EUP8202-4.2/8.4
pin changes to a high impedance state and the 390k
resistor will then pull the pin high to indicate charging
has stopped.
CHRG Status Output Pin
When a charge cycle starts, the
pin is pulled to
CHRG
ground by an internal N-channel MOSFET which is
capable of driving an LED. When the charge current
drops below the End-of-Charge threshold for more than
120µs, the N-channel MOSFET turns off and a weak
25µA current source to ground is connected to the
Gate Drive
The EUP8202gate driver can provide high transient
currents to drive the external pass transistor. The rise and
fall times are typically 20ns and 50ns respectively when
driving a 2000pF load, which is typical for a P-channel
MOSFET with RDS(ON) in the range of 50mΩ.
A voltage clamp is added to limit the gate drive to 8V
below VCC. For example, if VCC is 10V then the GATE
output will pull down to 2V max. This allows low
voltage P-channel MOSFETs with superior RDS(ON) to be
used as the pass transistor thus increasing efficiency.
pin. This weak 25µA pull-down remains until
CHRG
the timer ends the charge cycle, or the charger is in
manual shutdown or sleep mode.
Table1:
Status Pin Summary
CHRG
CHARGE STATE
Pin
CHRG
Trickle Charge in Process
Constant Current Charge in Process
Constant Voltage Charge in Process
Strong On
Strong On
Strong On
Strong On
(remains the
same)
Hi-Z
Hi-Z
Weak On
Weak On
Stability
Both the current loop and the voltage loop share a
common, high impedance, compensation node (COMP
pin). A series capacitor and resistor on this pin
compensates both loops. The resistor is included to
provide a zero in the loop response and boost the phase
margin. The compensation capacitor also provides a
soft-start function for the charger. Upon start-up, then
ramp at a rate set by the internal 100µA pullup current
source and the external capacitor. Battery charge current
starts ramping up when the COMP pin voltage reaches
0.85V and full current is achieved with the COMP pin at
1.3V. With a 2.2µF capacitor, time to reach full charge
current is about 10ms. Capacitance can be increased if a
longer start-up time is needed.
Charge Suspend (Temperature)
Timer Fault
Sleep / Shutdown
End of Charge
Battery Disconnected
After a time out occurs (charge cycle ends), the pin will
become high impedance. By using two different value
resistors, a microprocessor can detect three states from
this pin (charging, end-of-charge and charging stopped)
see Figure 6.
Automatic Battery Recharge
After the 3 hour charge cycle is completed and both the
battery and the input power supply (wall adapter) are still
connected, a new charge cycle will begin if the battery
voltage drops below 4.05V per cell due to self-discharge
or external loading. This will keep the battery capacity at
more than 80% at all times without manually restarting
the charge cycle.
Battery Temperature Detection
A negative temperature coefficient (NTC) thermistor
located close to the battery pack can be used to monitor
battery temperature and will not allow charging unless
the battery temperature is within an acceptable range.
Connect a 10kΩ thermistor from the NTC pin to ground.
If the temperature rises to 50°C, the resistance of the
NTC will be approximately 4.2kΩ. With the 85µA
pull-up current source, the Hot temperature voltage
threshold is 360mV. For Cold temperature, the voltage
threshold is set at 2.4V which is equal to 0°C (RNTC ≅
28kΩ) with 85µA of pull-up current. If the temperature is
outside the window, the GATE pin will be pulled up to
VCC and the timer frozen while the output status at the
Figure 6. Microprocessor Interface
To detect the charge mode, force the digital output pin,
OUT, high and measure the voltage at the
pin.
CHRG
The N-channel MOSFET will pull the pin low even with
a 2k pull-up resistor. Once the charge current drops
below the End-of-Charge threshold, the N-channel
MOSFET is turned off and a 25µA current source is
connected to the
pin. The IN pin will then be
CHRG
pulled high by the 2k resistor connected to OUT. Now
force the OUT pin into a high impedance state, the
current source will pull the pin low through the 390k
pin remains the same. The charge cycle begins
CHRG
resistor. When the internal timer has expired, the
CHRG
or resumes once the temperature is within the acceptable
DS8202 Ver 1.1 Nov.2007
17
EUTECH [ EUTECH MICROELECTRONICS INC ]
