$\endgroup\$
1
  • 1
    \$\begingroup\$ How so? Are they not identical to that in the reference? Are you seeing that on the schematic or the layout? Edit | I see it, the 12V reference is on the output of the voltage divider. Thanks for that :) \$\endgroup\$ May 25, 2021 at 13:06

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.