Philips saa1502bts DATASHEETS

INTEGRATED CIRCUITS

DATA SH EET

SAA1502ATS

Safety IC for Li-ion

Preliminary speciﬁcation File under Integrated Circuits, IC11

1998 Jan 15

Philips Semiconductors Preliminary speciﬁcation

Safety IC for Li-ion SAA1502ATS

FEATURES

• Integrated power switches

• Temperature protection

• Zero voltage start-up

• Discharge and charge overcurrent protection

• Automatic release of current protection at removal of

charger or load

• Extremely low current consumption when battery voltage is lower than 2.3 V

• Low current consumption in normal operation mode

• Accurate voltage detection levels

• Low resistance in current path

• Able to accommodate 17.5 V charge voltage

• Read out of charge disable status

• Small package (SSOP16)

• Low external components count

• Continuous monitoring of the battery voltage and

(dis)charge current.

GENERAL DESCRIPTION

The SAA1502ATS is manufactured in a Bipolar, CMOS and DMOS (BCD) Power Logic 70 process and is intended to be used as a protection circuit for single cell Li-ion battery packs. The current and voltage ratings are especially designed for use in battery packs for portable telephones such as GSM. The circuit monitors the battery voltage, current and 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 lifetime

• Overcharge protection for safety reasons

• Overcurrent protection on charge as well as discharge

current rate

• Temperature protection for preventing charge or discharge at high temperatures.

It must be stated that the unit is a safety unit to be integrated inside a battery pack. It is not intended as an end of charge provision.

ORDERING INFORMATION

TYPE

NUMBER

SAA1502ATS SSOP16 plastic shrink small outline package; 16 leads; body width 5.3 mm SOT338-1

NAME DESCRIPTION VERSION

PACKAGE

1998 Jan 15 2

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1998 Jan 15 3

book, full pagewidth

BLOCK DIAGRAM

Safety IC for Li-ion SAA1502ATS

Philips Semiconductors Preliminary speciﬁcation

n.c.

SS1

SS2

LEVEL

ESD

SW2

SHIFTER

ESD

ref

4.18 V

3.95 V

3.6 V

2.3 V

ref

set temperature protection

charge

disable

charge enable

discharge

enable

discharge

disable

ref

1, 16

5, 6

4, 13

7, 8, 9, 10

ESD 6.8 V

LOGIC

ext

reset temperature protection

CHARGE

PUMP

LEVEL

SHIFTER

CURRENT

PROTECTION

ref

SAA1502ATS

ref

SW1

11, 12

MGM307

Fig.1 Block diagram.

Philips Semiconductors Preliminary speciﬁcation

Safety IC for Li-ion SAA1502ATS

PINNING

SYMBOL PIN DESCRIPTION

n.c. 1, 16 not connected V

ext

LF 4, 13 leadframe connection

SS2

VM 11, 12 negative sense input V

SS1

ST 15 status output

2 positive battery sense input 3 external delay capacitor

control circuit

5, 6 negative battery input and

power ground

7, 8, 9, 10 drain voltage of SW1 and

SW2

14 ground for the control circuit

handbook, halfpage

V V

n.c.

V C

SS2 SS2

ext

V V

d d

1 2 3 4

SAA1502ATS

5 6 7 8

MGM308

n.c.

ST V

SS1

VM V

FUNCTIONAL DESCRIPTION

Figure 3 gives the connection diagram of a Li-ion battery pack. All that is contained within the solid perimeter is the safety IC SAA1502ATS. It is a Multichip Module (MCM), containing two separate but interconnected chips, one is the control IC and the other contains two vertical power NMOS transistors which are connected in anti series. Both transistors have their backgate connected to their source, resulting in two backgate diodes in anti series. The basic function of the SAA1502ATS is to protect a single Li-ion cell against overcharge and overdischarge for reasons of lifetime and safety. The voltage across the cell terminals is monitored continuously and compared to an accurate internal reference voltage. For battery voltages between 3.6 and 4.18 V and a (dis)charge current below the current protection level, the safety unit is in normal operating mode (see Fig.4). In this state both switches are driven with an elevated supply voltage (with a charge pump) which guarantees a low resistance in the main current path. This is important for fully utilizing the high energy density of Li-ion battery technology.

