ICS1708
QuickSaver® Charge Control IC for Nickel-Cadmium
and Nickel-Metal Hydride Batteries
General Description
The ICS1708 is a low cost 8 pin CMOS control IC for the intelligent charging of either nickel-cadmium (NiCd) or nickel-metal hydride
(NiMH) batteries. The ICS1708 uses a pulsed-current charging technique together with multiple voltage slope termination methods. The
ICS1708 employs a four stage charge sequence that provides a complete recharge without overcharging. The controller has three (3) user
selectable charge rates, user accessible clock, and two (2) charge status output pins. On power-up, the ICS1708 monitors for the presence of
a battery and begins charging. The ICS1708 is for applications where battery temperature protection is not required of the charge controller.
Applications
Embedded and charger stands for: Portable consumer products, Power tools, Audio/video products, Communications products, RC toys,
and Wireless products
Features
•
•
•
•
•
Charge termination methods include: Voltage slope (+∆V/dt and +/- peak detect), and Fast charge time out to maintenance mode
Four stage charge sequence: SoftStart conditioning, Fast charge, Topping charge, and Maintenance charge
Three (3) user selectable charge rates: 15 minutes (4C), 60 minutes (1C), 150 minutes (C/2.5)
Continuous polling mode for battery detection
Adjustable open circuit (no battery) voltage reference
Benefits -compared to other methods
•
•
•
•
Peak battery performance and extended cycle life
Improved battery efficiency and reliability
Lower internal resistance build-up
Lower capacity fade
Block Diagram
OPEN CIRCUIT
REFERENCE
VOLTAGE
MICROCODE CONTROL
FAST
CHARGE
0.5V
BATTERY
VOLTAGE
SENSE
ADC
PROCESSOR
RAM
RC (CLOCK)
ROM
OSCILLATOR
OUTPUT
CONTROL
CHARGE
COMPLETE
CURRENT
SOURCE
ICS1708
Pin Configuration
CHG
1
MMN
2
CMN
VSS
8
VDD
7
VIN
3
6
OPREF
4
5
RC
ICS1708
8-Pin DIP or SOIC
Pin Definitions
Pin
1
Name
CHG
Type
OUT
2
CMN
OUT
3
MMN
OUT
4
5
6
VSS
RC
OPREF
IN
IN
7
8
VIN
VDD
Note:
Definition
Active high (PFET), active low (NFET) 25mA max. TTL compatible signal used to turn on and off an external current source to
provide pulsed current to charge the battery.
Charge mode indicator. NFET drain rated at 40mA max. turns on an external indicator to show the controller is applying either a
SoftStart charge or fast charge.
Maintenance mode indicator. NFET drain rated at 40mA max. turns on an external indicator showing the battery is ready to use as the
topping charge or maintenance charge is applied.
Ground.
An external resistor and capacitor sets the frequency of the internal clock.
Open circuit (no battery) voltage reference. A pull down or external resistor divider from 5V sets a voltage reference on this pin used
to detect the presence of a battery.
Battery voltage normalized to one cell with an external resistor divider.
IN
Device supply =+5.0 VDC +/- 5% regulated. The ICS1708 requires 11mA max. average that includes brief 50mA peak currents.
When used, LEDs, pull-up resistors, and drivers require additional current from the +5VDC supply. An electrolytic and ceramic
capacitor between (or very close to) both VDD and VSS is recommended for bypassing.
Pin 6 has an internal pull-up.
Input and output pins have internal ESD protection diodes to VDD and VSS for 2KV protection per MIL STD 883 method 3015.7.
Controller Operation
Charging Stages
The charging sequence consists of four stages. The application of current is shown graphically in Figure 1. The SoftStart stage gradually
increases current levels up to the user selected fast charge rate during the first two minutes. The SoftStart stage is followed by the fast
charge stage, which continues until termination. After fast charge termination, a reduced duty cycle topping charge is applied, followed by
a further reduced cycle maintenance charge. After fast charge termination, the battery is charged and ready to use.
