Hi,

I'm using the MCP1640 converter:
http://www.microchip.com/wwwproducts/devices.aspx?dDocName=3Den547080
to provide power supply for a device, which is powered either from 2
recharge'able Ni-MH batteries (2,4V), or from USB (5V) (both power
sources were separated via Schottky diodes).
The feedback circuit is set so, that the MCP1640 delivers 4.2V when
running form batteries.
According to the datasheet it is acceptable to provide higher input
voltage, that the regulated output voltage (Note 2 on the page 3 of
datasheet: For VIN > VOUT, VOUT will not remain in regulation.). So it
seems to be OK to power the device from USB.
The output voltage after the MCP1640 (c.a. 4.2V when using batteries,
or c.a. 4.7V when running from USB via Schottky diode) is further
stabilized at 3.3V using the linear voltage regulator LP2950.

Usually everything works fine, but in 2 cases the MCP1640 got burned
after the device was connected to the USB.
The chip was heated to a temperature sufficient to detach connected
tracks from the PCB.
The post mortem diagnosis showed, that possibly the capacitor at the
output of the MCP1640 was incorrectly soldered and got disconnected.
Has anybody experienced similar problems with MCP1640?
Is it possible, that temporary disconnection of the output capacitor
was the only reason why MCP1640 "exploded"?
What's interesting, the LP2950 regulator survived...

--=20
TIA and regards,
Wojtek
--=20
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