bq24075 not working without battery

Atmeg

Other Parts Discussed in Thread: BQ24075

I'm using bq24075 with typical schematic from DS, SYSOFF, CE, EN1 tied to GND, EN2 to OUT.

47k on TMR, 750E on ILIM, 2.2k on ISET, 10k on TS. 4.4V on IN.

When battery is connected everything is ok, but when no battery connected and only external voltage on IN is applied, bq24075 is not started and no voltage is on OUT pin.

If I connect the battery, then connect external voltage, it starts, and I can disconnect the battery and the system is running. But It need to able to run without battery too.

over 9 years ago

0 Michael Allwright over 9 years ago

Prodigy 240 points

You'll need to post up your schematic, just stating that you are using the typical schematic isn't nearly enough to provide any help.

What is your external voltage source, USB? Adapter? what is the input current? and what sort of load have you connected to the output of the BQ24075?

0 Atmeg over 9 years ago in reply to Michael Allwright

Intellectual 870 points

schematic:

Load current at startup is about 20 mA

Input source is 2A step down

0 Atmeg over 9 years ago in reply to Atmeg

Intellectual 870 points

atic :(

0 Jeff F over 9 years ago in reply to Atmeg

TI__Guru*** 143950 points

This device as the VINDPM feature which monitors the input voltage and reduces the input current limit if the input voltage drops below a certain level in order to prevent total collapse of the input source. Your input voltage is below the 4.5V typical threshold and so the input current allowed has been automatically reduce to 0A.

You will need a higher input voltage in order for the IC to operate normally.

0 Jeff F over 9 years ago in reply to Jeff F

TI__Guru*** 143950 points

VINDPM is only active when EN2=0. Since your EN2 is tied to OUT, it is initially low and I think that is what is causing the problem. To test my theory, can you connect EN2 high (to VIN for example) and see if you get an output voltage.

Please note that even if you disable VINDPM, your output voltage and charge current will be reduced by IC's the dropout voltage of VDO(IN-OUT) = 300mV typical.

0 Atmeg over 9 years ago in reply to Jeff F

Intellectual 870 points

I increase the input voltage above 4.5V but nothing changes.

Then I pull EN2 to VIN by 10k, it works now.. It turned out a good idea to place R52 here)

Thank you.

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bq24075 not working without battery