97%
18%
Fast Charge
A v e ra g e
C u r re n t
( no t t o s c a le )
S ta g e 1
0
2 m in
S t a ge 2
Topping Charge
2.5 to 20%
Maintenance Charge
0.6 to 5%
S t a ge 3
t e rm in a tion
S t ag e 4
t erm in atio n +
Tim e (n o t to s c a le)
Figure 1: Graphical representation of average current levels during the four charging stages
2
ICS1708
SoftStart Conditioning Charge
New, over-discharged, and batteries out of long term storage may exhibit an initial high impedance conditions in response to charging, as
shown in Figure 2. Unless dealt with, this high impedance condition can cause a voltage peak and -∆V condition at the beginning of the
charge cycle that can appear to be the response of an already full battery. To manage this condition, the ICS1708 applies a SoftStart
conditioning charge.
Figure 2: High impedance voltage spike at the beginning of charge
The SoftStart charge eases batteries into the fast charge stage by gradually increasing the duty cycle of the charge. The gradual increase
alleviates the voltage peak and the -∆V condition. The duty cycle of the applied current is increased to the fast charge rate, as shown in
Figure 3, by extending the current pulse on every cycle until the pulse is about 1.1 seconds in duration. The initial current pulse is
approximately 200ms. The CMN indicator is a continuous active low during the SoftStart conditioning stage.
Initial Pulse
Width
Initial Pulse
Width
Initial Pulse
Width
increment
time
cycle time
cycle time
2 x increment
time
cycle time
Figure 3: Cycle-to-cycle increase of the SoftStart current pulse widths
3
ICS1708
Fast Charge
In the second stage, the ICS1708 applies the charging current in a repetitive sequence consisting of positive current charging pulses followed
by a rest time and voltage acquisition time. The cycle, shown with charge, rest, and data acquisition periods in Figure 4, repeats every 1.1
seconds until the battery is fully charged.
rest time
voltage
a cqu isit ion tim e
fast charge pu lse w id th
cycle time
Figure 4: Charge cycle showing fast charge current pulses
The amplitude of the current pulse is determined by system parameters such as the current capability of the charging system, the desired
recharge time, battery capacity and the ability of the battery to accept the charge current in the charging environment. The ICS1708 can be
set for three (3) user-selectable fast charge rates: 15 minutes (4C), 60 minutes (1C), or 150 minutes (C/2.5). The CMN indicator is a
continuous active low during this stage. The charge rate is determined by the voltage level on the CMN indicator when the ICS1708 is first
powered-up.
A voltage acquisition window immediately follows a brief rest time after the charge pulse. No charge is applied during the rest time or
during the acquisition window to allow the battery chemistry to settle. Since no current is flowing, the measured cell voltage is not obscured
by any internal or external IR drops or noise. The ICS1708 takes samples of battery voltage during the acquisition window. The voltage
samples are averaged for comparisons to previous and subsequent averages. This method provides a most 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 equalize cells in a
multiple cell packs. The topping stage is not required before putting the battery into immediate service after fast charge completes.
The topping charge is applied for a minimum of two (2) hours. The current consists of the same pulse technique used during the fast charge
stage; however, the delay time is extended as shown in Figure 5. Extending the delay time between charge pulses allows the same charging
current used as 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 1C (1 hour) fast charge rate will occur every eleven (11) seconds for a topping charge rate of C/11. The MMN
indicator is a continuous active low during the topping and maintenance charge stages.
cycle
t im e
de la y tim e
cycle
tim e
Figure 5: Representative timing diagram for topping and maintenance charge
Maintenance Charge
The maintenance charge is intended to offset the natural self-discharge of NiCd or NiMH batteries by keeping their cells primed at peak
charge. After the topping charge ends, the ICS1708 begins this charge stage by once again extending the delay time between charge pulses.
The maintenance charge will last for as long as the divided down battery voltage is greater than 0.5V at VIN pin 7. The MMN indicator is a
continuous active low during this stage.
