Philips SAA1504T-N1 Datasheet

DATA SH EET
Objective specification File under Integrated Circuits, IC17
2000 Mar 07
INTEGRATED CIRCUITS
SAA1504T
Safety IC
Philips Semiconductors Objective specification
Safety IC SAA1504T
FEATURES
Zero voltage start-up
Discharge and charge overcurrent protection
Automatic release of current protection at removal of
charger or load
Low current consumption in normal operating mode
Very low current consumption when battery voltage is
lower than 2.3 V
Accurate voltage detection levels
Continuous monitoring of batteryvoltage and charge or
discharge current
External power FETs are driven with an elevated supply voltage, reducing the on-resistance
Able to accommodate 20 V charge voltage
Read out of charge (disable) status
Small package (SO8)
Low external components count
Temperature protection
Charger reverse connection protection.
GENERAL DESCRIPTION
The SAA1504T is manufactured in a BCD Power Logic 70 process and is intended to be used as a protection circuit forsingle cell Li-ion batterypacks. The current and voltage ratings are especially designed for use in battery packs for portable telephones such as GSM.
The circuit continuously monitors the battery voltage, current and junction temperature and will disconnect the battery in case of an overload situation:
Overdischarge protection prevents deep discharge of the cell; deep discharge of a Li-ion cell degrades the life cycle
Overcharge protection for safety reasons
Overcurrent protection on charge or discharge current
rate
Temperature protection for preventing charge or discharge at high temperatures
Short circuit protection.
It must be stated that this is a safety IC to be integrated inside a battery pack. It is not primarily intended as an end of charge provision.
ORDERING INFORMATION
TYPE
NUMBER
PACKAGE
NAME DESCRIPTION VERSION
SAA1504T SO8 plastic small outline package; 8 leads; body width 3.9 mm SOT96-1
2000 Mar 07 3
Philips Semiconductors Objective specification
Safety IC SAA1504T
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BLOCK DIAGRAM
handbook, full pagewidth
MGS969
set disable mode
reset disable mode
LOGIC
CHARGE
PUMP
LEVEL
SHIFTER
LEVEL
SHIFTER
CURRENT
PROTECTION
K2 × V
ptat
V
ref
V
cp
V
CC
K1 × V
ptat
V
ref
185 mV
175 mV
3.95 V
4.18 V
2.3 V
ESD
ESD 6.8 V
SAA1504T
8
7
1
6
5
4
n.c.
V
CC
CEXT
V
SS
VM
ST
ESD
DO
CO
2
3
ESD
ESD
ESD
Fig.1 Block diagram.
Philips Semiconductors Objective specification
Safety IC SAA1504T
PINNING FUNCTIONAL DESCRIPTION
The basic function of the SAA1504T is to protect a single Li-ion cell against overcharge and overdischarge for reasons of life time and safety. The voltage across the cell terminals (V
bat
) is monitored continuously and compared
to an accurate internal reference voltage. The circuit diagram (see Fig.3) of a Li-ion battery pack
shows the SAA1504T and 2 power NMOS transistors which are connected in anti series. Both transistors must have their backgate connected to their source, resulting in 2 backgate diodes in anti series.
The timing diagram (see Fig.6) shows the detection levels for the various modes of operation.
Battery voltage between 2.6 and 4.18 V
The safety IC is in the normal operating mode for V
bat
= 2.6 to 4.18 V, a charge or discharge current below the current-protection level and a junction temperature below the temperature protection activation level. In this mode transistors SW1 and SW2 are driven with an elevated supply voltage (with a charge pump) which guarantees a low on-resistance in the main current path. This is important for fully utilizing the high energy density of the Li-ion battery technology.
SYMBOL PIN DESCRIPTION
V
SS
1 ground supply DO 2 output to gate of discharge power FET CO 3 output to gate of charge power FET VM 4 negative sense input ST 5 status output n.c. 6 not connected CEXT 7 connection for external delay capacitor V
CC
8 positive battery sense input
handbook, halfpage
1 2 3 4
8 7 6 5
MGS970
SAA1504T
V
CC CEXTDO n.c.
