Extended Power Management


Thread Starter


Dear All,

Could anybody explain to me the details of Extended Power Management
Scheme? Or could anybody suggest any good link for all the details on
tolerances of 1.2V and 1.8 V supply rails on PCBAs?

Extended Power Management Scheme is normally found in a System On Chip
solutions using low drop series pass transistors for 1.8 V and 1.2 V
supply rails.

Here is the reason why I would like to know in every details of it:

I am now working on power up testing of a typical PCBA by using Bed of
Nails style test fixture.

In one typical testing scheme, I have to measure 1.2V and 1.8V power

The Manufacture Specified that the voltage measurement on 1.2V and
1.8V in given Golden PCBA should not exceed 1.26 V and 1.89 V

I could verify that by supplying power directly to the PCBA and
measuring the rails by Agilent DMM 34401A. I measured more than 10

However, after putting the PCBAs onto the Bed of Nail style test
fixture, I found that the measurements are exceeding the limits quite

For 9 out of 10 times. 1.8 V rail measures 1.891 ~ 1.894. For 6 out of
10 times 1.2V rail measures 1.260025 to 1.272.

Checking the PCBA schematics, I found that 1.2V and 1.8V rails are
controlled by extended power management part of the main processor

It looks like a Linear Voltage Control scheme. 10V adaptor supply is
converted to 3.3V by a DC to DC converter. This 3.3V is passing
through a low drop series pass transistor (controlled by core
processing IC) to give the output of 1.8V. This 1.8V is passing
through another low drop series pass transistor to give the output

I am checking on the PCBA and Test System now to find the root cause
of it.

Thanks and Best Regards