Re: Garmin eMap: Dead?
- From: miso@xxxxxxxxx
- Date: 13 Apr 2005 13:50:20 -0700
Nothing I stated doesn't have good science behind it.
Consider shorting the battery terminals. As you know since you seem to
be an expert, all CMOS chips on bulk or epi (i.e. exclude SOI) have
reverse biased diodes on their power supply rails. If you short the
battery terminals, you pull down all the internal nodes to within a
diode of ground. Occasionally the circuit won't have such a parasitic
diode, especially in start-up circuits that use MOS caps, and you can
get the internal node charged with only leakage to pull it down. Often
this happens as the chip slides down the rail to be tested. Generally
if such nodes exist, the designer puts in a reverse biased diode to the
positive rail since the ATE's first step in testing is bring all pins
to ground. By shorting the battery terminal, you are providing a
discharge path.
I assume you understand "reverse power" since you are the expert, but
lets say you forgot how it works. Some voltage regulators can prevent
voltage from the load side from reaching the source side, i.e. reverse
power. [Situation is short or float the input of the regulator and
place a voltage at the output of the regulator.] Thus if such
regulators are used, then the power supply shorting trick doesn't work
since there is no reverse power.
Lance's big mistake was powering the GPS with weak batteries. Operating
in this mode requires faith that the engineers designed a decent
undervoltage lockout circuit. I've run into chips that fry if operated
from a low voltage (mostly my own chips designs where I screwed up). If
there are DC/DC converters in the emap, it is possible one got damaged
if operated at a funny voltage.
Many consumer goods are designed such that an internal ADC handles the
undervoltage lockout. This works fine if the situation is you start
from a high voltage (fresh batteries) and then drain the batteries.
This is because the device shuts down before the battery voltage is too
low. To handle undervoltage lockout from the opposite direction, i.e.
starting from zero and then going to a low voltage, is a more difficult
design. Generally this had to be done with analog circuits, i.e power
supply supervisory chips.
I haven't seen modern chip caps suffer from a lack of voltage. This was
really common in old electronics gear, but the technology is different.
The chip caps are very sensitive to overvoltage, though that shouldn't
have happened in this situation.
.
- Follow-Ups:
- Re: Garmin eMap: Dead?
- From: Peter
- Re: Garmin eMap: Dead?
- References:
- Garmin eMap: Dead?
- From: Lance
- Re: Garmin eMap: Dead?
- From: Hans-Georg Michna
- Garmin eMap: Dead?
- Prev by Date: Re: smallest possible GPS device
- Next by Date: Re: [OT] WWVB Time service
- Previous by thread: Re: Garmin eMap: Dead?
- Next by thread: Re: Garmin eMap: Dead?
- Index(es):
Relevant Pages
|
