Can the LP2980-ADJ be used as a current source set to 1.5ma by leaving the ADJ open and connecting it to the output pin with a 820 resistor.
Device would charge a battery. Regulator would be turn off when the battery reached 3.5V.
Vin would be 5V
Hi Les,
The internal reference of the LP2980-ADJ is tied to RTN of the linear regulator.
So connecting the adjust pin to Vout through a resistor will not generate the current source you are looking for.
If you wish to use this technique, you need a floating reference based LDO.
The LM317 datasheet has this type of floating reference, and shows a good example of a current source in the application section.
I've copied a snapshot of this section below.
Alternatively you can connect your LP2980-ADJ LDO in the following way to give you a current source.
The con of using this technique is the floating GND of the input source and LDO with respect to the load.
A third option is to use a dedicated current source IC.
The LM334 is an option you may wish to consider.
Thanks,
- Stephen
Hi Les,
The image of the second option did not go through for some reason.
I've attached the schematic below.
Thanks,
- Stephen
