Datasheet SM6780AS Datasheet (NPC)

−∆

SM6780AS

NIPPON PRECISION CIRCUITS INC.

Ni-Cd/Ni-MH Battery Charger IC

OVERVIEW

The SM6780AS is a quick charge control IC for Nickel-Cadmium (Ni-Cd) and Nickel Metal Hydride (Ni-MH)
rechargeable batteries. It supports quick charge, supplemental and pulse trickle charging modes. The charging
mode is selected automatically in response to the battery voltage, temperature and charging time.

The quick charge uses either negative delta voltage detection ( −∆ V), temperature detection ( ∆ T/ ∆ t), or charg­ing time cutoff to control the charging process. In addition, the quick charge mode can be placed on hold, if the
battery voltage or battery temperature are abnormal, until normal conditions are restored.

The SM6780AS requires few external components to realize a high-stability quick charge battery charger.

FEATURES

■

Ni-Cd/Ni-MH battery quick charge control

■

V, ∆ T/ ∆ t, and maximum charge time cutoffs

■

3 charge modes (quick charge, supplemental,
pulse trickle charge)

■

3 selectable charge times (80, 120, and 240 min­utes)

■

Charge condition LED indicator output (on,
pulsed, off)

■

Low power dissipation mode

■

4.0 to 5.5V operating supply voltage

■

300sec (typ) −∆ V detection invalid time

■

8mV (typ) −∆ V detection accuracy

■

25mV/min (typ) ∆ T/ ∆ t detection accuracy

■

8-pin SOP package

PINOUT

(Top view)

TIME CHGN

LEDN

BATT

VSS

6780AS

INH
VDD
TEMP

ORDERING INFORMATION

Device Package

SM6780AS 8-pin SOP

PACKAGE DIMENSIONS

(Unit: mm)

4.4 0.2

6.2 0.3

0.695typ

1.5 0.1

1.27

5.2 0.3

0.05 0.05

0.10

0.4 0.1

M

0.12

NIPPON PRECISION CIRCUITS—1

0.15

− 0.05

0.4 0.2

+

0.1

0 to 10

BLOCK DIAGRAM

DC

Input

SM6780AS

VDD

TIMEVDD

Current

Source

Battery

Pack

NTC

BATT

TEMP

Reference

Regulators

Maximum

Cell-voltage Check

Input Select

Temp Check

A/D

OSC

−∆V

Function

Block

∆V/∆t

Function

Block

VSS

PIN DESCRIPTION

Number Name Description

1 TIME

2 LEDN

3BATT

4 VSS Ground
5 TEMP Battery temperature thermistor sensor voltage input
6 VDD Supply

7 INH

8 CHGN

Charge time select 3-level input.
HIGH: 240 minutes, MID (V

/2): 120 minutes, LOW: 80 minutes

DD

Charge indicator LED driver output.
Open-drain output. LOW-level output in quick charge mode. 1Hz pulse output when abnormal battery voltage or
temperature is detected during quick charge mode. High impedance output in supplemental and trickle charge
modes.

Battery voltage detector input.
Connect a high-impedance resistor voltage divider between the poles of the battery for v oltage detection.

Charge inhibit input.
Charging is stopped when HIGH. Charging resumes with the same charge parameters in force prior to the stop
when INH goes LOW again.

Charger control output.
Open-drain output. Battery charging current flows when CHGN is high impedance. Charge current stops when
LOW. High-impedance output in quick charge mode, and pulse output in supplemental and trickle charge
modes.

