ICS1722
QuickSaver® Charge Controller for Nickel-Cadmium
and Nickel-Metal Hydride Batteries
General Description
The
ICS1722
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 termination. The
ICS1722
employs a four stage charge sequence that provides a complete
recharge without overcharging. The controller has nine user-
selectable charge rates and six user-selectable auxiliary modes
available for customized charging systems.
The
ICS1722
monitors for the presence of a battery and begins
charging when a battery is installed. The
ICS1722
is for
applications where temperature sensing is not required by the
charge controller.
Features
•
•
Charge termination methods include:
-
Voltage slope
-
Charge timers
Four stage charge sequence:
-
Soft start charge
-
Fast charge
-
Topping charge
-
Maintenance charge
Reverse-pulse charging available in all charge stages
Nine programmable charge rates between 15 minutes (4C)
and four hours (C/4)
Continuous polling mode for battery detection
Six auxiliary modes include:
-
Discharge-before-charge
-
Ten hour C/10 conditioning charge
-
Direct to C/40 maintenance charge
-
Charging system test provided through controller
Adjustable open circuit (no battery) voltage reference
Applications
Battery charging systems for:
- Portable consumer electronics
- Power tools
- Audio/video equipment
- Communications equipment
•
•
•
•
•
•
Block Diagram
RESET
OPEN CIRCUIT
REFERENCE
0.5V
VOLTAGE
SENSE
MODE SELECT
CHARGE
SELECT
RC
RAM
ROM
OUTPUT
CONTROL
MICROCODE CONTROL
POLLING
MODE LED
CHARGE
MODE LED
ADC
PROCESSOR
MAINTENANCE
MODE LED
CHARGE
CONTROL
DISCHARGE
CONTROL
OSCILLATOR
ICS1722
Pin Configuration
CHG
DCHG
PFN
MMN
CMN
SEL0
VSS
SEL1
1
2
3
4
5
6
7
8
16-Pin DIP or SOIC
16
15
14
VDD
unused
VIN
OPREF
AUX1
AUX0
RC
MRN
ICS1722
13
12
11
10
9
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
MMN
CMN
SEL0
VSS
SEL1
MRN
RC
AUX0
AUX1
OPREF
VIN
unused
VDD
Type
OUT
OUT
OUT
OUT
OUT
IN
IN
IN
IN
IN
IN
IN
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 detect indicator. An active low turns on an external indicator to show the controller is polling for
the presence of the battery.
Maintenance mode indicator. An active low turns on an external indicator showing the battery is either in
the topping charge, maintenance charge or auxiliary condition mode. The indicator flashes during the
auxiliary discharge mode.
Charge mode indicator. An active low turns on an external indicator to show the controller is either in a
soft start charge or fast charge.
Tri-level input used with the SEL1 pin to program the device for the desired charge rate.
Ground.
Tri-level 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.
Tri-level input used with the AUX1 pin to program the device for an auxiliary operating mode.
Tri-level input used with the AUX0 pin to program the device for an auxiliary operating mode.
Open circuit (no battery) voltage reference. An external resistor divider on this pin sets the open circuit
voltage reference used to detect the presence of a battery.
Battery voltage normalized to one cell with an external resistor divider.
Ground.
Device supply =+5.0 VDC
Pins 9 and 13 have an internal pull-up.
Pins 6,8,11,12 float to 2.3V when unconnected.
2
ICS1722
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)
S oft-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
ICS1722
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
ICS1722
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
ICS1722
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
ICS1722
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
ICS1722
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 MMN indicator is activated
continuously 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
ICS1722
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, or, if the
ten hour timer mode is enabled, until the timer stops the controller.
The MMN indicator is activated continuously during this stage.
cycle
time
delay time
cycle
time
Figure 5: Representative timing diagram for topping and maintenance charge
5
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