Datasheet SC1766CS08TR, SC1766CS14TR Datasheet (Semtech Corporation)

© 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

BATTERY
CHARGE CONTROLLER

SC1766

Janaury 30, 1998

Note:
(1) Add suffix ‘TR’ for tape and reel.

FEATURES

• Reliable fast charge control of NiMH/NiCd

batteries

• Fast charge termination by:

1 Accurate -∆V detection level -0.25% with

respect to peak value

2 Peak voltage timer (0∆V)

• Adjustable fast charge safety timer

• Protection against temperature fault

• Protection against short-circuited and open

batteries

• Wide operation voltage range of 9V to 18V, no

extra regulator needed

• Large battery voltage detection range of 0.65V to

3.7V

• LED drivers to indicate charge status or fault

conditions

• Voltage reference output

• Quick and easy testing for production

• Space saving 8-pin and 14-pin SO packages

DESCRIPTION

The SC1766 fast charge controller IC is designed for
intelligent charging of NiMH or NiCd batteries without
overcharging. It detects a voltage drop (-∆V) occurring
in the final stage of a fast charging cycle and
correspondingly controls the charging current. Fast
charge can also be cut off by a peak voltage timer
(0∆V).

The detection of -∆V is a very reliable method to
terminate fast charging for NiMH and NiCd batteries.
The SC1766 uses -∆V detection as one of the primary
decisions for fast charge cut-off. The -∆V value of the
SC1766 is as small as 4mV per cell, particularly
suitable for NiMH as well as NiCd batteries. The peak
voltage timer is particularly useful when the voltage
drop at the end of charge for some batteries, e.g.
NiMH cells, is not pronounced enough for reliable
detection. An adjustable safety timer (3 settings) is
used as a backup termination method. Provisions are
made with the SC1766 to prevent fast charge under
temperature fault conditions. Two LED outputs are
used to indicate the charging status. Another flash LED
output can be used alone to indicate charge status.

AC mode allows the battery to drive its loads while
being charged. Test mode is provided to dramatically
reduce production test time.

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APPLICATIONS

Battery chargers for:

• Mobile phones

• Notebook and laptop personal computers

• Portable power tools and toys

• Portable communications equipment

• Portable video and stereo equipment

ORDERING INFORMATION

DEVICE

(1)

PACKAGE

SC1766CS08 SO-8
SC1766CS14 SO-14

ABSOLUTE MAXIMUM RATINGS

Parameter Symbol Maximum Units

Supply Voltage V

CC

18 V

DC Voltage Applied
to any Pin

18 V

Sink Current of V

OUT

pin, LED pin, and
FLASH pin

20 mA

Operating
Temperature Range

T

A

0 to 70 °C

Storage
Temperature Range

T

STG

-65 to 150 °C

© 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

BATTERY
CHARGE CONTROLLER

SC1766

Janaury 30, 1998

PIN CONFIGURATIONS

ELECTRICAL CHARACTERISTICS

Unless otherwise specified, TA = 25ºC, VIN = 12.5V

PIN DESCRIPTIONS

V

DD

Supply voltage input.
GND Ground.
V

BT

Input, to sense battery voltage.
MODE Input, to set IC operation mode.
TIMER Input, for safety timer control.

V

REF

Voltage reference output.
LED Output, for LED indicator.
V

OUT

Output, for LED indicator.
FLASH Output, for LED indicator (14-pin only.)
VNTC Input, for temperature protection (14 pin only).

