Datasheet

Chapter 2 — Theory of Operation
28 PB42 Portable Receipt Printer Service Manual
Charging initiation is automatic. When the print controller is disabled and
external power is applied, either from the DC jack or the external charging
contacts, the charging circuit is activated.
Each charging IC has two charging status outputs: CHARGING_[A,B]*
and CHG_DONE_[A,B]*. These outputs behave according to the
following table.
Generally, when the charger is charging CHARGING_[A,B]* is asserted,
and when charging is complete CHG_DONE_[A,B]* is asserted. Software
should be written to detect fault conditions based on the charger outputs.
CHARGING_A*, CHG_DONE_A*, CHARGING_B*, and
CHG_DONE_A* can be read on the input shift register bits 7, 6, 5, and 4,
respectively. See “Input/Output Shift Registers” on page 14 for details on
how to read the shift register.
Reading Battery Voltages
Batteries A and B are connected to channels 5 and 6 of the ADC,
respectively. See “Analog to Digital Converter” on page 16 for details on
reading data from the ADC.
The battery voltages are divided down so that a full battery corresponds to
0xff. To convert the ADC output to the actual battery voltage, multiply by
0.0343.
The battery voltages should be periodically monitored to detect the
presence of a battery, and to report low battery capacity. Due to loading
effects, the battery voltage can temporarily droop while printing. Because of
this, software should use the average of several readings when comparing
with the low battery threshold.
The LBO* interrupt generated from the 3.3 V DC-DC converter occurs
when VBB, the diode “or” of the battery voltages, falls below 5.75 V.
Behavior of IC Outputs
Charge State CHARGING_[A,B]* CHG_DONE_[A,B]*
Precharge Low High
Fast charge Low High
Fault 1 Hz, 50% duty cycle High
Charging done (>90%) High Low
Sleep mode High High
Thermistor invalid High High
Thermal shutdown High High
Battery absent High High