INTEGRATED CIRCUITS
DATA SHEET
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
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
SAA1502ATS
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
PACKAGE
NAME
SSOP16
DESCRIPTION
plastic shrink small outline package; 16 leads; body width 5.3 mm
VERSION
SOT338-1
1998 Jan 15
2
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1998 Jan 15
ST
15
LEVEL
SHIFTER
VM
VCC
2
Vref
n.c.
1, 16
set
temperature
protection
charge
disable
4.18 V
ESD
6.8 V
3.95 V
VSS1
VSS2
14
3.6 V
5, 6
discharge
enable
charge
enable
BLOCK DIAGRAM
Philips Semiconductors
Safety IC for Li-ion
Cext
3
SAA1502ATS
reset
temperature
protection
CHARGE
PUMP
Vref
Vref
Vcp
LEVEL
SHIFTER
LOGIC
3
LF
4, 13
2.3 V
ESD
Vref
discharge
disable
SW2
7, 8,
9, 10
ESD
ESD
Vref
Vref
CURRENT
PROTECTION
Vd
SW1
11, 12
VM
Preliminary specification
SAA1502ATS
MGM307
Fig.1 Block diagram.
Philips Semiconductors
Preliminary specification
Safety IC for Li-ion
PINNING
SYMBOL
n.c.
V
CC
C
ext
LF
V
SS2
V
d
VM
V
SS1
ST
PIN
1, 16
2
3
4, 13
5, 6
7, 8, 9, 10
11, 12
14
15
DESCRIPTION
not connected
positive battery sense input
external delay capacitor
leadframe connection
control circuit
negative battery input and
power ground
drain voltage of SW1 and
SW2
negative sense input
ground for the control circuit
status output
handbook, halfpage
SAA1502ATS
n.c. 1
VCC 2
Cext 3
LF 4
VSS2 5
VSS2 6
Vd 7
Vd 8
MGM308
16 n.c.
15 ST
14 VSS1
13 LF
SAA1502ATS
12 VM
11 VM
10 Vd
9
Vd
Fig.2 Pin configuration.
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
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
CC
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
dch
> 1.5 mA) and will
immediately reactivate SW1, entering the discharge
enable state.
1998 Jan 15
4
Philips Semiconductors
Preliminary specification
Safety IC for Li-ion
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 I
ch
> 280 mA. As an additional safety
precaution also V
CC
> 4.18 V yields the same reaction,
because a small current of a charger may be undetected
with the condition of I
ch
> 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 V
VM
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).
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
CC
= 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
SAA1502ATS
is charged at a voltage below 2.3 V, an extra condition of
V
bat
> 2.3 V is included going from the discharge inhibit to
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
CC
−
V
VM
> 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
CC
and VM. In this
mode the voltage difference (see Fig.5) is:
V
CC
−
V
VM
= V
bat
−
V
R1
+ V
j(DO)
+ V
ds(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
V
CC
−
V
VM
= 3 V.
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
gs
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.
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
CC
, so that the charge FET will be active when
the V
VM
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
1998 Jan 15
5
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