Parameter Symbol Min Typ Max Units

Supply Voltage V

DD

918V

Supply Current I

DD

1.5 mA

-∆V detection level w.r.t. peak value

-0.25 %

Voltage protection limits
battery low
battery high

V

BT

0.50

3.30

0.65

3.70

0.80

3.90

V

Input impedance of TIMER pin Z

TIMER

100

kΩ

Input impedance of MODE pin Z

MODE

100

kΩ

Output resistance of LED pin
fast charge
trickle charge

R

LED

1

25

MΩ

Ω

Output resistance of V

OUT

pin
fast charge
trickle charge

R

VOUT

1

25

Ω

MΩ

FLASH pin output
resistance at fast charge
frequency
duty cycle

R

FLASH

25

1

50

Ω

Hz

%

Reference voltage
source current

V

REF

1.5

5.85 V
mA

Temperature fault voltage limits as
fraction of V

REF

under-temperature
over-temperature

αNTCL

0.60

0.15

0.70

0.20

0.80

0.25

V

REF

© 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

BATTERY
CHARGE CONTROLLER

SC1766

Janaury 30, 1998

TYPICAL APPLICATIONS

Step-Down High-Side Current Sense Battery Charger

NOTE: RSENSE = 0.1 ohm, CHARGE CURRENT = 0.5A ±10%, VIN > V

BAT

+3.5V

RSENSE = 0.05 ohm, CHARGE CURRENT = 1.0A ±10%, V

IN

> V

BAT

+4.0V

RSENSE = 0.033 ohm, CHARGE CURRENT = 1.5A ±10%, V

IN

> V

BAT

+4.5V

EFFICIENCY > 90%, MEASURED AT CS- NODE

NOTE: +VIN should be higher than 10V. Z1 is required when +VIN exceeds 18V. Fast charge current is ap­proximately 1A, adjustable t hrough R7. Tri ckle charge current is adjust able through R12.

Step-Down Rechargeable Battery Charger

© 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

BATTERY
CHARGE CONTROLLER

SC1766

Janaury 30, 1998

TYPICAL APPLICATIONS (cont.)

Step-Up Rechargeable Battery Charger

** CHARGING CURRENT = 0.8A, AUTO CUT-OFF AT 0.25% - DELTA-V POINT AND FAULT CONDITIONS (RIF SETS THE CHARGING CURRENT).
** V

IN

MUST BE LOWER THAN VBAT.

** SHORT CIRCUIT CONDITION IS PROTECTED WITH A 2A FUSE.

Step-Up/Down Rechargeable Battery Charger

** FAST CHARGE CURRENT =0.8A @VIN < VBAT, = (VIN - VBAT - 0.5)/0.82 @ VIN> VBAT.
TRICKLE CHARGE CURRENT = 30mA (RIF SETS FAST CHARGE CURRENT, RIT SETS TRICKLE CHARGE CURRENT).
** TYPICAL EFFICIENCY = 75%
** WITH SHORT CIRCUIT PROTECTION.

© 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

BATTERY
CHARGE CONTROLLER

SC1766

Janaury 30, 1998

TYPICAL APPLICATIONS (cont.)

Step Down Low-Side Current Sense Battery Charger

Test CircuitDischarge Circuit of

Rechargeable Battery

FINAL VOLTAGE

OF BATTERY

R26

6V 6.8K
5V 5.1K
4V 3.9K
3V 2.7K

Buzzer Circuit for Trickle Charge Mode

NOTE: Frequency (about 1Hz) is determ i ned by R33 and C33.
Buzzer will be activated when LED pin goes low.

NOTE: Frequency (about 1Hz) is determ i ned by R33 and C33.
LED will flash when LED pin goes low.

Flashing-LED Circuit for Trickle Mode

NOTE: The final voltage of battery i s determined by R26.
Discharge current is deci ded by R5. S1: Push to initiate di scharge.

