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SAA1504T

Safety IC

Philips Electronics 

Philips Semiconductors

Safety IC

Objective specification

SAA1504T

Charge inhibit mode

When Vbat > 4.18 V, the charge inhibit mode will be

entered (see Fig.4). At this mode the battery can only be

discharged (CO = 0 and DO = 1).

The excess charge delay can be set by means of an

external capacitor. The delay is then defined as:

ted(det) = 30 × CCEXT with ted(det) in ms and CCEXT in nF.

When Vbat < 3.95 V, the safety IC will return from the

charge inhibit mode to the normal operating mode.

The charge inhibit mode will also be entered as soon as a

charge current is detected in the discharge enable mode

Discharge enable mode

When the safety IC is in the charge inhibit mode, charging

of the battery is disabled because SW1 is open. Initially

discharge of the battery will then occur via the backgate

diode of SW1. The load voltage will be approximately 0.6 V

lower and dissipation of the backgate diode of SW1 will

occur. It is preferable to close both switches at that time

without allowing charging of the battery until Vbat < 3.95 V.

If a discharge current is detected in the charge inhibit

mode, the system will activate the discharge enable mode,

closing both switches.

From the discharge enable mode the charge inhibit mode

will be entered again as soon as a charge current is

detected or Vbat > 4.18 V. The detection of a higher

voltage than 4.18 V is necessary. If the battery is charged

with a very low charge current, the safety IC will not switch

from the discharge enable mode to the charge inhibit

mode. Eventually, the safety IC will enter the charge inhibit

mode if the battery is overcharged to Vbat > 4.18 V

because of a small charge current.

When Vbat < 3.95 V the safety IC will return from the

discharge enable to the normal operating mode.

If the safety IC is in the charge inhibit mode, it will usually

go to the normal operating mode via the discharge enable

mode. But if the system is in the charge inhibit mode and

the battery pack is stored for several years, the battery

voltage can drop because of the battery discharge by the

safety IC 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 operating

mode should also be entered from the charge inhibit mode

when Vbat < 3.95 V and not only from the discharge enable

mode. In this way, charging a battery is always possible if

Vbat < 3.95 V.

handbook, full pagewidth

T > 100 °C

or

I > Imax

VVM > 480 mV

disable mode(1)

CO, DO

−185 mV < VVM < 175 mV

and

T < 60 °C

discharge enable

CO, DO

Vbat > 4.18 V

or

VVM < −10 mV

charge inhibit

CO, DO

Vbat < 3.95 V

Vbat < 3.95 V

to previous mode

normal operating

CO, DO

Vbat > 4.18 V

Vbat > 2.6 V

and

VVM < −185 mV

power down

CO, DO

from all modes

Vbat < 1.9 V

or

Vbat < 2.3 V at 5 ms

MGS973

(1) Minimum time in the disable mode is about 5 ms.

Fig.4 Flow diagram.

2000 Mar 07

6

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