Discussion on the Effectiveness of S12ZVM Charge Pump Circuit

[maxxu]

Hello everyone！

      Recently, the S12ZVML31 chip has been debugged. Charge Pump circuit is used in order to achieve high duty cycle (upper arm chopper, lower arm shutdown) in independent PWM mode. According to the manual, 100% PWM can be achieved. The signals of CP and VCP are normal, but the 22V voltage of VCP is not supplied to VBS.

The process is as follows

(1) Configure the circuit according to the manual

(2) Enabling charge pump

     GDUE_GCPE = 1; / / charge pump

     GDUCLK2_GCPCD = 2; //Fbus/32

     GDUCTR = 0x13; // blanking time

(3) Observing signal, starting charge pump, normal signal

                                                      CP   signal，785KHZ

                                                               VC   Psignal，22v about

(4) Observing that GDU signal (HG signal) is affected by charging period of bootstrap capacitor, and can not achieve 100% duty cycle.

         (a) HG waveform (blue) LG waveform (yellow), HG flat top waveform, 22V ,under light load. indicating that the electric quantity in bootstrap capacitor is enough to drive MOSFET.

        (b) At full load, HG waveform (blue) and HG voltage are obviously low, and the slant line is downward, indicating that the bootstrap capacitor power is gradually exhausted and not supplemented by the VCP power.

(5) Other evidences show that CBS motor without bootstrap capacitance can not start, which indicates that the VCP power has not come. The experimental results of using development board S12ZVML-MINIBRD are the same. When bootstrap capacitance is increased from 0.22uF to 1uF, HG signal is obviously improved.. However, in software, whether GDUE_GCPE = 1 or GDUE_GCPE = 0, it has no effect on HG signal.

     Now I suspect that the P2 transistor connecting VCP and VBS has not been opened, but I can not find the relevant settings in the register, nor in the code of the development board. I don't know why. Can some useful friends point out?

[danielmartynek]

Hello,

Could you please specify the BUS frequency, PWM frequency and duty cycle?

Thank you,

BR, Daniel 

[maxxu]

hello，

BUS frequency about   200hz（8-pole motor 3000 rpm）     

PWM frequency  16KHZ

duty cycle   about 95% 

In addition, if VCP is effective, three bootstrap capacitors can be removed, but in practice, even if the charge pump function is enabled, the bootstrap capacitor can not be removed, otherwise the circuit will not work.

By the way, in order to make the output current as continuous as possible and reduce EMC, the limiting current resistance of HG LG and MOSFET gates is 510 ohms.

In the last post, when duty increases, the HG signal goes downward obliquely, because the resistance consumes the power in the bootstrap capacitor and is not supplemented by the power from VCP.

My English is not very good. Please forgive me.

 Thank you very much.

[pachamatej]

Hello,

please can you specify the mask set of the S12ZVM? It is printed on the chip next to the chip "name" in format of 0N95G, 1N95G, ...

And an additional info: what is the CPU clock settings?

Thank you,

Matej

[maxxu]

hello

     The chip I tested was S912ZVM16(1N14N),P912ZVML12(1N95G).S912ZVML32(1N95G)

     he CPU clock setting reference demo，fcore=50MHZ,fbus = 25MHZ，used IRC1M

     I don't think that's important. I just want to know if bootstrap capacitance can be removed after charge pump is started. I think the normal situation is OK.

Thank you,

[danielmartynek]

Hello,

The charge pump is connected after the blanking time during which the gate is opened using the bootstrap capacitors.

So, you need to have the capacitors anyway and charge them before it is switched to 100% duty-cycle.

I don''t see any reason why wouldn't the charge pump connect after the blanking time though.  

BR, Daniel

[maxxu]

hello，

Thank you for your reminder。

The problem was found. Tblank was set incorrectly. I turned off the P2 transistor.

[steven_zhang]

if the tblank is ok，will  the P2 be opened ,or there is some control bit to open it ?