WEBENCH® Tools/TPS7A4001: LDO output voltages controlled by DAC

koho

Part Number: TPS7A4001

Tool/software: WEBENCH® Design Tools

Hi,

I am looking at https://e2e.ti.com/blogs_/archives/b/precisionhub/archive/2016/09/02/give-your-voltage-regulator-the-margin-it-deserves

I tried to simulate this. But, my output doesn't go higher than 5V. In theory, Vout = Vref*(1+R1/R2), when DAC output equal to 0, then how is it goes to 5.5V? I want to get the same results as Figure 5 in the link.

I also tried to use this equation with Vref=0.8V then, I lost the upper margin when I computed R1 based on R2. This is almost fixed wrt Equation (1) and (3)

Would you correct me if I am wrong? and also if possible, would you share the simulation file to test?

Thanks

koho

over 3 years ago

0 Jason Song over 3 years ago

TI__Mastermind 23361 points

Hi Koho,

Are you trying to adjust the output of the LDO using a DAC as shown in Figure 3? Will you post your TINA schematic (the actual schematic file, and the screenshot) for me to review?

Regards,
Jason Song

0 koho over 3 years ago in reply to Jason Song

Prodigy 220 points

Yes, I want to adjust output voltage using DAC.

I basically tried to copy all from Figure 4. Bit codes were all high and all low to see all range of output.

SBVM143A_koho.TSC

0 Jason Song over 3 years ago in reply to koho

TI__Mastermind 23361 points

Thanks for sharing the file, please allow some time to play with the simulator, I will get back to you by Friday.

Jason

0 Jason Song over 3 years ago in reply to Jason Song

TI__Mastermind 23361 points

Hi Koho,

To verify this function, it's better to use a DC source to replace the DAC during debugging. You may then run DC transfer characteristic sims by varying the VG1. Please see the results also in the screenshot. As you can see, when VG1 is varying from 0 to 2.5V, the output of the LDO is also changing from 5.2V to 4.2V. The TPS7A40's reference voltage is 1.18V, so it is slightly lower than the one showed in the example.

Regards,
Jason Song

Power management

Power management forum

WEBENCH® Tools/TPS7A4001: LDO output voltages controlled by DAC