TPS923654: TPS923652DRRR: Schematic for review

Hi,

Our expert is out of office today and will give you feedback when comes back.

Hi Udesh,

May I understand what is your input voltage?

Best Regards,

Steven

HI Steven

the input voltage is 12V

Hi Udesh,

What is the required output current? I see you set the max current at 1A in your schematic. However, the above light bar shows a typical current of 540mA.

Best Regards,

Steven

HI Steven 

Yes the typical current requirement is around 540mA only but maximum it will go till 700-800mA. So that's why we have set as 1A

Hi Udesh,

Udesh Singla said:

Yes the typical current requirement is around 540mA only but maximum it will go till 700-800mA.

If this is the case, then I would recommend you set the max current of the circuit to be this 700-800mA. Otherwise, your light bar may get 1A output current with the current setting and may be damaged.

For other components, please refer to my comments below:

1. If the FAULT pin is unused, you should change the R1760 to 0ohm. You can refer to this E2E FAQ - [FAQ] How to deal with the unused FAULT pin of TPS923655 / TPS923654 / TPS923653 / TPS923652? - Power management forum - Power management - TI E2E support forums
2. My estimation shows that the temperature rise will be very large based on your current setting. Please use smaller switching frequency to reduce the switching loss (Please adjust your inductor accordingly). For Vin = 12V, Vout = 33V, this will create a rather large duty cycle and the conduction loss will be large. However, the conduction loss cannot be changed, so we need to reduce the switching loss to improve the thermal performance of the device. Also, VSON package is recommended here for better thermal performance.
3. The value of OVP resistor divider is not correct. Please refer to this E2E FAQ - [FAQ] How to design the OVP resistor divider for TPS923655 / TPS923654 / TPS923653 / TPS923652? - Power management forum - Power management - TI E2E support forums
4. You should place a 100nF decoupling capacitor between VIN and GND. Please place this capacitor close to the VIN pin.
5. The thermal foldback threshold may be too small currently. You can change R1761 to 0ohm during your initial test to disable the thermal foldback function and decide & adjust the threshold value later. (You can refer to this E2E FAQ - [FAQ] Is there a way to disable the thermal foldback function of TPS923655 / TPS923654 / TPS923653 / TPS923652? - Power management forum - Power management - TI E2E support forums)
6. The capacitance value of C1884 is too small. Please refer to Section 9.2.1.2.5 Other External Components Selection from the datasheet to see how to design the C_SENSE capacitor.
7. The correct part you should use is TPS923654 or TPS923655 since they have larger switching FET cycle-by-cycle current limit that fits your application.

Best Regards,

Steven

HI Steven 

I have updated all the comments except OVP resistor values, I have calculate the OVP resistor value as per formula suggested in theE2E link. i.e (Vout_max * R_OVP2 / (R_OVP1 + R_OVP2) < 1.1V. ).

But my values is coming too high, Rovp2 is 1M and Rovp 1 is 30M so the value is 0.96, so can you please check and help to get the Rovp 1 and Rovp2 values, My output voltage is 30V.

Hi Udesh,

our Expert will reply once back to the office.

BR

Monet Xu

Hi Udesh,

The ratio of 30Mohm vs 1Mohm satisfies the formula, but we do not recommend resistors with too large value here as the leakage current of the OVP pin may cause some problem if the values of the resistors are too large.

Please be noticed that the E2E FAQ has stated - "A rule of thumb is that you can design the sum of R_OVP1 and R_OVP2 to be around 1Mohm or 2Mohm and this normally would be a good start point. You can then adjust the values based on your test results." (A screenshot is shown below.)

Best Regards,

Steven

HI Steven

We have checked the rule and now the values is coming around Rovp2 as 50k and Rovp1 as 1.5M and its satisfy the formula also.

So kindly check and let us know if we can use these values.

Hi Udesh,

The nominal values are ok if your max output voltage is 30V. Please make sure you have taken into consideration the tolerance of the resistors.

