l4954 STMicroelectronics, l4954 Datasheet - Page 5

• Manufacturer Part Number: l4954
• Description: Quad Multifunction Voltage Regulator For Car Radio
• Manufacturer: STMicroelectronics

ELECTRICAL CHARACTERISTICS (Continued)
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
when REG4 (5V-STBY) drops below (V
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 F), the STCAP pin al-
TIMING DIAGRAM
LVWARN OUTPUT
RESET OUTPUT
Symbol
TH
TH
V
V
t
t
t
t
LVW
rise
RES
rise
fall
fall
LVW
RES
LVW Threshold on STCAP
LVW Output Voltage
LVW Output Rise Time
LVW Output Fall Time
Reset Threshold on Reg 4
Reset Output Voltage
Reset Output Rise Time
Reset Output Fall Time
Parameter
LVWarn
STCAP
RESET
REG4
(V)
(V)
(V)
(V)
0.4
0
5
0
5
5
REG4
STCAP <7.5V; V
STCAP >7.5V V
C
C
Set V
V
Set V
less than normal REG4 output
voltage; V
C
C
IL
LVW
LVW
RESET
RESET
= ”0”
7.5
S
S
= 0.1 F
= 0.1 F
-
4.75
so that V
so that V
= 0.1 F
= 0.1 F
Test Condition
IH
4.75
= ”1”
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.
7.5
OUT5STBY
OUT5STBY
IH
IL
= ”1”
= ”0”
D95AU349A
<4.5V;
is not
TIME
TIME
TIME
TIME
Min.
2.75
2.75
0
0
Typ.
12.6
7.5
3.9
4.5
4.5
37
Max.
0.4
0.4
5
5
L4954
Unit
ms
ms
V
V
V
V
V
V
s
s
5/7