FUNCTIONAL DESCRIPTION

The L4954 includes a monitoring circuit to warn

the microprocessor if a low voltage or no voltage

condition is occurring.

When the voltage on the STCAP pin drops below

7.5V (typ), the LVW output will go low. This tells

the microprocessor to stop executing code and

save vital information. The reset output will go low

250mV) or 4.75V is minimum value. The RESET

output doesn’t go above 0.4V until REG4 has

gone back above 4.75V (min).

Any spike will tell the microprocessor to start op-

erating. Once the STCAP line passes 7.5V (typ),

the LVWarn output will also return to high state.

The STCAP pin acts like a delay circuit. Due to

the large capacitor (470

µF), the STCAP pin al-

lows the battery voltage to decay slowly giving the

microprocessor time to store data.

Also, during short low voltage or negative voltage

conditions, the STCAP pin protects the 5V STBY

output from dropping below the RESET and LVW

trip points. The four outputs are expected to fol-

low the battery voltage down

to 11V for REG1,

9V for REG2, 6V for REG3 and REG4.

The L4954 has a STBY mode to keep the micro-

processor and memories alive during an ignition

off conditions. The EN1 input pin is controlled by

the microprocessor. A high on the EN1 input turns

on REG1, REG2, REG3, and HSD1. A Low on

EN1 places the part in stand-by mode with REG4

on. The High side driver outputs HSD2 and HSD3

are controlled by EN2 and EN3 respectively: a

Low on the control input turns the corresponding

high side driver off.

ELECTRICAL CHARACTERISTICS (Continued)

Symbol

Parameter

Test Condition

Min.

Typ.

Max.

Unit

LVWARN OUTPUT

LVW Threshold on STCAP

7.5

V

LVW Output Voltage

0

0.4

V

2.75

5

V

LVW Output Rise Time

µF

3.9

ms

LVW Output Fall Time

µF

12.6

µs

RESET OUTPUT

Reset Threshold on Reg 4

4.5

V

Reset Output Voltage

0

0.4

V

less than normal REG4 output

2.75

5

V

Reset Output Rise Time

µF

4.5

ms

Reset Output Fall Time

µF37

µs

STCAP

(V)

0

7.5

7.5

TIME

4.75

4.75

REG4

(V)

5

0

5

0.4

5

LVWarn

(V)

RESET

(V)

TIME

TIME

TIME

D95AU349A

TIMING DIAGRAM

L4954

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