The discharge PowerMOS transistor SW2 is disabled to block further discharge, when the battery is discharged below 2.3 V. The battery voltage will increase stepwise, because of the sudden disconnection of the load. The unit will not re-enter the normal operation mode at this event

Fig.2 Pin configuration.

unless the battery voltage exceeds the voltage restarting level of 3.6 V.

When no charger is present in the discharge inhibit mode, the system will switch to the Power-down mode.

The current consumption of the unit (SAA1502ATS and the Li-ion cell) is then reduced to a typical value of 0.1 µA for minimizing the discharge of the battery pack.

Connecting a charger in the Power-down mode is detected by a voltage difference between V

and VM of more than

3 V. The system will then return to the discharge inhibit mode. After a short transition phase characterized by conduction of the backgate diode between the drain and source leads of SW2, the system goes to the normal operating mode and SW2 is powered again.

At zero voltage start-up, the system will start at the reset mode. A special circuit keeps the charge transistor SW1 on as much as possible.

When the battery is charged to a voltage level of 4.18 V it will enter the charge inhibit mode and the charge PowerMOS transistor SW1 is switched off, disabling charging. Connecting a load is then detected by the reversal of the voltage across SW1 (I

> 1.5 mA) and will

dch

immediately reactivate SW1, entering the discharge enable state.

1998 Jan 15 4

Philips Semiconductors Preliminary speciﬁcation

Safety IC for Li-ion SAA1502ATS

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 system will remain in the discharge enable mode unless:

• The battery voltage drops below 3.95 V, which results in re-entering normal operation. This transition is not externally noticeable, because both switches remain low ohmic.

• A charger is connected which will immediately deactivate SW1 if Ich> 280 mA. As an additional safety precaution also VCC> 4.18 V yields the same reaction, because a small current of a charger may be undetected with the condition of Ich> 280 mA, leading to overcharging the Li-ion cell.

Current protection will deactivate both switches and is detected by a voltage drop or rise of VVM when both switches are activated. A release of this state can only be achieved by removing the load (or charger).

The temperature protection overrules all other states and yields deactivation of both switches. This situation is activated at a junction temperature of 130 °C and released at a junction temperature of 60 °C. The temperature protection is followed by a return to its preceding mode.

Normal mode

In case of correct temperature, battery voltage and (dis)charge current, the system will be in the normal operation mode. Both the charge and discharge output will be active high, so both switches are conducting (SW1 = SW2 = 1).

is charged at a voltage below 2.3 V, an extra condition of V

> 2.3 V is included going from the discharge inhibit to

bat

the normal operation mode.

Power-down mode

At low battery voltage the supply current is reduced to 100 nA for minimizing the discharge of the battery by the SAA1502ATS.

At the Power-down mode all analog circuitry, except circuitry for detecting a charger present (V

− VVM> 3 V),

is disabled. The Power-down mode is entered when the system is in the discharge inhibit mode and no charger is present. The discharge inhibit mode will be entered again as soon as a charger is connected.

The detection of a charger is accomplished by detecting a voltage difference of 3 V between V

and VM. In this

mode the voltage difference (see Fig.5) is: VCC− VVM=V

− VR1+V

bat

j(DO)+Vds(CO)

≈ V

bat

+ 0.6 V.

So in the application the battery has to be charged in the Power-down mode until such a voltage that VCC− VVM=3V.

Reset mode

If the battery voltage is below 1.9 V, the system will be in the reset mode. Because in this mode the charge pump is disabled and battery charging should be possible, the charge FET is switched on with a reduced V

voltage.

As soon as the battery voltage exceeds 2.25 V the system will switch to the discharge inhibit mode and the charge pump will be activated again.

Discharge inhibit mode

If the battery drops below 2.3 V, the system will switch to the discharge inhibit mode. In this mode only charging of the battery is allowed (SW1 = 1, SW2 = 0). The system will return to the normal operation mode as soon as the battery voltage will exceed 3.6 V, or by detection of a charge current.

The overdischarge detection of 2.3 V has a delay of 40 ms typical. The voltage detection level 3.6 V has a delay of 50 ms typical. Because a charge current is necessary to increase the battery voltage, the system will normally switch to the normal operation mode at V

= 2.3 V by

detecting a charge current. But if the charge current is too small to detect, the 3.6 V detection is a backup.

