I am using the LT3652 charger chip,datasheet. Now, there is a status pin /CHRG. The pin is -

CHRG (Pin 4): Open-Collector Charger Status Output; typically pulled up through a resistor to a reference voltage. This status pin can be pulled up to voltages as high as VIN when disabled, and can sink currents up to 10mA when enabled. During a battery charging cycle, if required charge current is greater than 1/10 of the programmed maximum current (C/10), CHRG is pulled low. A temperature fault also causes this pin to be pulled low. After C/10 charge termination or, if the internal timer is used for termination and charge current is less than C/10, the CHRG pin remains high-impedance.

Now, an application circuit is as shown below -

application circuit

Now, it says that the /CHRG pin can sink in a max of 10mAmps and it shows an LED connected to show status. Most SMD LEDs need approx 10mAmps at least to make it turn on. I cannot supply 10mAmps as thats the maximum. So, what practical use could it serve ?


Most SMD LEDs need approx 10mAmps at least to make it turn on

From where did you get this wisdom ? Most LEDs already start to glow a bit at 1 mA. It is not that they need 10 mA to do anything.

I cannot supply 10mAmps as thats the maximum

Uhm, that means that it can sink up to 10 mA which is enough for most LEDs. Only if you would be using very old and inefficient LEDs would 10 mA not be enough. I'm talking LEDs that are 20 years old !

If you insist on more current for your LEDs, use the charging IC's output to toggle a PNP transistor and let the transistor supply the current to the LED. Instead of a PNP you could also use a PMOS.


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