INTEGRATED CIRCUITS
DATA SHEET
SAA1501T
Battery charge level indicator
Objective specification
File under Integrated Circuits, IC11
December 1994
Philips Semiconductors
Philips Semiconductors
Objective specification
Battery charge level indicator
FEATURES
•
High level of integration to allow assembly in intelligent
battery packs
•
Accurate charge and discharge account
•
Large dynamic range of charge and discharge currents
•
Independent settings of charge and discharge efficiency
•
2 V minimum supply voltage (2 cell operation)
•
Temperature protection of batteries during charging
•
Temperature controlled self-discharge
•
Accurate charge current regulation
•
Two charge amount display modes, LCD and LED.
GENERAL DESCRIPTION
SAA1501T
The SAA1501T is intended to be used as a battery monitor
and charge current control circuit in rechargeable battery
systems.
The SAA1501T is processed in BiCMOS technology
where the benefits of mixed bipolar and CMOS technology
is fully utilized to achieve high accuracy measurements
and digital signal processing in the same device. The
general function of the integrated circuit is a Coulomb
counter. During battery charging, the charge current and
charge time are registered in a Coulomb counter. During
discharge, the discharge current and time are recorded.
The momentary charge amount of the batteries can be
displayed either on an LCD screen or on an LED bargraph.
Using the SAA1501T, intelligent batteries or intelligent
battery powered systems can be easily designed with only
a few external components.
QUICK REFERENCE DATA
SYMBOL
V
CC
I
CC
I
CCstb
f
osc
V
i(s)
T
amb
PARAMETER
supply voltage
supply current
supply current in standby mode
fixed oscillator frequency
input sense voltage (pins 9 and 10)
operating ambient temperature
V
CC
= 3 V;
I
c
= I
d
= 60
µA
V
CC
= 3 V;
V
CSI
= V
DSI
= 0 V
C
osc
= 820 pF;
R
ref
= 51.5 kΩ
CONDITIONS
−
−
−
0
0
MIN.
2.0
TYP.
3.0
1.2
−
4.2
−
−
MAX.
4.3
1.7
100
−
UNIT
V
mA
µA
kHz
V
CC
−
1.6 V
+70
°C
ORDERING INFORMATION
PACKAGE
TYPE NUMBER
NAME
SAA1501T
SO24
DESCRIPTION
plastic small outline package; 24 leads; body width 7.5 mm
VERSION
SOT137-1
December 1994
2
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December 1994
BLOCK DIAGRAM
Philips Semiconductors
Battery charge level indicator
3
Objective specification
SAA1501T
Fig.1 Block diagram.
Philips Semiconductors
Objective specification
Battery charge level indicator
PINNING
SYMBOL
V
CC
EN
C
cy
C
CC
I
ch
R
ref
R
DCC
R
CCC
CSI
DSI
R
TEMP1
R
TEMP2
C
osc
BUZ
FULL
L100
L80
L60
L40
L20
BP
BLI
POL
GND
PIN
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
DESCRIPTION
supply voltage
enable output
duty cycle capacitor output
charge counter capacitor output
maximum average charge current
setting input
current reference resistor input
discharge current conversion resistor
input
charge current conversion resistor
input
charge sense input
discharge sense input
temperature sensing resistor 1 input
temperature sensing resistor 2 input
oscillator capacitor input
buzzer output
battery full indication output
100% segment indication output
80% segment indication output
60% segment indication output
40% segment indication output
20% segment indication output
LCD back plane drive
battery low indicator LED output
power-on LED output
power ground
SAA1501T
Fig.2 Pin configuration.
December 1994
4
Philips Semiconductors
Objective specification
Battery charge level indicator
FUNCTIONAL DESCRIPTION
The most important function of the SAA1501T is the
charge account in rechargeable battery systems. Both
NiCd and NiMH batteries in all sizes can be used. The
system can operate alone as a charge monitor with a
charge amount display function or, can operate in
conjunction with a charger. If the SAA1501T operates
together with a charger, it delivers a control signal at output
EN, for charge current regulation or for battery voltage
regulation.
Fast charging systems and charge current regulation
The SAA1501T is especially designed to be used in fast
charging systems. In fast charging systems, the charge
time is lowered by raising the charge current. Signal EN
controls the charger current. The counters register the
state of charge of the batteries and at the 80% level the
charge current is reduced via a smaller duty cycle
regulation of signal EN. The second (slow) level fully
charges the batteries which is not possible with the first
(fast) level. After the slow charge mode the counter
switches over to an even smaller duty cycle of EN and thus
enters the third (trickle) charge mode, to overcome the
self-discharge of the batteries.
Current sensing and charge account
The charge current is sensed by means of a very low
resistance (e.g. 70 mΩ) sense resistor R
sc
(see Fig.8) to
save power at high charge rates. Via the V/I charge
converter and external resistor R
CCC
(see Fig.8), the
sensed voltage is converted into a charge current I
c
(the
same is applicable for the discharge current). In the I/F
converter the charge current is converted into a frequency
for up-counting the counter. For the discharge current (I
d
)
the converted frequency is used for down-counting. The
up and down counting is registered in counters CNT1 and
CNT2, depending on the actual charge and discharge
current levels of the batteries. This is called dynamic
charge account.
Charge display
The charge amount represented by the Coulomb counter
can be displayed via an LCD screen or via an LED
bargraph. If the charge amount is reduced to 0%, the
battery low indicator (BLI) LED is turned on at the end of a
battery discharge session. A flashing BLI, in combination
with a repeating buzzer alarm, informs the user about the
low charge state. A new charge session should then be
started.
Protections
SAA1501T
In the temperature control block, the absolute temperature
is used as a protection to end the fast charge cycle. Fast
charging at high temperature is not permitted because of
degradation of the battery cells. If the batteries are
disconnected, an open-battery condition is recognized and
the SAA1501T enters the standby mode.
Mode detection
The mode detector detects whether there are any charge
or discharge currents, whether the system is powered,
whether loads are connected or whether the system is in
the standby mode. If power is connected, the power-on
LED (POL) is on. In the standby mode, the Coulomb
counter will count down in accordance with the
self-discharge speed of the batteries, which is temperature
controlled. The following subsections describe the various
blocks of the block diagram in more detail.
Supply and reference
During the period when V
CC
rises from 0 V to the internal
reset level, all counters are reset. The internal reset is
released before V
CC
reaches 1.7 V. The operating supply
voltage ranges from 2 V to the open battery level of
4.3 V (min). The characteristics are guaranteed at
V
CC
= 3 V. In order to protect the SAA1501T against high
supply voltages during open battery in a flyback converter,
a voltage clamp circuit is made active at 6.35 V (typ). The
clamping current must not exceed 80 mA. A band gap
reference block is included to generate accurate voltages
i.e. for the oscillator. Moreover, together with R
ref
, accurate
currents are generated which are used in the I/F and V/I
converters and the oscillator block. In the standby mode
only the oscillator and the digital parts are active to limit the
discharge current of the batteries to a current level of less
than 100 mA. The circuits that are needed temporarily are
switched on and off during standby (see “Timing
characteristics” t
som
).
Voltage-to-current charge and discharge
In the V/I converter, the input charge current is translated
into acceptable levels for the circuit. The conversion
formula is:
(
I
ch arg e
×
R
sc
)
I
c
=
-------------------------------------- ; where R
CCC
> R
sc
(see Fig.7)
-
R
CCC
December 1994
5
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