ST
VM
CO
V
SS
Fig.2 Pin configuration.
handbook, full pagewidth
MGS971
C1
0.47 µF
C2
SW2
2
ST
5
3
1
7
SW1
DO
CEXT
V
SS
CO
VM
4
8
SAA1504T
V
bat
R1
1 k
+ charger/load
charger/load
V
CC
Fig.3 Safety IC connection diagram.
Philips Semiconductors Objective specification
Safety IC SAA1504T
Battery voltage below 2.3 V
When V
bat
< 2.3 V the safety IC is in the Power-down
mode: SW2 is open to block a further discharge. The battery voltage will increase stepwise, because of the
sudden disconnection of the load. The safety IC will not re-enter the normal operating mode at this event unless the battery voltage exceeds the power-down release level of 2.6 V and a charge current is present. So when no charger is present in the Power-down mode, the safety IC stays in this mode, independent of the battery voltage.
ConnectingachargerinthePower-downmodeisdetected by a negative voltage on pin VM. Because the voltage at pin VM is defined by a charge current via the backgate diode of SW2, a charge current of a few nAs is already detected. When a charge current is detected and V
bat
> 2.6 V, the system will go from the Power-down
mode to the normal operating mode. In the Power-down mode the supply current is reduced to
150 nA (typical value) for minimizing the discharge of the battery by the safety IC. This is achieved by disabling all analog circuitry, except the circuitry for detecting the presence of a charger and for detecting V
bat
> 2.6 V. Because the charge pump is disabled and battery charging should be possible, SW1 is switched on with a reduced Vgs voltage.
Battery voltage above 4.18 V
When the battery is charged to V
bat
> 4.18 V, the safety IC will enter the charge inhibit mode: SW1 is open and charging is disabled.
Connecting a load in the charge inhibit mode is detected by the reversal of the voltage across SW1 and will immediately close SW1, so entering the discharge enable mode. A short time is needed to charge the gate of SW1. During this time the backgate diode between drain and source of SW1 conducts.
The safety IC will remain in the discharge enable mode unless:
V
bat
< 3.95 V, which results in re-entering the normal operating mode. This transition is not externally noticeable, because both switches remain closed.
A charger is connected, which will immediately open SW1. As an additional safety precaution V
bat
> 4.18 V also yields the same reaction, because otherwise a smallcurrentof a charger may be undetected, leading to overcharging the Li-ion cell.
Zero voltage start-up
The safety IC has to be able to charge the battery at 0 V. This means that when connecting a charger in case of a completely empty battery, SW1 has to be open.
In the Power-down mode output CO is connected via a diode to VCC, so that the charge transistor will be active when VVM is negative.
Maximum charge or discharge current and temperature protection
When the maximum charge or discharge current is exceeded or when the maximum temperature is detected the disable mode is activated and will open both switches. Exceeding the maximum charge or discharge current is detected by a voltage drop or rise on pin VM when both switches are closed.
A release of this mode can only be achieved by removing the load (or charger) and at a junction temperature below 60 °C. The disable mode is followed by a return to its previous mode.
Normal operating mode
In case of correct temperature, battery voltage and charge or discharge current, the system will be in the normal operating mode (see Fig.4).
Both the charge and discharge outputs will be HIGH (CO = 1 and DO = 1), so both switches are closed.
Power-down mode
When V
bat
< 2.3 V the safety IC will enter the Power-down mode(seeFig.4).Thepower-down detection level of 2.3 V hasadelay of 5 ms (typical value). The Power-down mode will also be entered without delay when V
bat
< 1.9 V.
In this mode only charging of the battery is allowed (CO = 1 and DO = 0).
The safety IC will return to the normal operating mode as soon as V
bat
> 2.6 V and a charge current is detected at
the same time.
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