TPS61500: Less current output than expected

Sudheendra Hegde

Prodigy 40 points

Part Number: TPS61500

I have built a circuit similar to the TPS61500EVM board. Schematic is attached with this.tps61500evm-schematic.pdf

The problem with the circuit is, current flowing through the LED is very less with the following components:

Rfb = 0.22ohm

Vin = 5 to 9V

OVP set to 13.5V (100k and 10k)

Vf (LED) = 12V

I (LED) (max) = 1000mA

Also the voltage at pin FB is never 200mV. It is always below 120mV. Is is because of the compensation capacitor? Or is there anything wrong with the circuit?

Thanks in advance.

Regards,

Sudheendra H

over 6 years ago

0 Sean Zhou over 6 years ago

TI__Mastermind 22745 points

Hi Hegde,

So you have left the DIMC pin open or connected to a 1uF capacitor? And what's your PWM signal. Please attach the waveform with the VIn, Vsw, Vout and VFB signal, I need to look the waveform to check the problem.

Regards

Sean

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

TI__Mastermind 22745 points

Hi Hedge,

form your schematic, you have just connected 10kohm resistor to the OVP pin? where is the 100khm resistor?

Regards

Sean

0 Sudheendra Hegde over 6 years ago in reply to Sean Zhou

Prodigy 40 points

DIMC pin connected to 1uF (using a jumper).

PWM signal is of 100% duty cycle (5V).

Here is the zipped folder containing wave-forms.

3566.Waveforms.zip

0 Sudheendra Hegde over 6 years ago in reply to Sean Zhou

Prodigy 40 points

100kohm resistor is connected using a female header. This is done to easily change OVP setting while testing different LED.

0 Sean Zhou over 6 years ago in reply to Sudheendra Hegde

TI__Mastermind 22745 points

HI Sudheendra,

Here are some suggestions for you:

1. It since that the device doesn't work properly, I suggest you increase the OVP setting to a higher value(18V) and test again;

2. Change the compensation capacitor C4 to 220nF or 47nF and test again;

3. Apply our TPS61500EVM http://www.ti.com/tool/tps61500evm-369 and test with your application spec;

Regards

Sean

0 Sudheendra Hegde over 6 years ago in reply to Sean Zhou

Prodigy 40 points

Hi,

Increasing the OVP setting to higher values did not help but changing the C4 helped (two 100nF in parallel). Now the current flow is as expected but it is so only at Vin = 3.2V or Vin higher than 8V. Also Enable does not work properly with Vin = 9V. The LED keeps glowing (with nearly half the set current) when Enable is at GND and glows with full brightness when Enable is tied to Vin. Enable works as expected when the Vin is below 6V.

Any method to solve these issues?

Thank you.

0 Sean Zhou over 6 years ago in reply to Sudheendra Hegde

TI__Mastermind 22745 points

Hi Sudheendra,

I guess it may trigger the OCP, could you measure the waveform of current through the inductor? Or you can try to increase the RFB value to decrease the output current and observe whether this issue still exist or not.

Regards

Sean

0 Sean Zhou over 6 years ago in reply to Sudheendra Hegde

TI__Mastermind 22745 points

Hi Sudheendra,

How about the update status of your project? Have you solved your problem?

Regards

Sean

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TPS61500: Less current output than expected