Diode reverse current

Discussion in 'The Projects Forum' started by rakeshm55, Apr 13, 2012.

  1. rakeshm55

    Thread Starter Member

    Oct 19, 2010
    In one of the project I am working I am having two source of power one from a wall wart 5V and other a single Li ion Battery. I am using power ORing using PMEG3020EP schottky Diodes for automatic switch over of source.

    The Li ion battery is also connected to a Single cell Battery charger a
    XC6802 a Torex chip with input from the wall wart 5V.
    When the battery is unconnected the chip periodically Pulses its output at an interval of 2.5ms as an attempt to charge the Li battery which is not present. In order to avoid this pulsing I have implemented N channel switch (Q4) which will disable charging when battery not present.
    Please refer to the schematics attached.

    Now The switch (Q4) is always on whether the battery is connected or not . This is mainly due to the reverse current of PMEG3020EP which is of the order of 0.2mA @ 5V reverse. Due to which I can observe the pulsing even when battery is disconnected. How can i solve this problem in the current setup. Is there a work around ,What if I replace R33 with a diode.

    PLease help.
    Rakesh M.

  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
    I read the diode datasheet as Irev=30uA typical at 5V and 25°C. See Fig. 2.
  3. rakeshm55

    Thread Starter Member

    Oct 19, 2010

    THe value of 0.2mA @ 5V was current I observed when connected VBAT pin to ground.