Help me understand this circuit - E-Paper TFT power management

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I'm looking at using this screen for a project - https://www.digikey.com/en/produ...

I'm not really sure what's going on in the picture I attached from page 29 of the datasheet, seems like some sort of a charge pump, boost converter combo...? I couldn't much info in the datasheet about VGH and VGL pins that it's connected to either. Hoping someone can explain the purpose and/or how this circuit functions.

Thanks

 

Datasheet - https://www.orientdisplay.com/wp...

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Last Edited: Sat. May 14, 2022 - 03:17 AM
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See Table 5 on page 6.

 

Indeed, GDR is Mosfet gate drive. It appears to require positive and negative supply voltages, VGH and VGL,  and a logic supply voltage, VCI, of 3.0V. The command table on page 13 seems to show different configuration settings for different VGH and VGL values. That circuit does appear to be a charge pump.

 

Jim

 

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They draw it as a twisted mess, if you draw it normally it makes more sense, though not total , since they don't say where VSH1 and VSH2 com from.

 

anyhow C2 & C4 are filter caps & can be "ignored" (assume a nice steady VH & VL are made).

 

C3 is the pump

When the fet is on, the inductor is probably pulled close to gnd (ignoring the current monitor resistor).  The inductor will have a positive voltage then

When the fet is off The D2 side of C3 is clamped to 0.7V above gnd & charges positive.

When the inductor lead swings negative entire C3 voltage pulls D3 negative to give a negative voltage.  

If the fet is off for the longest time C3 will charge to Vchip (vchip through inductor through D2 to gnd).  Lower time will reduce thisaamount

The average inductor voltage (over cycles) must always be zero.  The fet duty cycle will play into this to skew the % time the inductor is positive and % negative.  And the inductor voltage amounts must reflect this to give an avg zero .

That's as far as I took it.    

 

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That circuit is simply a twisted variation of the bootstrap circuit commonly found in low input voltage converters, where the diodes have been reversed.

Here's an example: https://www.analog.com/en/technical-articles/bootstrapped-synchronous-boost-converter-operates-1-8v-input.html

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That circuit is simply a twisted variation of the bootstrap circuit commonly found in low input voltage converters, where the diodes have been reversed.

Kinda sorta...here they are generating 2 voltages, and they are using zeners , maybe to also give some clamping levels?

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!