© 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

BATTERY
CHARGE CONTROLLER

SC1766

Janaury 30, 1998

TYPICAL PERFORMANCE CHARACTERISTICS

© 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

BATTERY
CHARGE CONTROLLER

SC1766

Janaury 30, 1998

PRINCIPLES OF OPERATION

Battery Properties

The basic principle of rechargeable battery systems,
including NiMH and NiCd cells, is that the processes of
charge and discharge are reversible. The charge char­acteristics of NiMH and NiCd cells look similar in that

1) the cell voltage at the end of charge drops and 2)
the cell temperature increases rapidly near the end of
charge. The figure below shows the charge voltage
and charge temperature characteristics of NiMH and
NiCd cells. Notice that the cell voltage decline of NiMH
cells at the end of charge is less pronounced than for
NiCd cells.
Fast battery chargers are available where recharging

takes only 1 hour or less with a simple control circuit.
One main purpose of the control circuit is to terminate
the fast charge process to prevent the temperature and
internal pressure of the battery cell from building to a
damaging level which degrades or even destroys the
battery cell.

The SC1766 is a battery fast charge controller IC that
utilizes the following methods to terminate the fast
charge process for NiMH or NiCd battery cells:
1 Negative delta voltage cut-off (-∆V ),
2 Peak voltage timer cut-off (0∆V ),
3 Maximum temperature cut-off (TCO),
4 Maximum voltage cut-off (VCO),
5 Safety timer cut-off.

The principle of operation of the SC1766 is described
in the following section.

SC1766 Operation

When power is first applied to the charge system, con­sisting of rechargeable battery cells, charge current
source, the SC1766 and its associated external circuit,
all internal digital circuit blocks of the SC1766 are reset
by internal power-on-reset circuitry. The internal control

unit then checks the battery condition to prevent fast
charge from taking place under battery fault conditions,
i.e. cell voltage fault (VBT< 0.65V or VBT> 3.7V) or cell
temperature fault (αNTC > αNTCL or αNTC < αNTCH
for the 14-pin version). Temperature fault limits corre­sponding to αNTCL and αNTCH are determined by an
external thermistor divider circuit as included in the typ­ical application circuit. After the battery passes condi­tion fault checks, the V

OUT

pin goes to low to start fast
charge while the initial timer and safety timer of the
SC1766 start counting. Both the negative delta voltage
detector and the peak voltage timer, however, are dis­abled until the initial stage of a charge cycle elapses.

The SC1766 constantly monitors the voltage at the
VBT pin, which rises as battery cells are being fast­charged until the battery full condition is nearly ap­proached. The battery temperature is also constantly
sensed to guard against abnormal temperature situa­tions. The V

OUT

pin will be pulled high by an external
pull-up device and the fast charge process will be
switched to trickle charge when one of the following
situations is encountered:

• A negative delta voltage of 0.25% at the VBT pin is

detected compared to its peak value (−∆V),

• The battery voltage stays at its peak value for the

duration determined by the peak voltage timer set­ting (0∆V),

• The VBT pin voltage exceeds the “high” battery

voltage protection limit (VCO),

• The battery temperature, sensed by the thermistor

divider, exceeds the fault temperature range
(TCO),

• The selected safety timer period has finished.

TIMER PIN

The timer pin can be used as follows to select one of
the preset safety timer periods and its corresponding
periods of initial timer and peak voltage timer:

TIMER pin

Safety timer Peak V timer Initial timer
VDD 40 min. 2 min. 1.5 min.
GND 80 min. 4 min. 3 min.
Floating 160 min. 8 min. 3 min.

© 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

BATTERY
CHARGE CONTROLLER

SC1766

Janaury 30, 1998

PRINCIPLES OF OPERATION (cont.)

MODE PIN

The MODE pin determines the mode in which the IC
works:

MODE

Mode Function
Floating NORMAL normal operation
VDD TEST 1/512 safety timer
GND AC -∆V detector reset timer

stops (not reset)

The SC1766 will operate normally when the MODE
pin is left floating (a 0.1µF capacitor is recom­mended to be tied to the MODE pin if the charge cir­cuit works in a noisy environment). The SC1766 oth­erwise works in the following ways if the MODE pin
is biased either to VDD or to GND:

A) AC Mode (MODE pin biased to GND)
In the midst of normal charge operation, where the
VBT pin voltage is in the range from 0.8V to 3.5V
and the preset safety timer has not run out, the
safety timer will stop if the MODE pin is pulled down
to GND level. As long as the MODE pin remains low,
the VOUT pin stays ON and the LED pin OFF re­gardless of whether the battery pack voltage de­clines (-∆V present) or not. AC mode can be acti­vated by pulling the MODE pin to GND to avoid pre­mature battery charge cutoff due to fluctuating
charge current source. Switching the MODE pin af­ter the end of the safety timer has no effect on the
SC1766 display outputs, i.e., VOUT pin stays OFF
while LED pin stays ON.

