ISL6256 Datasheet, PDF (16/26 Pages) Intersil Corporation – Highly Integrated Battery Charger with Automatic Power Source Selector for Notebook Computers

ISL6256, ISL6256A
V_{th, rise}
=
⎛
⎜
⎝
R_-----8-
R₉
+
⎞
1⎟
⎠
⋅ V_ACSET
V_{th, fall}
=
⎛
⎜
⎝
R_-----8-
R₉
+
⎞
1⎟
⎠
⋅ V_ACSET – I_hys ⋅ R₈
(EQ. 12)
(EQ. 13)
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 3. 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 Equations 14 and 15:
V_{th, rise}
=
⎛
⎜
⎝
R_-----1---4-
R₁₅
+
⎞
1⎟
⎠
• V_DCSET
(EQ. 14)
V_{th, fall}
=
⎛
⎜
⎝
R_-----1---4-
R₁₅
+
⎞
1⎟
⎠
• V_DCSET – I_hysR₁₄
(EQ. 15)
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_hys R₁₄, 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 0V to 2.5V. The
voltage of ICM is proportional to the voltage drop across
CSIP and CSIN, and is given by Equation 16:
ICM = 19.9 • I_INPUT • R₂
(EQ. 16)
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 2. VDDP connects
to VDD through an external low pass filter. Bypass VDDP
and VDD with a 1µF capacitor.
Shutdown
The ISL6256 features a low-power shutdown mode. Driving
EN low shuts down the ISL6256. 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 ISL6256 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 ISL6256 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 8mV, 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 3mV, 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 and the P-Channel MOSFET controlled by
SGATE is allowed to turn on when the adapter current is high
enough. If it is greater, then the P-Channel MOSFET controlled
by SGATE turns off and BGATE turns on the battery discharge
P-Channel MOSFET to minimize the power loss. Also, the
charging function is disabled. 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 3) is turned off which keeps the battery
from supplying the system bus. The comparator looking at
CSON and DCIN has 300mV of hysteresis to avoid chattering.
Only 2S and 3S are supported for DC aircraft power
applications. For 4S battery packs, set DCSET = 0.
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 +125°C, charging will start-up again.
16
FN6499.3
September 14, 2010