4
ICS1708
Charge Termination Methods
Charge termination methods include voltage slope and fast charge time out.
Voltage Slope Termination
The most distinctive point on the voltage curve of a battery in response to charging by a constant amplitude current is the voltage peak that
occurs as the battery approaches full charge. By mathematically calculating the first derivative of the voltage, a second curve can be
generated showing the change in voltage with respect to time as shown in Figure 6. The slope will reach a maximum just before peak
voltage. Using milestone voltage slope data as charging progresses, the ICS1708 determines when the point of full charge will occur and
accurately terminates the applied current when the battery reaches that point. The actual termination point is based on the actual charging
characteristics of the particular battery. Typically, fast charge ends around peak voltage.
Figure 6: Voltage and slope curves showing inflection and zero slope points
New, over-discharged, old, and already full batteries often produce a voltage profile that varies from that shown in Figure 6. The ICS1708
fast charge termination in these cases is based on a slight decrease in the voltage. Some new batteries may need several charge/use cycles
before their response fully stabilizes to that shown in Figure 6.
Charge Timer Termination
The controller uses a timer to limit fast charge duration. These times are internally set according to the charge rate selected and can be
adjusted slightly by changing the clock frequency. Fast charge timer termination is a safety backup feature to limit the duration of the fast
charge stage. The fast charge timer is always active and cannot be disabled. See Table 3 Charge Rate List.
5
ICS1708
Battery Detection
If upon initial power-up, voltage at VIN pin 7 is less than 0.5V, the ICS1708 assumes no battery is present, and the polling detect mode is
initiated.
The ICS1708 enters the polling detect mode using CHG pin 1 and applies a 100ms charge pulse. During the first 4ms pulse, the ICS1708
monitors the VIN pin 7 to determine if voltage is above the voltage set on OPREF pin 6. If the battery is present, the voltage at VIN pin 7
will be held below the voltage set on OPREF pin 6 while the current pulse is applied. If a battery is not present, the voltage at VIN pin 7 will
rise above the voltage set on OPREF pin 6.
If the voltage at VIN pin 7 exceeds the voltage set on OPREF pin 6, the ICS1708 will wait for about one-half second after the 100ms charge
pulse ends before producing another 100ms charge pulse. The process repeats until the battery connects. When the battery connects, the
100ms polling pulse is extended for another 100ms and the pulse becomes the first SoftStart conditioning pulse of 200ms. An overdischarged or low voltage battery does not interfere with a prompt start of SoftStart. The ICS1708 will automatically re-enter the polling
detect mode if the battery is removed.
Battery Removal
During the first 4ms of the application of a charge pulse, the voltage at the VIN pin 7 is compared to the voltage set at the OPREF pin 6. If
the voltage at VIN pin 7 is greater than the voltage set at OPREF pin 6 during the application of the current pulse, then the battery is
assumed to have been removed and the ICS1708 enters the polling detect mode. If the voltage at VIN pin 7 is held below the voltage set at
OPREF pin 6, charging continues.
When in the topping charge or maintenance charge stages, a charge pulse may not occur for several seconds or longer. So, during the period
between charge pulses, the voltage at VIN pin 7 is compared to the internal 0.5V reference. If the voltage at VIN pin 7 is less than 0.5V, the
ICS1708 assumes the battery has been removed, and the polling detect mode is initiated.
Pin Descriptions
In addition to a regulated +5V supply, the ICS1708 requires a few other external components to control the clock rate and provide an
indicator display. The ICS1708 is interfaced to turn on and off an external current source
Output Logic Signals: CHG pin1
The CHG pin 1 is active high/low, TTL compatible output. In addition to being TTL compatible, the CMOS output is capable of sourcing
and sinking up to 25mA which adds flexibility when interfacing to other circuitry. A logic high on CHG pin 1 indicates that the constant
current source is on. A logic low turns off the constant current source. Normal care must be taken to control wiring resistance and
inductance.
