TPS92200: Check if TPS92200 could support 13.5V input and 13.2V output

Hi Jessica,

I am currently out of office. I will reply to you tomorrow. Thanks for your understanding.

Best Regards,

Steven

Hi Jessica,

May I understand why customer uses 13.5V as the input voltage? This is an input voltage value that I do not usually meet. Does this value have any variation? 

Best Regards,

Steven

Hi Steven,

Because customer has a DCDC before the LED driver device, and for the DCDC output, they need to connect to fan(maximum votage is 13.8V) and LED driver device. Since there would has 4pcs LED in the output of TPS92200, with maximum voltage 3.2V*4=13.2V(miniumum voltoge 3.1V*4=12.4V); And to met to let the input voltage between 13.2V~13.8V, so customer choice 13.5V as the input. 

If above condition can't met by our device, then could our device support 24V input(6s Battery voltage), and with 500mA continuous output current(customer would use analog adjustment of the output current), what is the efficiency under this kind of working condition? Customer has some concern for the thermal dissipation. Thanks a lot for you help to check.

Best regards

Jie

Hi Jessica,

Understood.

You should not use TPS92200 in this 13.5Vin and 13.2Vout condition. Please refer to Section 7.3.6 Maximum Duty Cycle from TPS92200 datasheet. It states that the TPS92200 device maximum duty cycle is able to go up to 99% (typical). You can also find this spec in Section 6.6 Timing Requirements from the datasheet. Therefore, 13.5Vin and 13.2Vout condition is at the edge of the maximum duty cycle (or even over the spec if we take into consideration the efficiency).

Jessica Wu74 said:

If above condition can't met by our device, then could our device support 24V input(6s Battery voltage), and with 500mA continuous output current(customer would use analog adjustment of the output current), what is the efficiency under this kind of working condition? Customer has some concern for the thermal dissipation. Thanks a lot for you help to check.

What is voltage range of the 6s battery?

Best Regards,

Steven

Hi Steven,

The input voltage range is 18V~25V.

Best regards

Jie

HI Jessica,

TPS92200 can work in Vin = 18V-25V, Vout = 13.2V condition if designed correctly.

If thermal performance is a concern, then customer can consider TPS922052 / TPS922053 for lower junction-to-ambient thermal resistance.

Best Regards,

Steven

Hi Steven,

Since customer change their power rail design, and they decided to give 12V input to TPS92200, so i recommend them to use 2 pcs of TPS92200 in this case, and for each output has 2 LEDS(output voltage is between 6.2V~6.4V), total 4 LEDS, the output current is 300mA. Below is customer schematic design, could you possible help to give a review of customer schematic design? Thanks a lot for your support again.

TPS92200_sch.pdf

Best regards

Jie

Hi Jessica,

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

Best Regards,

Steven

Hi Jessica,

Please refer to my comments below:

• Please use smaller inductor. Please be noticed that "For TPS92200, TI suggests that the inductor current ripple be larger than 300 mA to assure loop stability. If the calculated inductor current ripple is less than 300 mA, TI suggests a smaller inductor." You can refer to Section 8.2.1 from the datasheet for this information.
• If the above 300mA inductor current ripple requirement is to be met, can the customer accept such large output current ripple if no output capacitor is placed? If not, please let them add some output capacitors.
• I see customer currently uses one TL431 in the design to provide the reference analog voltage. Does the customer want to use the TL431 to fine-tune the output current for each driver? If not, I would recommend customer use TPS92200D2 version since the 1.2V output from the TL431 circuit will also introduce some variation if using TPS92200D1 version.

Best Regards,

Steven

Hi Steven,

Since for normal work condition, customer would keep the output current =350mA to drive the LED(LED peak current is 500mA), then if the system current should be limited to 500mA, then, could the L=6.2V*(13.2V-6.2V)/(13.2V*0.3*0.5A*1MHz)=22uH, could you please kindly help to  check if this calculation is correct?

Or if customer could choice a smaller inductor, could your possible share a capacitor value to start with? 

Because customer need to use analog dimming to use a voltage to set the output current to 350mA, so we recommend them to use TPS92200D1. Seems TPS92200D2 can't support analog dimming. If customer still need to use TPS92200D1, we could recommend them to use a higher accuracy TL431 in their system.

One more question from customer side is if they consider to change the  input voltage to 24V and with 4pcs LED(12.4V~13.2V) in output side, then if the inductor value L=13.2V*(24V-13.2)/(24*0.3*0.5A*1MHz)=40uH? 

Thanks a lot again for your support to double check.

Best regards

Jie

Hi Jessica,

Regarding the two calculations, please be noticed that "For TPS92200, TI suggests that the inductor current ripple be larger than 300 mA to assure loop stability. If the calculated inductor current ripple is less than 300 mA, TI suggests a smaller inductor." Customer should use inductor current ripple > 300mA for calculation. You can refer to this E2E thread for the considerations on >300mA inductor current ripple and K_IND parameter.

Jessica Wu74 said:

Because customer need to use analog dimming to use a voltage to set the output current to 350mA, so we recommend them to use TPS92200D1. Seems TPS92200D2 can't support analog dimming. If customer still need to use TPS92200D1, we could recommend them to use a higher accuracy TL431 in their system.

Actually TPS92200D2 can also support analog dimming.

Best Regards,

Steven