Timer Mode

Selector

Timing Control

Logic

Charge Control

Logic

CHGN

CHG Driver

VDD

LEDN

LED Driver

VDD

INH

NIPPON PRECISION CIRCUITS—2

≤

≤

≤

−

−

SPECIFICATIONS

Absolute Maximum Ratings

V

= 0V

SS

Parameter Symbol Condition Rating Unit

Supply voltage range V
Input voltage range V
Storage temperature range T
Operating temperature range T
Power dissipation P

DC Characteristics 1

DD

IN

stg

opr

D

−

−

−

−

SM6780AS

0.3 to 7.0 V

0.3 to 7.0 V
55 to 125

0 to 85

150 mW

° C
° C

V

= 4.0 to 5.5V, V

DD

= 0V, Ta = 25 ° C

SS

Parameter Symbol Condition Rating Variation Unit

Maximum temperature voltage V
High-temperature sense

voltage
Low-temperature sense voltage V

Maximum battery voltage V

V

MXT

HTS

LTS

MXV

DC Characteristics 2

V

= 4.0 to 5.5V, V

DD

Parameter Symbol Condition

VDD supply voltage V
BATT input voltage V
TEMP input voltage V
INH HIGH-level input voltage V
INH LOW-level input voltage V
TIME HIGH-level input voltage V
TIME MID-level input voltage V
TIME LOW-level input voltage V

V detection voltage range V

BATT −∆
LEDN output pulse frequency f
BATT standby voltage V
VDD current consumption I
VDD standby current I
LEDN, CHGN sink current I
INH, TIME input leakage current I
LEDN, CHGN output leakage

current

= 0V, Ta = 0 to 85 ° C unless otherwise noted

SS

DD

BATT

TEMP

IH1

IL1

IH2

IM

IL2

DET

LED

STB

DD

STB

OL

L

I

OZ

V

V

TEMP

V

V

HTS

V

> V

TEMP

V

> V

BATT

prohibition

charge cutoff 0.225V

MXT

V

TEMP

LTS

MXV

charge start 0.25V

LTS

charge prohibition 0.4V
charge cutoff or

DD

DD

DD

2.0 ±5% V

±5% V

±5% V

±5% V

Rating

min typ ma x

4.0 5.0 5.5 V
0–V

Disabled when V

< 0.5V 0.5 – V

TEMP

0.7 – – V
– – 0.1 V

V

− 0.5 – – V

DD

(V

/2) − 0.5 – (V

DD

– – 0.5 V
1–2V
–1–Hz

V

1.5 – V

DD

V

= 5V, no load – – 0.5 mA

DD

V
V
V

DD

OL

INH

= 5V, V

= V

= V

= V

BATT

+ 0.8V 10 – – mA

SS

TIME

, no load – – 1 µA

DD

= V

to V

SS

DD

––±1µA

5– –µA

DD

DD

/2) + 0.5 V

DD

0.5 V

DD

Unit

V
V

NIPPON PRECISION CIRCUITS—3

FUNCTIONAL DESCRIPTION

Charger Operation

SM6780AS

The SM6780AS battery charger operation starts
when the power is applied or when standby mode is
released. The charging operation is determined by
the BATT and TEMP pin states, and the timer mode
selected.

After charging starts, the battery voltage and temper­ature are monitored to check that they are within
quick charging rated ranges. If within rated range,
quick charge mode is selected. If outside rated range,
pulse trickle charge mode is selected.

Charging Rate

The charging rate is determined by the external
charger current source. If the quick charge mode
charging rate is considered as unity, then the supple­mental charging rate is 1/16, and the pulse trickle
charging rate is 1/256. The charging rate for supple-

286µs

Hi-Z

Low

4576µs

Quick charge uses either negative delta voltage
detection ( −∆ V), temperature detection ( ∆ T/ ∆ t), or
charging time cutoff to terminate the charging pro­cess. The charging mode changes to supplemental
charge mode when quick charge mode is completed.

Supplemental mode terminates when the charging
time finishes or battery is full, and the charging mode
changes to pulse trickle mode.

mental and pulse trickle modes are shown in figure 1.
The CHGN output is high impedance when the
charging current is flowing, and LOW when the cur­rent stops.