Charge Status Indicators: CMN pin 3, MMN pin 2
The controller has to two outputs for driving external indicators. These pins are active low. These two indicator outputs are open drains
when off. They can sink up to 40mA which allows for sinking LED current with use of external current limiting resistors. These two
indicator outputs denote charge status: fast charge or topping/maintenance charging as shown in Table 1.
Table 1: Indicator Description List
MMN
On
CMN
On
Flash
On
Description
Charge complete (battery ready to use) as maintenance or topping charge is applied
Fast charge (including SoftStart conditioning)
See applications information
At power-up or with battery insertion
The charge mode (CMN) indicator is low continuously during the SoftStart and fast charge stages. When the controller enters the topping
charge stage, the output turns off and the indicator turns off. When the maintenance mode (MMN) indicator is on and as the battery is ready
to use, the ICS1708 applies the topping and maintenance charge.
The ICS1708 does not control the current flowing into the battery in any way other than turning it on and off. The required current for the
selected charge rate is provided by the system's input power source. The external charging circuitry provides current at the selected charge
rate. For example, to charge a 1.2 ampere hour battery in 60 minutes (1C), 1.2 amperes is required.
6
ICS1708
Clock Input: RC Pin
The RC pin is used to set the frequency of the internal clock. Alternatively, an external 1 MHz clock may be used. Normally an external
resistor is connected between this pin and VDD. An external capacitor is connected between this pin and ground (VSS). The frequency of
the internal clock is typically 1 MHz with a 15kΩ resistor and a 100pF capacitor. All time durations noted in this document are based on a 1
MHz clock. Operating the clock at a lower frequency will proportionally change all time durations. Operating the clock at a frequency
significantly lower than 1 MHz, without adjusting the charge current accordingly, will lessen the effectiveness of the fast charge timer and
lower the accuracy of the controller. Operating the clock at a frequency greater than 1 MHz will also change all time durations and, without
adjusting the charge current accordingly, may cause termination to occur due to the fast charge timer expiring rather than by the battery
reaching full charge.
The clock may be driven by a 1 MHz external 0 to 5V pulse provided the duty cycle is between 10% and 60%. The clock input impedance is
typically 1kΩ.
Voltage Input: VIN Pin
The battery voltage is normalized by an external resistor divider network to one cell. The electrochemical potential of one cell is about 1.2V.
For example, if the battery consists of six cells in series, the voltage at the VIN pin should be set to equal to the total battery voltage divided
by six. This is accomplished with two resistors, as shown in Figure 7.
VIN pin
R1
R2
# of cells
Figure 7: Resistor divider network at the VIN pin
To determine resistor values, count the number of cells to be charged in series. Then choose either R1 or R2 and solve for the other resistor
using:
R1 = R2 * (# of cells -1) or R2 =
R1
___
(# of cells -1)
R2 value should be kept below 27K so that if a 0.047µF capacitor is used in parallel with it, more than five RC time constants
occur before data acquisition. Consult the factory for applications that require use of higher resistance voltage dividers.
Circuit Voltage Reference: OPREF pin 6
The OPREF pin has an internal 85kΩ pull-up resistor to VDD. OPREF requires an external pull-down resistor to establish the open circuit
(no battery) voltage reference. The purpose of this voltage reference is to detect the removal of the battery from the charging system. The
voltage at this pin is compared to the voltage at the VIN pin for the first 4mssec after the current source is turned on by CHG pin 1. If the
voltage at VIN is greater than the voltage set on OPREF, the ICS1708 assumes the battery has been removed and the ICS1708 enters the
polling detect mode.
For proper operation, the voltage on OPREF pin 6 is set below the (divided down) no battery voltage at VIN pin 7 produced by the current
source (when on) and above the maximum normalized voltage at VIN pin 7 with a battery present. The OPREF pin voltage must not exceed
2.3V or it will prevent the start of fast charge. If the voltage on OPREF exceeds 4V, the controller will shutdown and power to the ICS1708
must be removed and restored to restart the ICS1708.
