ST3S01LED datasheet(4/17 Pages) STMICROELECTRONICS

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ST3S01LED

4/17

I.C. BLOCK DIAGRAM

POSSIBLE OPERATING MODES

Five different operating modes are allowed:

charge, precharge, reverse, charge+reverse and

precharge+reverse. These operating modes can

achieved

properly

selection

the

CMD-REVERSE CMD-PWM and CMD-MODE

(See POSSIBLE OPERATING MODE Table).

PRECHARGE MODE

The PRECHARGE function is composed by a

switch and a 100mA current source which fully

works for VCHARGE higher than 2.5V. When the

CMD-MODE and the CMD-PWM are not leaded

the switch is ON, being the input states held by an

internal pull down resistor. This is used when the

battery is strongly discharged. In this case VBATT

can be null (battery empty) and all the input pins

are

not

held

any

level

(because

the

micro-controller is down), except the VCHARGE pin

which is a main supply. The source of current

supplies a constant current into the battery till its

voltage level reaches the required level allowing to

start the micro-controller (typically 3V). The

current direction is from VCHARGE to VBATT.The

reverse leakage current when the swich is ON

must be null; this is obtained thanks to an internal

circuitry that switch OFF the internal P-MOS when

the VBATT is higher than VCHARGE,whatever the

status of the CMD-MODE. The precharge function

is also used to adjust the mean current. When the

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