TPS1641: CAN THE CAPACITOR SELF DISCHARGE?

Hi Sun,

Please share test waveforms of VIN, VOUT, dV/dt voltage and Input current during startup

BR,

Rakesh

hi,dear.

Sorry for my late. I find a strange thing. When the chip pin10 is connected to the capacitor array ,the board is abnormal. I measured the pin of  VIN and VOUT, the waveforms is displayed as below:

The VIN (yellow line)is constant, Vout (cyan line) will decrease slowly, meanwhile the dVdt pin is about 0v. 

When I disconnect the capacitor array, the TPS16412 seems to work fine, VOUT(yellow line) remains 12V (because Vin is 12V), dVdt pin(cyan line) is about 5v. The normal picture is as below:

The reason that I choose TPS16412 is for its ability which can charge large capacitor slowly and can't influence the system. 

What should I do to solve the problem?

Thanks!

Thanks you.

But unfortunately it is not very clear. can you share all VIN, VOUT, dV/dt voltage and Input current during startup in a single scope shot. like Figure 9-3 in data sheet.

Why 23mF is needed ? Have you verified the startup with design calculator ?

BR,

Rakesh

Sorry for my poor equipment. I can't measure the input current.

I used 23mF to produce 10A current in the 50ms to explode the powder in order to release parachute.

I used the tool of  design calculator. When I fill in the row 7 (Cout) with 23000.00, some contents becomes to  #REF!

Does it mean that the chip doesn't support so large volume capacitor?

In addition if there is the TPS16412 demo board in your laboratory, you can experiment it just only charge the capacitors to verify the chip's ability or measure the input current.

thank you very much!

Thank you for your recommendation, sir.

Before I will use the new chip in next board version, can you tell me the maximum volume that TPS1641 can support? Maybe I will use TPS1641 some day.

Thank you again.

it depends on your ambient temperature. Please use the same calculator to check on the max value.

Hi, dear.

As to TPS1641, I has another question. That is why the voltage of the OUT can decrease slowly?

Please look the picture as below(similar to my situation),  Vin is always present(12v), and OUT is also 12V at first. Because  there are just only many capacitors, no any load and the FET's body diode blocks OUT flow to VIN. I think there is no way to release the OUT. Is my understanding right?

Why the voltage of OUT can decrease slowly?

Thank you!

Hi, dear.

There is no load and if the self leakage of Cout is so large, the voltage of capacitor is impossible the same to VIN at the beginning. After the voltage value of Cout is equal to Vin, then Cout decrease slowly.

ok.

What is the rate of discharge of Vout ? I mean the falling slope Vout/dt ?

hi, dear.

In these days,  i have done some simply test to verify the capacity of Tps16412 which include vary its input voltage and change the output capacitors numbers per the calculator tools. The other situation is the chip pin10 just only connect to capacitor , no other load.

For example, when the chip connect with a 1000uF capacitor and its input voltage is 12V, the problem of decreasing voltage can happen.  I measured the voltage with multimeter and its digital reading changed rapidly.

In one or two minutes, the digital reading can become 2V or below. 

Just to be sure, when I change the input voltage to 6V and connect a 220uf capacitor, the chip work well and  capacitor's voltage can stay stable.

Hi Sun,

Understood. We will check with the design team, verify at the end and get back to you. Please allow some time. 

BR,

Rakesh

Hi Sun,

Few questions:

Are you disabling the device by EN=LOW ? or whether the device is turning-off by itself ?

Is there any load (even in disable state) connected at the output apart from capacitance ?

BR,

Rakesh

hi, dear.

Are you disabling the device by EN=LOW ? or whether the device is turning-off by itself ?-----No,  EN is always connected to 3.3V and the chip is always enable. My design is shown at the beginning.

Is there any load (even in disable state) connected at the output apart from capacitance ?-----No, there is no any load except a 1000uf Capacitor.

You can easily find the phenomenon if the chip input voltage is 12V and output capacitor is 1000uf. Meanwhile the voltage of dvdt pin is about 0V in abnormal situation and can become 5v in normal situation. 

Thank you

Hello Sun,

Greetings.

Can you check the FLT flag?

It looks like IN to OUT Short Detection would have happened.

TPS16410, TPS16411,16412, TPS16413 have IN to OUT short detection feature.

You can choose other variants (TPS16414 to TPS16417) which doesn't have this.

Thank You

Amrit