isl6252a Intersil Corporation, isl6252a Datasheet - Page 14

• Manufacturer Part Number: isl6252a
• Description: Highly Integrated Battery Charger Controller For Notebook Computers
• Manufacturer: Intersil Corporation

voltage divided by the minimum sense resistor. This can be
calculated for ISL6252A with Equation 7:
I
Maximum charge current can be calculated for ISL6252 with
Equation 8:
I
With CHLIM = 0.7V and R
I
Setting the Input Current Limit
The total input current from an AC adapter, or other DC
source, is a function of the system supply current and the
battery-charging current. The input current regulator limits
the input current by reducing the charging current, when the
input current exceeds the input current limit set point.
System current normally fluctuates as portions of the system
are powered up or down. Without input current regulation,
the source must be able to supply the maximum system
current and the maximum charger input current
simultaneously. By using the input current limiter, the current
capability of the AC adapter can be lowered, reducing
system cost.
The ISL6252 limits the battery charge current when the input
current-limit threshold is exceeded, ensuring the battery
charger does not load down the AC adapter voltage. This
constant input current regulation allows the adapter to fully
power the system and prevent the AC adapter from
overloading and crashing the system bus.
An internal amplifier gm3 compares the voltage between
CSIP and CSIN to the input current limit threshold voltage
set by ACLIM. Connect ACLIM to REF, Float and GND for
the full-scale input current limit threshold voltage of 100mV,
75mV and 50mV, respectively, or use a resistor divider from
VREF to ground to set the input current limit as Equation 10:
An external resistor divider from VREF sets the voltage at
ACLIM according to Equation 11:
I
I
I
V
CHG MAX
CHG MIN
CHG MAX
CHG MIN
CHG MAX
CHG MIN
I
INPUT
ACLIM
,
,
,
,
,
,
=
=
=
=
=
=
=
=
VREF
------ -
R
1
(
(
2
(
(
(
(
CHLIM 49.72 2.4
CHLIM 50 5
1.5V 49.72 2.4
CHLIM 50.28
CHLIM 50
1.5V 50.28
⋅
ISL6252
⎛
⎝
ISL6252A
---------------- - V
VREF
0.05
⋅
•
⎛
⎜
⎝
•
----------------------------------------------------------------------------------------------------------------------- -
R
ISL6252A
•
•
top ACLIM
•
•
⋅
,
–
ACLIM
+
–
+
1
5
2.4
–
) R
= 0.02Ω, 1%:
+
) R
⁄
14
⁄
2.4
) 0.0202
R
) 0.0198
||
⁄
1MAX
⁄
+
bot ACLIM
1MIN
) R
152kΩ
) R
0.05
⁄
⁄
,
1MAX
1MIN
⎞
⎠
=
=
+
3573mA
R
3930mA
||
bot ACLIM
152kΩ
,
ISL6252, ISL6252A
||
(EQ. 10)
(EQ. 11)
(EQ. 7)
(EQ. 8)
152kΩ
(EQ. 9)
⎞
⎟
⎠
where R
ACLIM.
To minimize accuracy loss due to interaction with ACLIM's
internal resistor divider, ensure the AC resistance looking
back into the resistor divider is less than 25k.
When choosing the current sense resistor, note that the
voltage drop across this resistor causes further power
dissipation, reducing efficiency. The AC adapter current
sense accuracy is very important. Use a 1% tolerance
current-sense resistor. The highest accuracy of ±3% is
achieved with 100mV current-sense threshold voltage for
ACLIM = VREF, but it has the highest power dissipation. For
example, it has 400mW power dissipation for rated 4A AC
adapter and 1Ω sensing resistor may have to be used. ±4%
and ±6% accuracy can be achieved with 75mV and 50mV
current-sense threshold voltage for ACLIM = Floating and
ACLIM = GND, respectively.
A low pass filter is suggested to eliminate the switching
noise. Connect the resistor to CSIN pin instead of CSIP pin
because CSIN pin has lower bias current and less influence
on the current-sense accuracy.
AC Adapter Detection
Connect the AC adapter voltage through a resistor divider to
ACSET to detect when AC power is available, as shown in
Figure 2. ACPRN is an open-drain output and is high when
ACSET is less than V
above V
and Equation 13:
where:
• I
• V
The hysteresis is I
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 14:
where I
ICM has ±3% accuracy. It is recommended to have an RC
filter at the ICM output for minimizing the switching noise.
V
V
ICM
th rise
th fall
hys
,
,
ACSET
=
is the ACSET input bias current hysteresis, and
INPUT
19.9 I
=
th,fall
=
bot_ACLIM
⎛
⎜
⎝
⎛
⎜
⎝
R
------ -
R
= 1.24V (min), 1.26V (typ) and 1.28V (max).
R
------ -
R
•
8
9
. V
8
9
+
INPUT
is the DC current drawn from the AC adapter.
+
1
th,rise
1
⎞
⎟
⎠
⎞
⎟
⎠
⋅
hys
⋅
V
and R
V
•
ACSET
ACSET
R
th,rise
R
and V
8
2
, where I
top_ACLIM
, and active low when ACSET is
–
th,fall
I
hys
hys
⋅
are given by Equation 12
R
8
are external resistors at
= 2.2µA (min),
July 19, 2007
(EQ. 14)
(EQ. 13)
(EQ. 12)
FN6498.1