WEBENCH® Tools/TPS40090: RC network of DCR current sensing

Ammar Afi

Part Number: TPS40090

Tool/software: WEBENCH® Design Tools

Hello,

I'm trying to understand the DC current sensing of the TPS40090 steady state simulation. According to the reading material when RDCR and CDCR are selected in such a way that the RC time constant is equal to the ratio of inductance and series resistance of the inductor, the voltage across CDCR will be directly proportional to the inductor current (IL)

Next, i'm using the TINA TPS40090 steady state simulation file to understand this concept further (as shown below). But when i probe at Vlpf, the voltage across the C45 is around 1.56V (refer waveform below). Isn't it suppose to be 43.8mV in order for it to get 25A for each phase (using formula of Vdcr=Iload X RL)? Attached is the simulation file. I'm running transient from 0 to 5mS. Thanks

over 4 years ago

0 Qian Chen over 4 years ago

TI__Mastermind 24075 points

HI Ammar,

Do you measure Vlpf to ground or Vlpf to Vout?

The voltage across C45 is the voltage between Vlpf and Vout.

Thanks

Qian

0 Ammar Afi over 4 years ago in reply to Qian Chen

Prodigy 110 points

Hi Qian,

Thanks for your response

I'm using the "invert arrow" probe to measure voltage across c45? by using this probe it will referred to ground instead of vout. am i right? how do i measure voltage of c45 and want it ro refer to vout instead? i can't use the voltmeter as it will only work on dc analysis not in transient analysis.

0 Qian Chen over 4 years ago in reply to Ammar Afi

TI__Mastermind 24075 points

Hi Ammar,

TINA model does not have differential probe to measure the voltage across C45.

The voltage on C45 is Vlpf minus Vout.

Vout is a DC voltage. So you can see Vlpf-Vout is equal to Rds*I during switching.

Thanks

Qian

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WEBENCH® Tools/TPS40090: RC network of DCR current sensing