To prevent an instable situation between the normal operation and the discharge inhibit mode when the battery

1998 Jan 15 5

Zero voltage start-up

The system has to be able to charge the battery at ‘0 Volt’. This means that when connecting a charger in case of a complete empty battery, the charge FET has to be active. In the reset mode the charge FET (SW1) is connected via a diode to V

, so that the charge FET will be active when

the VVM voltage is negative. The discharge inhibit mode will be entered as soon as a battery voltage exceeds

2.25 V.

Charge inhibit mode

If the battery voltage exceeds 4.18 V, the charge inhibit mode will be entered. At this mode the battery can only be discharged (SW1 = 0, SW2 = 1). The overcharge detection has a delay of 40 ms. This delay can be increased by an external capacitor. The delay time is then

Philips Semiconductors Preliminary speciﬁcation

Safety IC for Li-ion SAA1502ATS

defined as: td= 40 + (37 × C

) [ms], with C

ext

in nF.

The system will return to the normal operation mode from the charge inhibit mode when the battery voltage drops below 3.95 V.

From the discharge enable mode the charge inhibit mode will also be entered as soon as a charge current is detected.

Discharge enable mode

When the system is in the charge inhibit mode, charging of the battery is disabled because switch SW1 is turned off. Discharge of the battery will then occur via the backgate diode of SW1. So the output voltage will be approximately

0.6 V lower and also dissipation of the backgate diode of

SW1 occurs. It would be preferable to turn both switches on at that time without allowing charging of the battery until the battery voltage has dropped to 3.95 V.

If a discharge current larger than 1.5 mA is detected in the charge inhibit mode, the system will activate the discharge enable mode, activating both switches. From the discharge enable mode the charge inhibit mode will be re-entered as soon as a charge current is detected larger than 280 mA or the battery voltage exceeds 4.18 V.

The detection of a higher voltage than 4.18 V is a backup. If the battery is charged with a lower charge current than 280 mA, the system will not switch from the discharge enable mode to the charge inhibit mode. Eventually, if the battery is overcharged because of a small charge current, the battery voltage will exceed 4.18 V and the system will switch to the charge inhibit mode.

The system will return to the normal operation mode from the discharge enable mode when the battery voltage drops below 3.95 V.

If the system is in the charge inhibit mode, it will mostly go to the normal mode via the discharge enable mode. But if the system is in the charge inhibit state and the system is stored for several years, the battery voltage can drop because of the battery discharge by the SAA1502ATS and the self-discharge of the battery. So a voltage drop of the battery is possible, without detecting a discharge current. Because of this, the normal operation mode should also be entered from the charge inhibit state when the battery voltage is below 3.95 V and not only from the discharge enable mode. In this way, charging a battery is always possible if the battery voltage is below 3.95 V.

Temperature protection

Internally the system will switch between the different modes as given in the state diagram, independent of the temperature. As the junction temperature exceeds 130 °C, the output signals will be overruled and switched to zero (SW1 = SW2 = 0).

The supply current will be reduced to approximately 100 nA when the Power-down or reset mode is activated. In these modes the temperature protection is deactivated.

When the junction temperature drops below 60 °C, the output signals will not be overruled any more.

Overcurrent protection

When the (dis)charge current exceeds the specified maximum value, the current protection mode is entered.

An extra condition of SW1 = SW2 = 1 is necessary because of the next situation:

If the system is in the discharge inhibit and a charge current is detected (e.g. V

= −0.6 V) the normal

operation mode will be entered. Because of a minimum time in which the gate capacitors have to be charged, the VVM voltage will be −0.6 V for a short period, when the system is already in the normal operation mode. A V

voltage of −0.6 V could also occur when the system is charged with current exceeding the maximum charge current. To prevent that a maximum charge current is detected when coming from the discharge inhibit state, the system waits until both SW1 and SW2 are fully charged before a maximum (dis)charge current is detected.

So the voltages at SW1 and SW2 are measured to be sure that the normal operation mode is stabilized before the current protection mode can be entered.

The same applies when entering the discharge enable state from the charge inhibit state by detecting a discharge current.

The delay of the current protection as function of the (dis)charge current is given in Fig.8.

1998 Jan 15 6

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