Best Regards,

Steven

HI Steven

30V is the nominal voltage, the max voltage will be around 33V, so kindly suggest if we need to modify the values as per 33V or not. 

Hi Udesh,

As is stated in this E2E FAQ, to make sure your output current won't be affected by CV mode in all working condition, you should make sure Vout_max * R_OVP2 / (R_OVP1 + R_OVP2) < 1.1V. 

Since your Vout_max = 33V, this is too marginal. You should modify the resistor values to provide more margin.

Best Regards,

Steven

HI Steven 

Thanks for your reply, we have updated all the comments, please find the latest schematic attached, please review once and share the feedback.

VVDN_TI_ORBU_P2I7_BKLT_PWR_A0-53.pdf

Hi Udesh,

Steven Li said:

My estimation shows that the temperature rise will be very large based on your current setting. Please use smaller switching frequency to reduce the switching loss (Please adjust your inductor accordingly). For Vin = 12V, Vout = 33V, this will create a rather large duty cycle and the conduction loss will be large. However, the conduction loss cannot be changed, so we need to reduce the switching loss to improve the thermal performance of the device. Also, VSON package is recommended here for better thermal performance.

I do not see you made any modification regarding the above advice. Please double check.

Steven Li said:

You should place a 100nF decoupling capacitor between VIN and GND. Please place this capacitor close to the VIN pin.

I do not see you made any modification regarding the above advice. Please double check. C1871 is for power path decoupling, and you need another decoupling capacitor for VIN pin.

Also, the new Schottky diode on your schematic does not have enough current rating. Please double check.

Best Regards,

Steven

HI Steven

Please find the attached schematic for your reference we have updated all the comments except schottky diode, as of now schottky diode is 45V and our max output voltage is around 33V only so can you please check and let us know if this is correct or not.

VVDN_TI_ORBU_P2I7_A0-58.pdf

Hi Udesh,

Sorry. I am currently out of office. I will reply to you next Monday when I am back to office. Thanks for your understanding.

Best Regards,

Steven

Hi Udesh,

Sorry for the late response. Please refer to my comments below:

Steven Li said:

My estimation shows that the temperature rise will be very large based on your current setting. Please use smaller switching frequency to reduce the switching loss (Please adjust your inductor accordingly). For Vin = 12V, Vout = 33V, this will create a rather large duty cycle and the conduction loss will be large. However, the conduction loss cannot be changed, so we need to reduce the switching loss to improve the thermal performance of the device.

Again, please reduce your switching frequency and enlarge your inductor value accordingly to reduce switching loss. You currently set the switching frequency to be around 2.2MHz, which is too high.

Steven Li said:

Also, the new Schottky diode on your schematic does not have enough current rating. Please double check.

Again, the Schottky diode on your schematic does not have enough current rating. Please double check.

Best Regards,

Steven

Hi Udesh,

What I meant is the current rating but not the voltage rating of the Schottky diode.

Best Regards,

Steven

HI Steven

The max average current of the shottky diode which i am using is around 1A and the display average current is around 0.6A

So i think the shottky diode is fine.

Please find the below schottky diode part no which i am using

MPN:PMEG45T10EXD-QX

Kindly check and let us know if this is correct or not.

Also if you have any recommendation of the schottky diode part please share we will use the same part.

Hi Udesh,

Udesh Singla said:

HI Steven 

Yes the typical current requirement is around 540mA only but maximum it will go till 700-800mA. So that's why we have set as 1A

Sorry. I forgot you had told me that the maximum output current would be 700-800mA. If this is the case, then the current rating of the Schottky diode looks ok but a bit marginal.

If the maximum output current is 0.6A, then the current rating of the Schottky diode (1A from its datasheet) looks ok.

If the maximum output current is 1A, then the current rating of the Schottky diode (1A from its datasheet) is not enough.

Best Regards,

Steven