Charge Pump Block Question (TC1044SCPA)

[benny_profane]

For projects with a charge pump (e.g., TC1044SCPA) for (positive) voltage doubling, why is there a capacitor between pin 4 (CAP-) and pin 2 (CAP+) before connecting to another cap positioned on the cathode of the Schottky diode after pin 8 (V+). Unless there's a negative voltage conversion, is the cap between pins 2 and 4 necessary? Also, is pin 4 needed at all in voltage doubling applications? The data sheet shows it as an NC for multiplier use cases.

 

[Robert]

You are correct that the capacitor between pins 2 and 4 is unnecessary except when being used as an inverter. (NC to pin 4 as well)

It's another one of those things that has been handed down from circuit to circuit over time.

I'm guilty of leaving it in place myself on several circuits.... I remove it when I catch it.

 

[benny_profane]

Ah okay. That was throwing me off a bit. Thanks for the response.

 

[benny_profane]

Another question here: Why do some charge pump blocks use 1uF caps instead of 10uF for the pump/reservoir caps? Doesn’t the reduced value negatively impact charge pump efficiency?

 

[benny_profane]

For example, in the Soldat Distortion, all of the caps in the charge pump block (C18–21) are 1uF instead of 10uF. Is this simply to save space on the pcb?

 

[Robert]

I'm not sure what the benefit would be unless it was simply to streamline the BOM, there isn't a heck of a lot of difference in physical size between the two.

The only real "benefit" I can think of would be inrush current (or maybe to reduce the amount of time of pump-up), but neither of those seem to be enough of an issue to justify it.

I've also seen some circuits that use 47uF or even 100uF throughout.

The Creation Audio Labs MK.4.23 Clean Boost uses 1uF capacitors as well, but it uses a different charge pump.

 

[benny_profane]

I was thinking that it would provide more stability. If that’s not the case, I’ll stick with the BOM.

 

[christomania]

The Creation Audio Labs MK.4.23 Clean Boost uses 1uF capacitors as well, but it uses a different charge pump.

@PedalPCB do you know what is the charge pump used by MK.4.23 ?

Regards

 

[Robert]

@PedalPCB do you know what is the charge pump used by MK.4.23 ?

Regards

LT1026

 

[benny_profane]

Wow. Both SMD and THD are over $6 for the LT1026 at Mouser…and it maxes at 15mA.

 

[christomania]

Thank you @PedalPCB