ISL6251HRZ View Datasheet(PDF) - Renesas Electronics
Part Name
Description
Manufacturer
ISL6251HRZ Datasheet PDF : 20 Pages
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ISL6251, ISL6251A
TABLE 1. CELL NUMBER PROGRAMMING
CELLS
CELL NUMBER
VDD
4
GND
3
Float
2
Setting the Battery Charge Current Limit
The CHLIM input sets the maximum charging current. The current
set by the current sense-resistor connects between CSOP and
CSON. The full-scale differential voltage between CSOP and
CSON is 165mV for CHLIM = 3.3V, so the maximum charging
current is 4.125A for a 40m sensing resistor. Other battery
charge current-sense threshold values can be set by connecting a
resistor divider from VREF or 3.3V to ground, or by connecting a
low impedance voltage source like a D/A converter in the
micro-controller. Unlike VADJ and ACLIM, CHLIM does not have an
internal resistor divider network. The charge current limit
threshold is given by Equation 3:
ICHG
=
1----6---5----m-----V--- -V----C----H----L---I--M---
R1 3.3V
(EQ. 3)
To set the trickle charge current for the dumb charger, a resistor
in series with a switch Q3 (Figure 12) controlled by the micro-
controller is connected from CHLIM pin to ground. The trickle
charge current is determined by Equation 4:
ICHG
=
1----6---5----m-----V--- -V----C----H----L---I--M-----,-t--r--i--c---k---l--e-
R1
3.3 V
(EQ. 4)
When the CHLIM voltage is below 88mV (typical), it will disable
the battery charger. When choosing the current sensing resistor,
note that the voltage drop across the sensing resistor causes
further power dissipation, reducing efficiency. However, adjusting
CHLIM voltage to reduce the voltage across the current sense
resistor R1 will degrade accuracy due to the smaller signal to the
input of the current sense amplifier. There is a trade-off between
accuracy and power dissipation. A low pass filter is
recommended to eliminate switching noise. Connect the resistor
to the CSOP pin instead of the CSON pin, as the CSOP pin has
lower bias current and less influence on current-sense accuracy
and voltage regulation accuracy.
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 ISL6251, ISL6251A 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 shown in Equation 5:
IINPUT
1
R2
0.05
VREF
VACLIM
0.050
(EQ. 5)
An external resistor divider from VREF sets the voltage at ACLIM
according to Equation 6:
VACLIM
=
V
REF
--------------------------R-----b---o----t-_---A----C----L---I-M----------1---5----2---k----------------------------
Rtop_ACLIM 152k + Rbot_ACLIM 152k
(EQ. 6)
where Rbot_ACLIM and Rtop_ACLIM are external resistors at
ACLIM. To minimize accuracy loss due to interaction with ACLIM’s
internal resistor divider, ensure the AC resistance looking back into
the external 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 1W 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 12. ACPRN is an open-drain output and is high when
ACSET is less than Vth,rise, and active low when ACSET is above
Vth,fall. Vth,rise and Vth,fall are given by Equations 7 and 8:
Vth,rise
R8
R9
1 VACSET
(EQ. 7)
Vth,fall
R8
R9
1 VACSET
IhysR8
(EQ. 8)
Where Ihys is the ACSET input bias current hysteresis and VACSET
= 1.24V (min), 1.26V (typ) and 1.28V (max). The hysteresis is
IhysR8, where Ihys = 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
FN9202 Rev 3.00
March 13, 2014
Page 13 of 20
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