TPS61194: Channel (led string) short circuit fault is not reported at every failure instance

Chaitanya Dasari

Part Number: TPS61194

In TPS61194, when there is a short circuit (Vout shorted to OUTx),it is observed that fault is not reported all the time.

Test Conditions:

Input Voltage=12v

RIset = 49k

Rfset = 160k

PWM=100%

Feedback: R1= 470k, R2=130k

(Out1,Out2) channels are shorted

Vout= 15V

over 6 years ago

0 Sean Zhou over 6 years ago

TI__Mastermind 22745 points

Hi Sir,

Fault pin is open-drain structure you need to pull it up and try again.

Regards

Sean

0 Chaitanya Dasari over 6 years ago in reply to Sean Zhou

Intellectual 280 points

In my design VDDIO is 1.8V and Fault pin is pulled up to 1.8V through 10k resistor.

0 Sean Zhou over 6 years ago in reply to Chaitanya Dasari

TI__Mastermind 22745 points

Hi Chaitanya,

Could you please provides some waveforms for this situation?

Regards

Sean

0 Chaitanya Dasari over 6 years ago in reply to Sean Zhou

Intellectual 280 points

Hi Sean

Please refer the image of my simplified schematic design model which is attached below.In my design OUT1,OUT2 are shorted and a led string is connected to it from VOUT. Similarly OUT3,OUT4 are shorted and a led string is connected to it from VOUT.

Test Conditions:

Input Voltage=12v

RIset = 49k

Rfset = 160k

PWM=100%

Feedback: R1= 470k, R2=130k

VDDIO is 1.8V and Fault pin is pulled up to 1.8V through 10k resistor.

I Connected a SPST switch (SW) across Vout and OUT3,OUT4, Which is open Initially.So when I close the SW, It is similar to LED string short circuit condition and Channel (led string) short circuit fault is not reported at every failure instance.

I am also attaching the waveform where fault is reported but I cant capture the waveform of instance where fault is not reported even though there is a fault existing.Because You know that TPS61194 has adaptive output voltage control based on the LED current sink headroom voltages.Where the output voltage never goes to zero if there is a short on one channel.So there will be not valid information to capture at the moment where fault is not reported.In average I repeated the above fault condition 10 times in which 3 times the fault is not reported.