In this mode, charging is stopped, the battery charger does not require a reset to resume normal operation.
11.2
Battery Charger Trimming and Calibration
The battery charger default trim values are written by CSR into internal ROM when each IC is characterised. CSR
provides various PS Keys for overriding the default trims, see Section 11.4.
11.3
VM Battery Charger Control
The VM charger code has overall supervisory control of the battery charger and is responsible for:
■
Responding to charger power connection/disconnection events
■
Monitoring the temperature of the battery
■
Monitoring the temperature of the die to protect against silicon damage
■
Monitoring the time spent in the various charge states
■
Enabling/disabling the charger circuitry based on the monitored information
■
Driving the user visible charger status LED(s)
11.4
Battery Charger Firmware and PS Keys
The battery charger firmware sets up the charger hardware based on the PS Key settings and call traps from the
VM charger code. It also performs the initial analogue trimming. Settings for the charger current depend on the
battery capacity and type, which are set by the user in the PS Keys.
For more information on the CSR8640 BGA, including details on setting up, calibrating, trimming and the PS Keys,
see
Lithium Polymer Battery Charger Calibration and Operation for CSR8670
application note.
11.5
External Mode
The external mode is for charging higher capacity batteries using an external pass device. The current is controlled
by sinking a varying current into the CHG_EXT pin, and the current is determined by measuring the voltage drop
across a resistor, R
sense
, connected in series with the external pass device, see Figure 11.2. The voltage drop is
determined by looking at the difference between the VBAT_SENSE and VBAT pins. The voltage drop across
R
sense
is typically 200mV. The value of the external series resistor determines the charger current. This current can
be trimmed with a PS Key.
In Figure 11.2, R1 (220mΩ) and C1 (4.7µF) form a RC snubber that is required to maintain stability across all battery
ESRs. The battery ESR must be <1.0Ω
Advance Information
This material is subject to CSR's non-disclosure agreement
© Cambridge Silicon Radio Limited 2011
Page 71 of 110
CS-209182-DSP1
CSR8640 BGA
Data Sheet