286µs

73.1ms

Quick charge

mode

Start
(power ON or battery insertion)

Supplemental

charge mode Pulse trickle mode

Figure 1. CHGN output (external charger control)

Charging Status Indicator LED Control (LEDN)

The SM6780AS LEDN output can be used to drive a
charging status indicator LED.

The LED timing when power is applied or standby
mode is released is shown in figure 2.

Hi-Z

LED OFF

Low

Approximately

1.5 s

Power ON or Standby mode cancel

LED ON

Approximately

3.5 s

In quick charge mode, the LEDN output is LOW and
the LED turns ON. If the battery temperature or bat­tery voltage exceeds the charging rated ranges, the
LEDN output pulses at a frequency of 1Hz to indi­cate battery out-of-range condition. In supplemental
and pulse trickle modes, the LEDN output is high
impedance and the LED turns OFF.

Depends on charge mode

Figure 2. LEDN output timing

NIPPON PRECISION CIRCUITS—4

SM6780AS

Battery Voltage and Temperature Detection

The battery voltage detector input is BATT. The
charger treats the input voltage as the equivalent
voltage of a single cell. For multiple cells (connected
in series), a high-resistance (> 100k Ω ) battery
divider can be used to input the voltage equivalent of
a single cell, as shown in figure 3.

Ra

BATT pin

The battery temperature detector input is TEMP. The
input voltage is provided by a negative temperature
coefficient thermistor (NTC thermistor) located in
close proximity to the battery, as shown in figure 4.
The input voltage range is 0.5V to V

DD

.

Battery

Rb

Figure 3. BATT connection example

Rc

Battery

NTC

Rd

Figure 4. TEMP connection example

Ra

= N − 1

Rb

N:Number of cells

TEMP pin

Note that the thermistor temperature characteristics
are non-linear, so a correction resistance Rc should
be used for linearity correction. The temperature rat­ing of resistances Rc and Rd should be chosen to

match the battery temperature range rating. If the
temperature detection function is not used, the
TEMP input should be fixed at a potential in the
range 0.25V

to 0.4V

DD

.

DD

NIPPON PRECISION CIRCUITS—5

Charging Modes

SM6780AS

<

The SM6780AS has 3 modes of operation: quick
charge, supplemental charge, and pulse trickle mode.

The SM6780AS uses the various detection functions
to monitor the state of the battery and select the
charging mode automatically.

Hi-Z

CHGN output Cell voltage

Low

Quick charge mode

Start

In quick charge mode, charging occurs at a rate set
by the external current source. In supplemental
charge mode, the battery is charged by current pulses
to the full stable capacity of the chemical substances
within the battery. Pulse trickle mode maintains the
level within the battery, compensating for internal
losses.

Supplemental

charge mode

Quick charge

mode end

Charge

complete

Pulse trickle

mode

Figure 5. Charging mode, battery voltage and charging current

Quick (Supplemental) Charge Conditions — Battery Check

The SM6780AS monitors the battery voltage and
battery temperature to confirm the values are within
the rated range of the battery during quick charge
and supplemental charging modes to realize a high­stability battery charger.

If the battery voltage or battery temperature charging
rating is exceeded before quick charging mode ter­minates, the charging mode is placed on hold. The

Low temperature sense

Maximum cell

Voltage

2.0V

0V

Charge

valid range

Voltage (0.4 × V

High temperature sense

Voltage (0.25 × V

Maximum temperature

Voltage (0.225 × V

DD)

Charge

valid range

DD)

DD)

internal timer continues to operate, and pulse trickle
charging occurs. The LEDN output pulses at a rate of
approximately 1Hz. If the charging rating is
exceeded during supplemental charging mode, the
mode terminates and charging switches to pulse
trickle mode.

