Author Topic: Boost converter voltage drop  (Read 923 times)

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Offline fedimakniTopic starter

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Boost converter voltage drop
« on: January 27, 2020, 08:44:28 am »
Hello
I used both the TPS610986 and TPS61291 boost converter in order to power a load that consume around 200mA in both situation (TPS610986 powering the load then use the TPS61291 to power the same load) the boost converter voltage drop down to around 0.45V. Both of them work correctly with load that consume 10-20mA but with higher load the voltage drop down i didn't understand the reason as the datasheet mention that both could work fine by supplying 200mA. ( I also tried a load that consume 100mA but i faced the same problem)
Input voltage: 3V
Output voltage: 3.3V
Could you please tell me how to fix it.
Thanks
PS: attached the schematic of both boost converter that I used
« Last Edit: January 27, 2020, 08:47:36 am by fedimakni »
 

Offline EEEnthusiast

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Re: Boost converter voltage drop
« Reply #1 on: January 27, 2020, 08:49:28 am »
for the TPS610986 , the recommended cap from VSUB to GND is 10uF whereas your schematic uses 1uF.
Can you also check with lowering the input voltage. Some boost converters behave strange when the output voltage is close to input.
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Offline fedimakniTopic starter

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Re: Boost converter voltage drop
« Reply #2 on: January 27, 2020, 08:58:18 am »
I am not using the Vsub as the mode pin is tied to ground. so it's deactivated. and the same problem occur with the second boost converter.
Even with 2V input voltage i still face the same problem
« Last Edit: January 27, 2020, 09:02:25 am by fedimakni »
 

Offline EEEnthusiast

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Re: Boost converter voltage drop
« Reply #3 on: January 27, 2020, 09:21:19 am »
can you tell the part number for the inductors used?
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Offline fedimakniTopic starter

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Re: Boost converter voltage drop
« Reply #4 on: January 27, 2020, 09:41:08 am »
VLS252010HBX-4R7M-1 for the TPS610986
MDMK2020T3R3MM for the TPS61291
 

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Re: Boost converter voltage drop
« Reply #5 on: January 27, 2020, 09:50:42 am »
How bad is the voltage drop?
can you share the layout layers. Some of the TI DCDC converters are very sensitive to layout.
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Offline fedimakniTopic starter

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Re: Boost converter voltage drop
« Reply #6 on: January 27, 2020, 10:01:56 am »
the layout is good, it's almost identical to the recommended layout in the datasheet
The voltage drop to 0.75V
 

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Re: Boost converter voltage drop
« Reply #7 on: January 27, 2020, 10:17:00 am »
The output traces seem way too thin and can drop a bit, but not to 0.75V.
Did you probe at the cap at the output of the DCDC?
Looks like the DCDC is not able to get into PWM mode. Can you check the waveform at the inductor to check if it is in PWM mode with high current.
compare with the datasheet curves.
Can you force PWM operation?
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Re: Boost converter voltage drop
« Reply #8 on: January 27, 2020, 10:28:06 am »
can you make the MODE pin high and check?
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Offline fedimakniTopic starter

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Re: Boost converter voltage drop
« Reply #9 on: January 27, 2020, 10:39:15 am »
the traces are 10mil i think they are enough for 200mA.
you mean checking the waveform between both pin of the inductor? or one pin and the other oscilloscope probe pin to the ground?
For the TPS61291 there's no mention of pwm :/
 


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