B) TEST Mode (MODE pin biased to VDD)
A unique feature of the SC1766 is that it can be put
into a TEST mode by pulling the MODE pin to VDD,
allowing verification tests for the SC1766 charge cir­cuit to be performed in a few tens of seconds, ex­tremely valuable in the final phase of production.

When the SC1766 is in TEST mode, all the internal
timers are reduced by the following factors when
compared to normal operation:

1. Safety timer reduced by a factor of 512 times;

2. Initial timer reduced by a factor of 512 times;

3. Peak timer reduced by a factor of 64 times.
One critical requirement needs to be observed for the

OPERATION CHART OF THE SC1766

NO

NO

YES

YES

YES

NO

NO

NO

YES

POWER ON

IF

0.65V<VBT<3.7V

V

OUT

goes high for
trickle charge.
Safety timer and

-

∆

V detector reset.

IF

α

NTCL > αNTC

&

α

NTC > αNTCH

V

OUT

goes high for

trickle charge.

-

∆

V detector reset.

Safety timer stops.

V

OUT

goes low for fast
charge.
Safety timer starts
counting.

-∆V detector & peak
voltage timer start
working after initial
period ends.

-∆V detector & peak
voltage timer working.

IF

α

NTCL > αNTC

&

α

NTC > αNTCH

V

OUT

goes high for

trickle charge.

-

∆

V detector reset.

Safety timer stops.

IF

0.65<VBT<3.7V

V

OUT

goes high for
trickle charge.
Safety timer and

-

∆

V detector reset.

IF

Safety timer

period has

finished

IF

Peak voltage

timer period has

finished

IF

0.25% decline
of VBT is

detected

V

OUT

goes to high, fast charge finished, and trickle charge starts.

NO

YES

YES

YES

NO

© 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

BATTERY
CHARGE CONTROLLER

SC1766

Janaury 30, 1998

PRINCIPLES OF OPERATION (cont.)

-∆V detector of the SC1766 to work properly in test
mode, which is that the VBT voltage must be kept be­tween approximately 2.8V to 3.3V, rather than 0.8V to

3.5V in NORMAL mode.
If the TEST mode function is to be utilized in produc-

tion test, it has to be well planned and included in the
circuit design phase to make the voltages of the VBT
pin and MODE pins extremely controllable. In addition,
an externally controllable TIMER pin can further reduce
the test time required for testing the SC1766 in TEST
mode.

The figure below shows the timing diagram for exter­nally controlled VBT, TIMER and MODE pin voltages
of a recommended SC1766 charge circuit production
test scheme, utilizing the TEST mode function. Output
waveforms of the VOUT and LED pins (and FLASH pin
for 14-pin version) of a properly functioning SC1766
are also shown in the figure. In time segments 4, 8 and
10, the VOUT pin should change from ON to OFF, the
LED pin from OFF to ON, and the FLASH pin from ON
to flashing output (approximately 4 Hz). For the rest of
the time, the VOUT pin should remain ON, the LED pin

OFF, and the FLASH pin ON. The LED indicators work
as follows:

LED VOUT FLASH
PIN

PIN PIN
Fast Charge OFF ON ON
Trickle Charge ON OFF FLASH
VBT Abnormal OFF OFF OFF

The LED pin is used in conjunction with the VOUT pin
while the FLASH pin works alone.

