ICS1712
QuickSaver® Charge Controller for Nickel-Cadmium
and Nickel-Metal Hydride Batteries
General Description
The
ICS1712
is a CMOS device designed for the intelligent charge
control of either nickel-cadmium (NiCd) or nickel-metal-hydride
(NiMH) batteries. The controller uses a pulsed-current charging
technique together with voltage slope and/or temperature slope
termination. The
ICS1712
employs a four stage charge sequence
that provides a complete recharge without overcharging. The
controller has four user-selectable charge rates available for
customized charging systems.
The
ICS1712
monitors for the presence of a battery and begins
charging if a battery is installed within the first 10 seconds after a
reset. Voltage and temperature are measured to ensure a battery is
within fast charge conditions before charge is initiated.
Features
•
Multiple charge termination methods include:
-
Voltage slope
-
Temperature slope
-
Maximum temperature
-
Charge timer
Four stage charge sequence:
-
Soft start charge
-
Fast charge
-
Topping charge
-
Maintenance charge
Reverse-pulse charging available in all charge stages
Four programmable charge rates between 15 minutes (4C) and
two hours (C/2)
Out-of-temperature range detection
-
Hot battery: charger shutdown
-
Cold battery: low current charge
Ten second polling mode for battery detection
Battery fault with shutdown protection
•
•
•
•
•
•
Applications
Battery charging systems for:
-
Portable consumer electronics
-
Power tools
-
Audio/video equipment
-
Communications equipment
-
Wireless handsets
Block Diagram
CHARGE
SELECT
2.0V
0.5V
VOLTAGE
SENSE
TERMINATION
SELECT
TEMPERATURE
SENSE
HOT
RESET
RC
OSCILLATOR
QuickSaver
®
is a registered trademark of Galaxy Power, Inc.
POLLING/
FAULT LED
MICROCODE CONTROL
CHARGE
MODE LED
OUTPUT
CONTROL
TEMPERATURE
STATUS LED
CHARGE
CONTROL
RAM
ROM
DISCHARGE
CONTROL
ADC
PROCESSOR
COLD
ICS1712
Pin Configuration
1
2
3
4
5
6
7
8
16
15
14
CHG
DCHG
PFN
CMN
OTN
SEL0
VSS
AVSS
VDD
unused
VIN
THERM
DTSEL
RC
MRN
SEL1
ICS1712
13
12
11
10
9
16-Pin DIP or SOIC
Pin Definitions
Pin
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Note:
Pin Name
CHG
DCHG
PFN
CMN
OTN
SEL0
VSS
AVSS
SEL1
MRN
RC
DTSEL
THERM
VIN
unused
VDD
Type
OUT
OUT
OUT
OUT
OUT
IN
Definition
Active high TTL compatible signal used to turn on an external current source to provide current to
charge the battery.
Active high TTL compatible signal available to turn on a discharge circuit.
Polling fault indicator. An active low turns on an external indicator to show the controller is either
polling for the presence of the battery or has determined the battery has been removed.
Charge mode indicator. A continuous low shows the controller is in a soft start or fast charge. The
indicator flashes during the topping and maintenance charges.
Out-of-temperature range indicator. An active low turns on an external indicator showing the battery is
out of the normal fast charge temperature range.
Input used with the SEL1 pin to program the device for the desired charge rate.
Ground.
Ground.
IN
IN
IN
IN
IN
IN
Input used with the SEL0 pin to program the device for the desired charge rate.
Master reset signal. A logic low pulse greater than 700 ms initiates a device reset.
An external resistor and capacitor sets the frequency of the internal clock.
Selects temperature slope and/or voltage slope termination
Thermistor or thermal switch input for temperature sensing.
Battery voltage normalized to one cell with an external resistor divider.
Ground.
Device supply =+5.0 VDC
Pins 6, 9, 10 and 13 have an internal pull-up.
Pin 12 has an internal pull-down.
2
ICS1712
Controller Operation
Charging Stages
The charging sequence consists of four stages. The application of
current is shown graphically in Figure 1. The soft start stage
gradually increases current levels up to the user selected fast
charge rate during the first two minutes. The soft start stage is
followed by the fast charge stage, which continues until
termination. After termination, a two hour C/10 topping charge is
applied. The topping charge is followed by a C/40 maintenance
charge.