VTEMP VBATT

Pulse trickle

Power ON

Pulse trickle

mode

Quick charge

start

Quick charge

mode

Quick charge
is suspended

High-temperature quick charge hold state: V
High-temperature quick charge hold release state: V

Figure 6. Quick (supplemental) charge ranges

Quick charge

restart

V

(0.225 × V

MXT

>

TEMP

Quick charge

mode

V

(0.25 × V

HTS

DD

)

)

DD

mode

TEMP

NIPPON PRECISION CIRCUITS—6

V Invalid Time

SM6780AS

−∆

Generally, the battery voltage becomes unstable just
after quick charging starts, so the −∆ V battery volt­age detection is disabled for 5 minutes to avoid error
in battery voltage detection. However, the ∆ T/ ∆t

−∆V Detection (BATT)

After Ni-Cd and Ni-MH batteries are fully charged
in quick charge mode, the battery voltage begins to
drop after reaching a peak value. The SM6780AS
monitors the delta voltage (−∆V) to help determine
when the battery is fully charged. When the voltage
has fallen a minimum of 8mV (typ), the battery is
fully charged and quick charge mode terminates.

Note that −∆V detection is disabled for 5 minutes
when quick charge mode is first started to avoid error
in battery voltage detection, as described in the pre­vious section.

∆T/∆t Detection (TEMP)

When Ni-Cd and Ni-MH batteries are close to full
charge in quick charge mode, the temperature of the
battery begins to greatly increase. The SM6780AS
monitors the temperature change rate (∆V/∆t) to help
determine when the battery is fully charged. When
the temperature voltage on TEMP decreases by a

temperature detection function continues to operate.
After the −∆V detection is enabled, both detection
functions operate.

8mV

Vpeak

Cell voltage

Quick charge time

− ∆V detect

Figure 7. Battery voltage change

minimum of 25mV (typ) within a 60-second interval,
the battery is considered to be fully charged and
quick charge mode terminates.

Note that the TEMP voltage decreases with increas­ing temperature due to the negative temperature
coefficient of the thermistor.

Cell voltage

Cell temperature

Voltage

Quick charge time

Figure 8. Battery temperature change

Voltage

Cell voltage

25mV

Quick charge time

Figure 9. V

NIPPON PRECISION CIRCUITS—7

TEMP

∆t

60s

∆T/∆t detect

change

∆T

V

TEMP

Maximum Charging Time (TIME)

SM6780AS

The SM6780AS supports 3 different maximum
charging time settings, in quick charge and supple­mental charge modes, which can be selected on the
3-level input TIME (HIGH, MID, LOW). HIGH
level is achieved by pull-up, LOW level by pull-

VDD = 5V, Ta = 25°C

TIME voltage level

min typ max

HIGH 192 240 288

MID 96 120 144

LOW648096

Quick charge/supplemental charge time (minutes)

Quick (Supplemental) Charge Inhibit (INH)

When INH goes HIGH, quick charge mode or sup­plemental charge mode operation stops. While INH
is HIGH, the internal timer stops and pulse trickle

Standby Mode

When the BATT input voltage is ≥ V
SM6780AS is in standby mode. In this mode, the
internal timer is reset, and the LEDN and CHGN

STB

, the

down, and MID level by a high-resistance voltage
divider arrangement to set the voltage at VDD/2. The
voltage level on TIME should only be switched in
standby mode.

charging occurs. When INH goes LOW, the charging
mode is restored to the previously active mode and
the internal timer restarts.

outputs become high impedance. Standby mode is
released when the voltage applied to BATT falls
below V

STB

.

NIPPON PRECISION CIRCUITS—8

Charging Flow Diagram

Supply applied

Standby mode released

LED ON

SM6780AS

(maximum battery voltage: VBATT ≥ 2V)

(battery temperature: 0.225VDD ≤ VTEMP ≤ 0.4VDD)

continuously battery check operation

Maximum quick charge time count start

Initial timer (5 minutes) count start

− ∆V detection

∆T/∆t detection

maximum charge time passed

Maximum supplemental charge time count start

LEDN = High impedance (OFF)

Battery check

and

OK

− ∆V detection disabled

∆T/∆t detection enabled

Quick charge mode

LEDN = LOW (ON)

