DRV8703-Q1: How Does Doubler Charge Pump work, why is this better than using bootstrap capacitor, is there any restriction on using charge pump

Rinya Uchiha

Part Number: DRV8703-Q1

Hello,

I am trying to find a gate driver that would improve/work for my project. Right now my gate driver is using bootstrap capacitors. I found out a lot of the gate drivers have integrated charge pumps, but they don't have many details on the doubler charge pump. So I found a TI document explaining the charge pump and was not fully understanding it and tried to simulate this circuit with LTspice to understand the circuitry better. And I am still a bit not understanding the circuit that well.

So I would like to know more detail about the charging pump if there are any other documents that I can read about.

I also want to know the pros and cons of using a charge pump and bootstrap capacitors.

Best Regard,

Rinya

over 2 years ago

0 Keerthivasan Kumanan over 2 years ago

TI__Mastermind 18425 points

Hi Rinya,

I have attached another charge pump block diagram below:

The charge pump works can be broken down into two cycles. In the first cycle when the low side switch is on the charge pump capacitor charges up to VM.

In the second cycle when the high side switch is on then there are few things to consider. The capacitor doesn't like to change voltage instantaneously, so to maintain VM across it for the voltage on the CPH node is force to 2Vm.

The same thought process can be applied to the diagram you have attached above. The yellow line is the capacitor charging up when the output of the timer is zero. When the output of the timer is 1, the voltage at the boot node goes to 2Vcc (red).

The difference between bootstrap capacitors and charge pump is that the bootstrap capacitor uses the driving stage FETs as the switch. It is the same principles, but it is dependent on the frequency of operation and the duty cycle. With a bootstrap capacitor it is also going to be hard to operate at 0% or 100% duty cycle. In the case for the charge pump, the operation of it is independent of the driver FETs. This allows for continuous operation even in the 0% or 100% duty cycle case.

Best,

Keerthi Kumanan

0 Rinya Uchiha over 2 years ago in reply to Keerthivasan Kumanan

Prodigy 80 points

Hello Keerthi,

Thank you for your reply.
Is there any limitation on the power delivery of the MOSFETs using a charge pump, as all TI gate drivers with charge pumps are limited to low source and sink current? Also, in the configuration you showed, how does the bootstrap capacitor-discharge, as it seems that even when the high-side MOSFET is ON, the capacitor is always maintaining the same voltage.

Best Regards,

Rinya

0 Keerthivasan Kumanan over 2 years ago in reply to Rinya Uchiha

TI__Mastermind 18425 points

Hello Rinya,

You don't want the capacitor to discharge and lose too much of its voltage. The discharge of the bootstrap capacitor occurs when you charge up the Cgs of the high side FET. The source and sink current really depends on the FETs themselves and not really the charge pump.

Best,

Keerthi

0 Rinya Uchiha over 2 years ago in reply to Keerthivasan Kumanan

Prodigy 80 points

Heller Keerthi,

Ah, I see. Thank you for your reply.

I am not sure if I should ask this question here, or if should I make another forum. It is not related to the charge pump, but it is still the same model.

I am trying to simulate the gate driver on Altium, using the pspice model that was downloaded from TI website. I got this error that I couldn't resolve it "Parameter v: Component DRV8701E_TRANS.E_ABM13: Unknown symbol "V (VM1)"".

best regards

Rinya

0 Keerthivasan Kumanan over 2 years ago in reply to Rinya Uchiha

TI__Mastermind 18425 points

Hello Rinya,

The PSPICE team at TI knows more about this, so I am going to route this to them.

Best,

Keerthi

0 Rinya Uchiha over 2 years ago in reply to Keerthivasan Kumanan

Prodigy 80 points

Hello Keerthi,

Thank you, appreciated!

Rinya

0 JC Zhu over 2 years ago in reply to Rinya Uchiha

TI__Mastermind 37520 points

Hi Rinya,

We are looking at this.

-JC

0 JC Zhu over 2 years ago in reply to JC Zhu

TI__Mastermind 37520 points

Hi Rinya,

would you please try this model file? DRV8701E_TRANS_0.LIB

I do not see E_ABM13 in it but it simulates fine:

Thanks,
JC

0 Rinya Uchiha over 2 years ago in reply to JC Zhu

Prodigy 80 points

Hello JC,

Sorry for the super late reply, I haven't gotten to work on this until now.

I downloaded the spice model library that you sent and selected the "DRV8701E_TRANS" model name. After that, I mapped the schematic pin corresponding to the model pin.

I am still having this error. Due to this error, I am still unable to simulate it.

The schematic is very simple with the gate driver driving an H-bridge, I didn't have any programmable pin connected for now to keep it simple, only the PWM input which is connected with Pulse Source.

Best,

Rinya

0 JC Zhu over 2 years ago in reply to Rinya Uchiha

TI__Mastermind 37520 points

Hi Rinya,

Would you pelase share the .LIB file?

-JC

0 Rinya Uchiha over 2 years ago in reply to JC Zhu

Prodigy 80 points

Hello
JC,

These are the .LIB file I used:

1) 1348.DRV8701E_TRANS_0.LIB (downloaded from you)

2) DRV8701E_TRANS.LIB (downloaded from https://www.ti.com/product/DRV8703-Q1?HQS=app-null-null-widget_pf-manu-pf-ElectronicSpecifier-eu#design-development Design Tool & Simulation)

Both of them when I simulate it on Altium would have the same error that is preventing me to simulate.

Best,

Rinya

I just noticed for the #1 .LIB file, the one that I downloaded from you, the file name changed when I uploaded the file to here. I am not sure if that is an issue

0 David Larkin over 2 years ago in reply to Rinya Uchiha

TI__Mastermind 20460 points

Hi Rinya,

Can you confirm that you are trying to run a PSpice simulation in Altium?

David

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DRV8703-Q1: How Does Doubler Charge Pump work, why is this better than using bootstrap capacitor, is there any restriction on using charge pump