Referring to the typical application circuit, the tempera­ture limits beyond where the fast charge is prohibited
can be set by choosing values for resistors and the
thermistor of the thermistor divider according to the fol­lowing formula:

R18 = 3.57 R

T1 RT2

/ (RT1-RT2)

R19 = 10 R

T1 RT2

/ (1.218RT1 - 11.2RT2)
RT1: Thermistor resistance at low temp. limit
RT2: Thermistor resistance at high temp. limit

Timing Diagram of the SC1766 in the Test Mode

© 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

BATTERY
CHARGE CONTROLLER

SC1766

Janaury 30, 1998

Battery Voltage Divider

To ensure proper operation of the SC1766, selection of
resistor values for the battery voltage divider must
meet the following two crucial requirements:

1. When the battery pack is disconnected from the
charge circuitry, the voltage of the VBT pin must be
higher than 4.0V or lower than 0.5V to put the SC1766
in reset status, where the VOUT and the LED pins be­come high impedance and the FLASH pin (only for
14-pin version) goes to high level.

2. When the battery pack is connected in normal oper­ation, the VBT pin voltage must remain in the range of

0.8V to 3.5V even when the battery pack voltage
reaches its peak when near full charge. Improper set­ting of the VBT pin voltage may cause the VOUT pin
voltage to fluctuate due to SC1766 internal protection
scheme.

Take charging an 8-cell battery pack as an example.
The highest pack voltage would be 16V when fully
charged if the highest voltage of a fully charged battery
cell is assumed to be 2V. Since the VBT pin voltage is
restricted to no higher than 3.5V, the battery voltage
divider ratio must be higher than 3.57 (16V/3.5V -1). In
other words, resistor R14 must be greater than 535kΩ.
When the battery pack is disconnected from the charg­ing circuitry the VBT pin voltage must be higher than

4.0V, dictating VBAT node voltage of the charging cir­cuitry to be higher than 17.8V (3.9V x 4.57). Practically,
however, the charging circuit supply voltage +VIN
should be higher than 18.5 in order to ensure proper
operation. In case the supply voltage +VIN can not
meet this requirement, the application circuit of the fol­lowing figure can be adopted to get around this prob­lem.

PRINCIPLES OF OPERATION (cont.)

Experimental Results

Experiments have been conducted to verify the
SC1766 operation with NiMH and NiCd battery cells of
various brands. Actual results shown in the figures be­low clearly indicate that the negative delta voltage de­tector and the peak voltage timer of the SC1766 have
precisely detected the tiny cell voltage drops or the cell
voltage peaks and consequently terminated the fast
charge process after batteries are fully charged. The
battery cell temperatures were all under safety levels.
Note that the fast charge for the NiMH battery in the
figure “Charge Characteristics of NiMH Battery” is ter­minated by the peak voltage timer (0∆V) while the fast
charge for the NiCd battery in the figure “Charge Char­acteristics of NiCd Battery” is terminated by the -∆V
detector.

Battery Voltage can be raised to
VIN = 0.9V when being charged.

© 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

BATTERY
CHARGE CONTROLLER

SC1766

Janaury 30, 1998

OUTLINE DRAWING SO-8

OUTLINE DRAWING SO-14

1. A stable constant charge current is crucial for reli­able precision -∆V detection by the SC1766 since fluc­tuation of the charge current can cause fluctuation of
the battery terminal voltage due to battery internal se­ries resistance, which will likely result in erroneous -∆V
detection by a properly functioning SC1766.

2. To prevent damage to the SC1766 from over­voltage, make sure that none of the SC1766 pins see
any voltage beyond the supply voltage, which needs to
be between +9V and +18V.

CHARGER CIRCUIT DESIGN TIPS

3. If the battery charge current is high, e.g. over 1.5A,
quality of circuit board layout and wiring connection
points become increasingly important in the charger
circuit reliability.

4. Since the SC1766 is a CMOS device, care must be
taken in handling to avoid possible damage from elec­trostatic discharge.