ISL6255 Datasheet, PDF (15/22 Pages) Intersil Corporation – Highly Integrated Battery Charger with Automatic Power Source Selector for Notebook Computers

ISL6255, ISL6255A
ACSET is less than V_th,rise, and active low when ACSET is
above V_th,fall. V_th,rise and V_th,fall are given by:
V_th,rise
=

R₈
R₉
+1_{} •V_ACSET
V_th,fall
=

R₈
R₉
+1_{} •V_ACSET
− I_hysR₈
Where I_hys is the ACSET input bias current hysteresis and
V_ACSET = 1.24V (min), 1.26V (typ.) and 1.28V (max.). The
hysteresis is I_hysR₈, where I_hys=2.2µA (min.), 3.4µA (typ.)
and 4.4µA (max.)
DC Adapter Detection
Connect the DC adapter voltage like aircraft power through a
resistor divider to DCSET to detect when DC power is
available, as shown in Figure 16. DCPRN is an open-drain
output and is high when DCSET is less than V_th,rise, and
active low when DCSET is above V_th,fall. V_th,rise and V_th,fall
are given by:
V_{th, rise}
=



R_-----1---4-
R₁₅
+

1

• V_DCSET
V_{th, fall}
=



R_-----1---4-
R₁₅
+

1

• V_DCSET – I_hysR₁₄
Where I_hys is the DCSET input bias current hysteresis and
V_DCSET=1.24V (min), 1.26V (typ.) and 1.28V (max.). The
hysteresis is I_hysR14, where I_hys=2.2µA (min.), 3.4µA (typ.)
and 4.4µA (max.)
Current Measurement
Use ICM to monitor the input current being sensed across
CSIP and CSIN. The output voltage range is 0 to 2.5V. The
voltage of ICM is proportional to the voltage drop across
CSIP and CSIN, and is given by the following equation:
ICM = 19.9 • I_INPUT • R₂
where I_INPUT is the DC current drawn from the AC adapter.
ICM has ±3% accuracy. It is recommended to have an RC
filter at the ICM output for minimizing the switching noise.
LDO Regulator
VDD provides a 5.0V supply voltage from the internal LDO
regulator from DCIN and can deliver up to 30mA of current.
The MOSFET drivers are powered by VDDP, which must be
connected to VDDP as shown in Figure 15. VDDP connects
to VDD through an external low pass filter. Bypass VDDP
and VDD with a 1µF capacitor.
Shutdown
The ISL6255, ISL6255A features a low-power shutdown
mode. Driving EN low shuts down the ISL6255, ISL6255A. In
shutdown, the DC/DC converter is disabled, and VCOMP
and ICOMP are pulled to ground. The ICM, ACPRN and
DCPRN outputs continue to function.
EN can be driven by a thermistor to allow automatic
shutdown of the ISL6255, ISL6255A when the battery pack
is hot. Often a NTC thermistor is included inside the battery
pack to measure its temperature. When connected to the
charger, the thermistor forms a voltage divider with a
resistive pull-up to the VREF. The threshold voltage of EN is
1.0V with 60mV hysteresis. The thermistor can be selected
to have a resistance vs temperature characteristic that
abruptly decreases above a critical temperature. This
arrangement automatically shuts down the ISL6255,
ISL6255A when the battery pack is above a critical
temperature.
Another method for inhibiting charging is to force CHLIM
below 85mV (Typ.).
Supply Isolation
If the voltage across the adapter sense resistor R2 is
typically greater than 8.5mV, the p-channel MOSFET
controlled by SGATE is turned on reducing the power
dissipation. If the voltage across the adapter sense resistor
R2 is less than 5.5mV, SGATE turns off the p-channel
MOSFET isolating the adapter from the system bus.
Battery Power Source Selection and Aircraft
Power Application
The battery voltage is monitored by CSON. If the battery
voltage measured on CSON is less than the adapter voltage
measured on DCIN, then the p-channel MOSFET controlled
by BGATE turns off. If it is greater, then BGATE turns on the
battery discharge p-channel MOSFET to minimize the power
loss. In the meantime, it also disables charging function and
turns off the AC adapter isolation p-channel MOSFET
controlled by SGATE. If designing for airplane power,
DCSET is tied to a resistor divider sensing the adapter
voltage. When a user is plugged into the 15V airplane supply
and the battery voltage is lower than 15V, the MOSFET
driven by BGATE (See Figure 16) is turned off and keeps the
battery from supplying the system bus. The comparator
looking at CSON and DCIN has 300mV of hysteresis to
avoid chattering. It supports only 3S and 2S for DC aircraft
power applications.
Short Circuit Protection and 0V Battery Charging
Since the battery charger will regulate the charge current to
the limit set by CHLIM, it automatically has short circuit
protection and is able to provide the charge current to wake
up an extremely discharged battery.
Over Temperature Protection
If the die temp exceeds 150°C, it stops charging. Once the
die temp drops below 1250°C, charging will start up again.
15
FN9203.1
June 17, 2005