Soft Start Charge
Some batteries may exhibit an unusual high impedance condition
while accepting the initial charging current, as shown in Figure 2.
Unless dealt with, this high impedance condition can cause a
voltage peak at the beginning of the charge cycle that would be
misinterpreted as a fully charged battery by the voltage termination
methods.
The soft start charge eases batteries into the fast charge stage by
gradually increasing the current to the selected fast charge rate. The
gradual increase in current alleviates the voltage peak. During this
stage, only positive current pulses are applied to the battery. The
duty cycle of the applied current is increased to the selected fast
charge rate, as shown in Figure 3, by extending the current pulse
on every cycle until the pulse is about one second in duration. The
initial current pulse is approximately 200ms. The CMN indicator is
activated continuously during this stage
Average
Current
(not to scale)
Soft-Start
Fast Charge
Topping Charge
Maintenance Charge
Stage 1
0
2 min
Stage 2
termination
Stage 3
termination + 2 hours
Stage 4
Time (not to scale)
Figure 1: Graphical representation of average current levels during the four charging stages
Figure 2: High impedance voltage spike at the beginning of charge
3
ICS1712
Initial Pulse
Width
Initial Pulse
Width
increment
time
Initial Pulse
Width
2 x increment
time
cycle time
cycle time
cycle time
Figure 3: Cycle-to-cycle increase of the soft-start current pulse widths
Fast Charge
In the second stage, the
ICS1712
applies the charging current in a
series of charge and discharge pulses. The technique consists of a
positive current charging pulse followed by a high current, short
duration discharge pulse. The cycle, shown with charge, discharge,
rest and data acquisition periods in Figure 4, repeats every second
until the batteries are fully charged.
The amplitude of the current pulse is determined by system
parameters such as the current capability of the charging system,
the desired charge rate, the cell capacity and the ability of that cell
to accept the charge current. The
ICS1712
can be set for nine user-
selectable fast charge rates from 15 minutes (4C) to four hours
(C/4). Charge pulses occur approximately every second. The CMN
indicator is activated continuously during this stage.
rest
time
fast charge pulse width
rest
time
voltage
acquisition time
discharge pulse width
cycle time
Figure 4: Charge cycle showing charge and discharge current pulses
4
ICS1712
The discharge current pulse amplitude is typically set to about 2.5
times the amplitude of the charging current based on 1.4V/cell. For
example, if the charge current is 4 amps, then the discharge current
is set at about 10 amps. The energy removed during the discharge
pulse is a fixed ratio to the positive charge rate. The amplitude of
the discharge pulse does not affect the operation of the part as
described in this section.
A voltage acquisition window immediately follows a brief rest time
after the discharge pulse. No charge is applied during the rest time
or during the acquisition window to allow the cell chemistry to
settle. Since no current is flowing, the measured cell voltage is not
obscured by any internal or external IR drops or distortions caused
by excess plate surface charge. The
ICS1712
makes one
continuous reading of the no-load battery voltage during the entire
acquisition window. The voltage that is measured during this
window contains less noise and is a more accurate representation
of the true state of charge of the battery.
Topping Charge
The third stage is a topping charge that applies current at a rate low
enough to prevent cell heating but high enough to ensure a full
charge.
The topping charge applies a C/10 charging current for two hours.
The current consists of the same pulse technique used during the
fast charge stage; however, the duty cycle of the pulse sequence
has been extended as shown in Figure 5. Extending the time
between charge pulses allows the same charging current used in the
fast charge stage so that no changes to the current source are
necessary. For example, the same charge pulse that occurs every
second at a 2C fast charge rate will occur every 20 seconds for a
topping charge rate of C/10. The CMN indicator flashes at a one
second rate during this stage.
Maintenance Charge
The maintenance charge is intended to offset the natural self-
discharge of NiCd or NiMH batteries by keeping the cells primed
at peak charge. After the topping charge ends, the
ICS1712
begins
this charge stage by extending the duty cycle of the applied current
pulses to a C/40 rate. The maintenance charge will last for as long
as the battery voltage is greater than 0.5V at the VIN pin. The
CMN indicator flashes at a one second rate during this stage.
cycle
time
delay time
cycle
time
Figure 5: Representative timing diagram for topping and maintenance charge
5
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