7
ICS1708
As an example, suppose that a current source has an open circuit voltage of 12V as shown in Figure 8.
current source on (no battery)
(open circuit voltage = 12V)
+5V
+
R1 = 100k
R3 = 2.21k, 1%
OPREF = 1.89V
1.60V (battery present)
VIN = {
2.00V (no battery)
6 cells
(9.6 V)
R4 = 1.3k, 1%
-
Alternate resistor divider at the OPREF
pin for tight tolerance applications
R2 = 20k
Resistor divider at the VIN
pin
Figure 8: Open Circuit Reference Example
The maximum battery voltage of a nearly full six-cell pack with current applied is determined to be 9.6V. The voltage at OPREF should
then be set at a point between 1.6V (9.6V/6 cells=1.6V) and 2V (12V/6=2V). This can be accomplished with a pull-down resistor. Refer to
the VIN and OPREF resistor tables in the Applications Information section. From the VIN table, the divider resistors are 100kΩ and
20kΩ for R1 and R2. From the OPREF table, the pull-down resistor is 47KΩ for R3. If R3 is 47KΩ, the voltage at OPREF is typically
1.78V since the internal pull-up at the OPREF pin is 85kΩ. Figure 8 show an alternate approach for setting the voltage on OPREF for tight
tolerance applications.
Power: VDD pin 8
The power supply for the device must be connected to the VDD pin. The voltage is +5 VDC nominal, series regulated for proper noise
rejection. A 100mA or higher current rating supplies the controllers maximum of 11mA average demand that includes brief 50mA peaks.
Peripheral circuits current requirements are added to these requirements. See Pin Descriptions for additional information.
Grounding: VSS pin 6
This pin is connected directly to a solid (low impedance) ground that connects at or close to battery minus. See the section Pin Descriptions
and Applications Information (PC Board Design Considerations) for additional information.
Charge Rate Selection
The voltage set on CMN pin 3 prior to the start of fast charge sets one of three fast charge rates shown in Table 2.
Table 2: Charge Rate List
Selected Charge Rate
Topping Charge Pulse
Rate
Maintenance Charge
Pulse Rate
4C (15 min)
1C (60 min)
C/2.5 (150 min)
one every 41 sec
one every 11 sec
one every 5 sec
one every 161 sec
one every 41 sec
one every 17 sec
Fast Charge Timer
Duration (after powerup or battery insertion)
21 min
75 min
212 min
See the section on Controller Operation for additional information on the topping charge and maintenance charge. See the section on Charge Termination
Methods for additional information on the charge timer.
8
ICS1708
The 1C (60 minute rate) is selected by using a 10K pull-up resistor from CMN pin 3 to VDD pin 8 (+5V REG.) as shown in
Figure 9A "Charging System Diagram". The 10K pull-up resistor is required even if an LED with a current limited pull-up to
VDD pin 8 (+5V reg.) is used. The C/2.5 (150 minute) rate is selected using the 330/1.3K resistor divider with a general
purpose LED as shown in Figure 9B. Based on the LED selection, this configuration should provide the 2.5V +/- 0.5V on
CMN pin 3 prior to the start of fast charge to activate the C/2.5 (150 minute) rate as shown in Figure 9B. Setting the 4C (15
minute) rate involves setting the voltage at CMN pin 3 below 0.5V prior to the start of fast charge as shown in Figure 9C. A
10K pull-up resistor, a 2K pull-down resistor and a 1N4148 or equivalent diode is used to keep CMN below 0.5V at power up
or upon battery removal. When CMN goes low to ground of its own accord, the base of a 2N3903 or equivalent NPN
transistor is pulled low via the 1N4148 diode allowing the LED indication for fast charge.
CONSTANT
CURRENT
SOURCE
IN
OUT
ON/OFF
+5V REG.
