TPS61169: TPS61169, driving backlight 21V and 160mA

Vitali Lach

Part Number: TPS61169
Other Parts Discussed in Thread: TPS61500

Dear Sirs and Madams,

our customer like to change the display type in his system, so I have to check the feasibility. I would appreciate your help: is that possible to drive the backlight with 21V and 160mA load current from 3,3V input? Please check the attached picture with display backlight requirements. I my breadboard setup a achieve only 110mA at 19V bei 100% PWM circle, I also can't find those limitations in the datasheet.

Best Regards

Vitali

over 2 years ago

+1 Hardy Wu over 2 years ago

TI__Genius 12915 points

Hi Vitali,

TPS61169 have 1.2-A current limit for internal switch MOS. As following simple calculation, assuming the efficiency is around 90%, we can get input current around 21V * 160mA / 3.3V / 90% = 1.131A. Plus current ripple at inductor, let's say 200mA, your condition is very margin and have high risk being limited.

The efficiency when boosting voltage from 3.3V to 21V is also not good. I suggest you could increase your input voltage level.

Here is another device TPS61500 with higher switching limit you could take a look.

0 Vitali Lach over 2 years ago in reply to Hardy Wu

Expert 1120 points

Hello Hardy Wu,

thanks for your explanation and your proposal. Unfortunately we only have 3,6V as the battery voltage in the system. I just tried the reference schematic for TPS61169 in TINA TI, could you please tell me why I cannot reach 160mA and 21V with 5V as the input voltage? Please see the attached simulation file.

Best Regards

VitaliTPS61169_Edit_TI-Forum_04.TSC

+1 Vitali Lach over 2 years ago in reply to Vitali Lach

Expert 1120 points

I think I found it. This is soft start function, some kind of delay. Sorry, my bad. But 3,6V input supply is not as good as the 5V supply case, that would be better.

0 Frank Qiu over 2 years ago in reply to Vitali Lach

TI__Genius 15776 points

If Hardy has solved this issue, i will close this thread.

0 Vitali Lach over 2 years ago in reply to Frank Qiu

Expert 1120 points

Hello Frank,

please wait with closing whis thread. I've got another question regarding simulation file attached here. Assuming input voltage to 3,6V, I see that changing the generic diode to a Shottky diode (MBRD320) makes the schematic inoperable (not enough output current). I cannot understand why, because Shottky diode is actually faster than ordinary diode, it isn't? Can Hardy please answer here?

PS: In our project we have B340A-13-F as Shottky diode on PCB, and it's working well.

Best Regards

0 Frank Qiu over 2 years ago in reply to Vitali Lach

TI__Genius 15776 points

hardy please keep following this case

0 Hardy Wu over 2 years ago in reply to Vitali Lach

TI__Genius 12915 points

Hi Vitali,

Where you see the statement of 'hanging the generic diode to a Shottky diode (MBRD320) makes the schematic inoperable'? I think Shottky diode have better performance for boost circuit.

0 Vitali Lach over 2 years ago in reply to Hardy Wu

Expert 1120 points

Hello Hardy,

the schematic is working, but it doesn't reach the 160mA output current. That happens if you change the diode to MBRD320. I just wanted to understand that fact. We will probably use TPS61500 in this case. Unfortunately I cannot find any simulation models for TPS61500 or calculation spread sheet, is that right?

Best Regards.

+1 Hardy Wu over 2 years ago in reply to Vitali Lach

TI__Genius 12915 points

Hi Vitali,

Yes TPS61500 do not have a simulation model.

0 Vitali Lach over 2 years ago in reply to Hardy Wu

Expert 1120 points

OK, thank you for that, Hardy.

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TPS61169: TPS61169, driving backlight 21V and 160mA