CHGN = High impedance

or
or

Supplemental mode

CHGN = pulse

Not OK

Battery check OK
Maximum battery voltage:

and

battery temperature:

0.25VDD ≤ VTEMP ≤ 0.4VDD

Battery check not OK

VBATT ≥ 2V

Battery out-of-range

Pulse trickle mode charging

LEDN = pulse (flashing)

CHGN = pulse

Maximum charging time passed

Battery check not OK
or
maximum charging time passed

Charging terminates

Pulse trickle mode charging

LEDN = High impedance (OFF)

CHGN = pulse

NIPPON PRECISION CIRCUITS—9

Charging Operating Status

SM6780AS

Conditions

Charging status

INH

Battery

check OK

Charging mode CHGN output

1

LEDN output Internal timer

Quick charge LOW Yes Quick charge High impedance LOW (ON) Count
Quick charge hold LOW No Pulse trickle 13.68Hz, 3.91% duty 1Hz (pulsing) Count

Quick charge inhibit HIGH – Pulse trickle 13.68Hz, 3.91% duty

Same condition as

when INH went HIGH

Hold

Supplemental charge LOW OK Supplemental 218Hz, 6.25% duty High impedance (OFF) Count
Supplemental charge inhibit HIGH OK Pulse trickle 13.68Hz, 3.91% duty High impedance (OFF) Hold
Pulse trickle – – Pulse trickle 13.68Hz, 3.91% duty High impedance (OFF) –
Standby – – – High impedance High impedance (OFF) Reset

1. Frequency and duty are typical values.

TYPICAL APPLICATION CIRCUIT

External current source

VBB 12V

R1

5.1kΩ

Q1

2SC945

IN

78L05

VSS

OUT

5V

VBEQ2

Q2
2SD525

R2
4/5W

ICHG

I

CHG =

=

5 − V

R2

5 − 0.65

BEQ2

4

VDD 5V

SW1

1.8kΩ

R3
100kΩ

R4
100kΩ

R5

6

2

1

4

VDD

LEDN

TIME

VSS

R6

33kΩ

SM6780AS

CHGN

INH

TEMP

BATT

9

R

= N − 1

R10

N= Number of cells

R7
100kΩ

8

7

5

3

Q3
2SC945

R9

200kΩ

R10

200kΩ

SW2

R8
100kΩ

NTC
R:10kΩ
(at 25 C)
B:3435K

R11
640Ω

R12
12kΩ

R13
14kΩ

Note that the above circuit is an example circuit to demonstrate the connections for device functions. Battery
charger operation is not guaranteed.

NIPPON PRECISION CIRCUITS—10

SM6780AS

NIPPON PRECISION CIRCUITS INC. reserves the right to make changes to the products described in this data sheet in order to
improve the design or performance and to supply the best possible products. Nippon Precision Circuits Inc. assumes no responsibility for
the use of any circuits shown in this data sheet, conveys no license under any patent or other rights, and makes no claim that the circuits
are free from patent infringement. Applications for any devices shown in this data sheet are for illustration only and Nippon Precision
Circuits Inc. makes no claim or warr anty that such applications will be suitab le for the use specified without further testing or modification.
The products described in this data sheet are not intended to use for the apparatus which influence human lives due to the failure or
malfunction of the products. Customers are requested to comply with applicable laws and regulations in effect now and hereinafter,
including compliance with export controls on the distribution or dissemination of the products. Customers shall not expor t, directly or
indirectly, any products without first obtaining required licenses and approvals from appropriate government agencies.

NIPPON PRECISION CIRCUITS INC.
4-3, Fukuzumi 2-chome

Koto-ku, Tokyo 135-8430, Japan

NIPPON PRECISION CIRCUITS INC.

Telephone: [phone]
Facsimile: 03-3642-6698

NC9918AE 2000.05

NIPPON PRECISION CIRCUITS—11