rgbphil
03-25-2007, 11:51
Hi,
I'm trying to design an external charger for Razr batteries (BR-50 I think).
I've located a chip, the Microchip MCP73863 which seems suitable and simple with all the appropriate charging methods built in.
See http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1335&dDocName=en024022
for datasheet of this chip.
This chip also requires that the thermal monitoring thermistor on the battery be connected to determine the hot/cold cut-off points when charging. Typically the thermistor is connected to a voltage divider and the voltage monitored. If the battery is too cold or too hot during charging, then the charge current is shut off for safety.
Does anyone know the temperature/resistance characteristics of the Razr battery thermistor, the part/manufacturer of the thermistor or any other details to help design a circuit using this (or similiar) chips? Even the cut off voltages monitored by the circuit would be helpful as I can work backwards from that.
I've looked in the schematics for the Razr but the thermal monitoring circuit simply goes into a large ASIC....so who knows what levels that is using, although the circuit shows the same sort of voltage divider network as the Microchip MCP73863.
Also any pointers to Nokia type batteries would be helpful as well.
Thanks
Phil
I'm trying to design an external charger for Razr batteries (BR-50 I think).
I've located a chip, the Microchip MCP73863 which seems suitable and simple with all the appropriate charging methods built in.
See http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1335&dDocName=en024022
for datasheet of this chip.
This chip also requires that the thermal monitoring thermistor on the battery be connected to determine the hot/cold cut-off points when charging. Typically the thermistor is connected to a voltage divider and the voltage monitored. If the battery is too cold or too hot during charging, then the charge current is shut off for safety.
Does anyone know the temperature/resistance characteristics of the Razr battery thermistor, the part/manufacturer of the thermistor or any other details to help design a circuit using this (or similiar) chips? Even the cut off voltages monitored by the circuit would be helpful as I can work backwards from that.
I've looked in the schematics for the Razr but the thermal monitoring circuit simply goes into a large ASIC....so who knows what levels that is using, although the circuit shows the same sort of voltage divider network as the Microchip MCP73863.
Also any pointers to Nokia type batteries would be helpful as well.
Thanks
Phil