+
DC INPUT
4.7uF
.047uF
ICS1708
*10K
1
R1
CHG
VDD 8
2 MMN
VIN 7
6
OPREF
RC 5
3 CMN
4
* SELECTS 1C
CHARGE RATE
VSS
15k
R3
R2
.047uF
100pF
FIGURE 9A: Charging System Diagram for 1C (60 minute) Charge Rate
9
PTC
or
TS
+
ICS1708
CONSTANT
CURRENT
SOURCE
DC INPUT
IN
OUT
ON/OFF
+
+5V REG.
4.7uF
PTC
or
TS
.047uF
ICS1708
330
1
GENERAL
PURPOSE
LED
CMN OFF=2.5V+/-.5V
FOR C/2.5 RATE
R1
CHG
VDD 8
2 MMN
3
CMN
4
VSS
VIN 7
6
OPREF
RC 5
1.3K
15k
R3
+
R2
.047uF
100pF
FIGURE 9B: Charging S ystem Diagram for C/2.5 (150 Minute) Charge Rate
CONSTANT
CURRENT
SOURCE
DC INPUT
IN
OUT
ON/OFF
+
+5V REG.
4.7uF
.047uF
ICS1708
10K
1
R1
CHG
VDD 8
2 MMN
VIN 7
6
OPREF
RC 5
3 CMN
1N4148
2N3903
4
VSS
15k
R3
R2
.047uF
100pF
2K
FIGURE 9C: Charging S ystem Diagram for 4C (15 minute) Charge Rate
10
PTC
or
TS
+
ICS1708
Data Tables
Table 3: Absolute Maximum Ratings
Supply Voltage
Input/Output Levels
Ambient Operating Temperature
Storage Temperature
6.5
-0.5 to VDD + 0.5
70
-55 to 150
V
V
°C
°C
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only.
Functional operation of the device at the Absolute Maximum Ratings or other conditions not consistent with the characteristics shown in this
document is not recommended. Exposure to absolute maximum rating conditions for extended periods affects product reliability.
Table 4: DC Characteristics
Tamb=25°C.
Parameter
Supply Voltage
Supply Current
Internal pull-up
OPREF
High Level Source Current
CHG
Low Level Sink Current
CHG
Low Level Sink Current, indicator
CMN, MMN
Symbol
Conditions
VDD
IDD
IIL
MIN
4.5
TYP
5.0
7.3
75
MAX
5.5
UNITS
V
mA
kΩ
IOH
V= VDD - 0.4V
25
mA (max)
IOL
V=0.4V
25
mA (max)
IOL
V=0.4V
40
mA (max)
Analog/Digital Converter Range
Minimum Battery Threshold
0-2.2
0-2.3
0.5
0-2.3
V
V
Table 5: Timing Characteristics
R≈15kΩ, C≈100pF
PARAMETER
Clock Frequency
Charge Pulse Width in Fast Charge Stage
Rest Time
Data Acquisition Time
Cycle Time
Polling Detect Pulse Width
Polling Detect Pulse Period
SoftStart Initial Pulse Width
SoftStart Incremental Pulse Width
Rate Select Read of CMN pin 3 at power-up or
with battery removed after fast charge starts
SYMBOL
REFERENCE
tFCHG
tR
tDA
tCYCLE
see Figure A
see Figure A
see Figure A
see Figure A
11
TYP
1.0
1048
13.0
16.4
1077
100
624
200
7.0
1160
UNITS
MHz
ms
ms
ms
ms
ms
ms
ms
ms
ms
ICS1708
Timing Diagram
Figure A:
FCHG
REST
DATA
ACQUISITION
+5V
CHG
pin 1
CYCLE
Applications Information
To ensure proper operation of the ICS1708, external components must be properly selected. The external current source used must meet
several important criteria to ensure adequate performance of the charging system. The charging current source amplitude should be fairly
constant
VIN and OPREF Divider Resistors
Figure 9 shows a typical application using the ICS1708. R1 through R3 must be selected properly to ensure that battery detection and
voltage termination methods operate properly. R1 and R2 are selected to scale the battery voltage down to the voltage of one cell. The
following table shows some typical values.
