SAA1502ATS Просмотр технического описания (PDF) - Philips Electronics

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SAA1502ATS

Safety IC for Li-ion

Philips Electronics 

Philips Semiconductors

Safety IC for Li-ion

Preliminary specification

SAA1502ATS

defined as:

td = 40 + (37 × Cext) [ms], with Cext 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. VVM = −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 VVM

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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