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SAA1504T Ver la hoja de datos (PDF) - Philips Electronics

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SAA1504T
Philips
Philips Electronics Philips
SAA1504T Datasheet PDF : 16 Pages
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Philips Semiconductors
Safety IC
Objective specification
SAA1504T
Battery voltage below 2.3 V
When Vbat < 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.
Connecting a charger in the Power-down mode is detected
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
Vbat > 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 Vbat > 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 Vbat > 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:
Vbat < 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 Vbat > 4.18 V
also yields the same reaction, because otherwise a
small current of 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 Vbat < 2.3 V the safety IC will enter the Power-down
mode (see Fig.4). The power-down detection level of 2.3 V
has a delay of 5 ms (typical value). The Power-down mode
will also be entered without delay when Vbat < 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 Vbat > 2.6 V and a charge current is detected at
the same time.
2000 Mar 07
5

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