Cells
R1
R2
1
20k
*
2
20k
20k*
3
39k
20k
4
62k
20k
5
82k
20k
6
100k
20k
7
120k
20k
8
150k
20k
9
160k
20k
10
180k
20k
11
200k
20k
12
220k
20k
13 & Above
R1=R2 x (# cells - 1)
* Use 5.1V Zener as required depending on input voltage
If the current source is a switch mode type, normal ripple current does not effect the ICS1708. However, the effects of line frequency ripple
may interfere with proper performance. R3, per Figure 9, can be used to set the open circuit (no battery) reference voltage on the OPREF
pin. The function of this pin is discussed in the Open Circuit Reference section.
VOPREF
R3
43k
47k
51k
56k
62k
1.68 V
1.78 V
1.88 V
1.99 V
2.11 V
See Figure 8 for an alternate resistor divider approach at the OPREF pin for tight tolerance applications.
12
ICS1708
With the battery removed, the current source must be capable of raising the voltage at the VIN pin above the voltage at the OPREF pin to
ensure proper polling. With the batteries installed, the current source overshoot characteristics when turned on and off must not cause the
voltage at the VIN pin to approach the voltage at the OPREF pin. If the voltage at OPREF exceeds the voltage at VIN when a charge pulse
is applied, the polling feature will be activated.
PC Board Design Considerations
It is very important that care be taken to minimize noise coupling and ground bounce. Careful placement of wires and connectors helps
minimize resistance and inductance.
When designing the printed circuit board, make sure ground and power traces are wide and bypass capacitors are used right at IC power and
ground pins. Use separate heavy grounds for both signal and power circuits, connecting their grounds together close to where the negative
lead of the battery connects. For power circuits, keep the physical separation between power and return (ground) to a minimum to minimize
field effects. This precaution is most applicable to the constant current source, particularly if it is a switch mode type. Keep the ICS1708
and the constant current source control circuits outside the power and return loop described above. These precautions will prevent high
fields and coupled noise from disturbing normal operation. Avoid jumping across power and return with signal lines.
Using the Voltage Slope Termination Method
In general the voltage slope termination method works best for products where the battery is fast charged with the product off, or the battery
is removed from the product for fast charge in a charger stand.
The voltage slope termination method used by the ICS1708 requires a nearly constant amplitude current flow into the battery during fast
charge. Charging the battery in products that draw a known and fairly constant current while the battery is charging should have this current
draw added to the fast charge current. Using the ICS1708 for charging the batteries in products that randomly or periodically requires
moderate current from the battery during fast charge needs evaluation. Products that randomly or periodically require high current from the
battery during fast charge may cause a voltage inflection that results in termination before full charge. A voltage inflection can occur due to
the charge current decreasing or fluctuating as the load changes rather than by the battery reaching full charge. The voltage slope method
will terminate charge based on voltage inflections that are characteristic of a fully charged battery. The ICS1702 and ICS1712 charge
controllers have temperature termination methods for products that randomly or periodically draw significant current from the battery during
fast charge.
Charging sources that produce decreasing current as fast charge progresses may also cause a voltage inflection that may result in termination
before full charge. For example, if the charge current is supplied through a resistor or if the charging source is a constant current type that
has insufficient input voltage, the current will decrease and may cause a termination before full charge. Other current source abnormalities
that may cause a voltage inflection that is characteristic of a fully charged battery are inadequate line frequency ripple attenuation capability
or charge current decreasing due to thermal drift or thermal limiting. Charging sources that have any of the above characteristics need
evaluation to access their suitability for the application if the use of voltage slope termination is desired.
The controller SoftStart stage, built-in noise filtering, and fast charge timer operate optimally when the constant amplitude current source
charges the battery at the rate selected. If the actual charge current is significantly less than the rate selected, the conditioning effect of the
SoftStart stage and the controller noise immunity are lessened. Also, the fast charge timer may cause termination based on time duration
rather than by the battery reaching full charge due to inadequate charge current.
