Table of Contents
Advertisement
2-34
Equipment Overview: Theory of Operation
The sole purpose for resistor R151 is to protect Moe's ADC (AN3) pin in the case
where the temperature signal TBATTERY becomes inadvertently tied to VBATT+.
This can easily occur since the two pins are adjacent. Should the short occur, resistor
R151 will limit the current and Moe's internal protection diodes will clamp the
voltage to +3V-C.
Battery Voltage Sensing
Moe continuously monitors battery voltage during operation. Excessively high pack
voltages during charge will cause charge termination. If battery pack voltage falls
below a predetermined threshold during operation, the battery gauge is immediately
cleared to zero and the main CPU is notified of the critically low voltage. System
software then initiates an orderly shutdown to protect the battery pack and prevent
loss of date/time.
Ambient Temperature Sensor
Extreme ambient temperatures are not favorable for battery charging. Rapid changes
in ambient temperature can cause premature or delayed charge termination by
altering the pack's temperature. Moe monitors ambient temperature via the
thermistor RT1 to ensure that charging occurs only within the "safe" temperature
range as well as to minimize the effects of changing ambient temperature on charge
termination (particularly to avoid premature termination, which would give a false
"full" reading on the gas gauge).
The battery and ambient thermistors are the same type and value to ensure
reasonable tracking. Capacitors C155 and C156 filter noise from the temperature
sense lines.
Thermistor Bias Switch
To reduce quiescent power consumption when the system is turned off, a switch
disables bias current to the battery and ambient thermistors. Q104, under control of
MOE, switches the low side of the thermistor bias networks.
Charge Light
Moe provides power to the amber charge light in the power supply compartment.
Moe communicates the current battery/charger state via this light. Four conditions
may be indicated:
1.
Battery charged (light is off)
2.
Battery needs charge (light blinks twice per second)
3.
Battery is critically low (light blinks once per second)
4.
Battery is charging (light on continuously)
NOTE
If the battery is so completely discharged that the MAX782 VL output
(+5V) falls out of regulation, the charge light will remain off.
The charge LED is contained in the power supply compartment and is disconnected
from the CPU board when the cover is open. When the cover is closed electrical
connections are re-established through the self-aligning connector. As the
connections are made in random order, there is a possibility that the VPS and
XChargeLED drive lines can connect before the power supply ground. This places a
high potential across the LED drive circuit as the power supply attempts to return its
output current through the LED. To prevent damage to the LED and driver, it is
implemented as a constant current source with a large compliance voltage. Q108
MAC 5500 resting ECG analysis system
2020299-020
Revision E
Advertisement
Table of Contents
