PCM example
Li-ion batteries and battery packs are operated with protection circuit.
When using Li-Ion batteries in conditions with elevated ambient temperature it is recommended to install a thermal fuse to protect the battery from overheating. It is a standard procedure.
Main outputs of the module control chip (in the SOT23-5 package):
VDD: Charger input positive polarity.
VSS: Charger input negative polarity.
DO: Battery discharge control output.
Protection circuit disconnects the gate of the field-effect transistor through which the discharge current flows at a battery voltage value of 2,300 +\-0.080V and connects it at a battery voltage value of 4,275+\-0.025V.
CO: Battery charge control output.
Protection circuit disconnects the gate of the field-effect transistor through which the charge current flows at a battery voltage value of 4,275+\-0.025V and connects it at a battery voltage value of 2,300+\-0.080V.
VM: Voltage monitoring input (between VM and VSS contacts).
Protection circuit controls the battery discharge current by the voltage drop on the key elements: field-effect transistors (REF).
List of module states.
Normal (operating) condition.
During battery operation protection circuit module takes readings of voltage and current from the VDD (+) and VSS (-) connection terminals, controlling the charge and discharge process. If the battery voltage level is higher than VDL:2,300+/-0.080V (minimum discharge voltage) and lower than VCU:4,275+/-0.025V (maximum charge voltage), the circuit includes both field-effect transistors (REF), allowing the battery charger to conduct a charge or discharge cycle.
Upper charge limit. (Charge cycle.)
When the battery voltage begins to increase in comparison with the VCU voltage 4,275+/-0.025V (maximum charge voltage), protection scheme stops charging and applying the voltage to the gate of the corresponding field-effect transistor (REF) that connects the charge circuit. When the voltage is reduced to the VC level: 4.175 +/-0.050V (normal charge voltage), protection circuit supplies voltage to the gates of both field-effect transistors, turning them on.
Lower discharge limit. (Discharge cycle.)
When the battery voltage begins to decrease in comparison with the VDL voltage 2,300 +/-0.080V (maximum discharge voltage), protection scheme stops discharging and applying voltage to the gate of the corresponding field-effect transistor (REF) that connects the discharge circuit. When the voltage is increased to the VDU level: 2,400 +/-0,100V (normal discharge voltage), protection circuit supplies voltage to the gates of both field-effect transistors, turning them on.
Discharge current control.
Discharge current of the battery is determined by measuring the voltage drop on the key elements – field-effect transistors.
When the voltage drops on the key elements, and module determines it when VM input reaches less than VIOV: 0.100+/-0.300V, it stops the discharge by turning off the corresponding element (REF). The circuit goes into a normal state when the active resistance between the contacts EB+ and EB- is more than 500 mOhm.
Time characteristics of the scheme.
Cut-off time for maximum charge voltage - 2.0C max
Cut-off time for the minimum discharge voltage - 250 msec
Maximum charge voltage cut-off time 2.0 (max)
Cut-off time for exceeding the permissible current - 16 msec
Values of cut-off voltages.
VCU (maximum charge voltage) - 4,275 +/- 0,025V
VCL (normal charge voltage) - 4,175 +/- 0,050V
VDL (minimum discharge voltage) - 2,300 +/- 0,080V
VDU (normal discharge voltage) - 2,400 +/- 0,100V
VIOV (Exceeding the permissible current) - 0,100 +/- 0,030V
Current consumption.
Operating current — 3.0 mA
Standby current — 0.1 mA
Similar protection schemes are used also for battery packs to protect two or more cells series connected. And the state control of the whole battery includes monitoring of each battery cell separately.
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