Charging System Status by Indicator
The Indicator Description List in Table 2 contains some displays that are caused by charging system abnormalities. When the CMN
indicator flashes, there may be voltage present at the charger terminals with the current source off with no battery connected. Check the
current source and ensure that it produces no more than 350mV at VIN pin 7 when the current source is turned off with no battery connected.
If VIN pin 7 divider resistors are not properly selected, an open circuit voltage that should produce less than 350mV with the charger off
and no battery will not divide down the open circuit voltage properly and produce the CMN flash indication. Check the VIN divider and
ensure that it properly scales the battery voltage to the 1 cell level at VIN pin 7. If the CMN flash indication occurs with the battery
installed, there may be an open connection in the charger or the battery. Check wires, connections, battery terminals, and the battery itself
for an open circuit condition.
If the MMN indicator is active at the initiation of fast charge, check the external pull-down resistor or alternate divider off 5V that sets the
voltage on OPREF pin 6. If the voltage set on OPREF is greater than 2.3V but less than 4V, the start of fast charge will be inhibited until the
voltage on OPREF is lowered.
13
ICS1708
Package Information
0.060
0.018
0.035
0.016
QuickSaver
0.250
GPI
ICS1708N
ICS1708S
YRWK
0.155
0.310
0.375
0.250
0.236
0.193
0.130
0.058
0.010
0.130
0.015
0.154
0.008
0.006
0.016
0.050
0.008
0.350
0.025
0.018
0.100
0.060
All package dimensions are in inches.
All package dimensions are in inches.
8-Pin SOIC Package (150 mil)
8-Pin DIP package (300 mil)
Ordering Information
ICS1708S, ICS1708ST, ICS1708N
Example:
ICS 1708 ST
Package type:
N=
S=
ST=
DIP 300 mil (Plastic)
SOIC 150 mil
SOIC 150 mil Tape and Reel
Device type:
Consists of 3 to 5 digits or numbers
Prefix:
ICS = Intelligent Charging Solution standard device
14
ICS1708
IMPORTANT NOTICE
Galaxy Power Incorporated makes no claim about the capability of any particular battery (NiCd or NiMH) to accept a fast charge. GPI
strongly recommends that the battery manufacturer be consulted before fast charging. GPI shall be held harmless for any misapplication of
this device such as: exceeding the rated specifications of the battery manufacturer; charging batteries other than nickel-cadmium or nickelmetal hydride type; personal or product damage caused by the charging device, circuit, or system itself; unsafe use, application, and/or
manufacture of a charging system using this device.
GPI reserves the right to make changes in the device data identified in this publication without further notice. GPI advises its customers to
obtain the latest version of all device data to verify that any information being relied upon by the customer is current and accurate.
GPI does not assume any liability arising out of or associated with the application or use of any product or integrated circuit or component
described herein. GPI does not convey any license under its patent rights or the patent rights of others described herein. In the absence of a
written or prior stated agreement to the contrary, the terms and conditions stated on the back of the GPI order acknowledgment obtain.
GPI makes no warranty of any kind with regard to this material, including, but not limited to, the implied warranties of merchantability and
fitness for a particular purpose.
GPI products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other
applications intended to support or sustain life, or for any nuclear facility application, or for any other application in which the failure of the
GPI product(s) could create a situation where personal injury or death may occur. GPI will not knowingly sell its products for use in such
applications, and the buyer shall indemnify and hold harmless GPI and its officers, employees, subsidiaries, affiliates, representatives and
distributors against all claims, costs, damages, expenses, tort and attorney fees arising out of directly or indirectly, any claim of personal
injury or death associated with such unintended or unauthorized use, even if such claim alleges that GPI was negligent regarding the design
or manufacture of the part.
COPYRIGHT © 2000 Galaxy Power Incorporated
15
ICS1708
Galaxy Power, Inc.
PO Box 890
2500 Eisenhower Avenue
Valley Forge, PA 19482-0890
Phone: 610-676-0188
FAX: 610-676-0189
WWW: www.galaxypower.com
E-mail: [email protected]
16