L4947 STMicroelectronics, L4947 Datasheet - Page 4

• Manufacturer Part Number: L4947
• Description: IC REG LDO 5V 0.5A PENTAWATT
• Manufacturer: STMicroelectronics

Specifications of L4947

• Regulator Topology: Positive Fixed
• Voltage - Output: 5V
• Voltage - Input: 6 ~ 26 V
• Voltage - Dropout (typical): 0.4V @ 500mA
• Number Of Regulators: 1
• Current - Output: 500mA
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Through Hole
• Package / Case: Pentawatt-5 (Vertical, Bent and Staggered Leads)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Current - Limit (min): -
• Other names: 497-3918-5

L4947 - L4947R
The current consumption of the device (quiescent
current) is maximum 13mA - over full T - when no
load current is required.
The internal antisaturation circuit allows a drastic
reduction in the current peak which takes place
during the start up.
The reset function supervises the regulator output
voltage inhibiting the microprocessor when the
device is out of regulation and resetting it at the
power-on after a settable delay. The reset is LOW
when the output voltage value is lower than the
reset threshold voltage. At the power-on phase
the output voltage increases (see Fig. 2) and -
when it reaches the power-on V
(On) - the reset output becomes HIGH after a de-
lay time set by the external capacitor C
power-off the output voltage decreases : at the
V
and V
Figure 1: Typical Dropout Voltage vs. T
Figure 2: Reset Waveforms:
4/6
RT(Off)
O
-0.3V typ. for L4947R value) the reset out-
threshold value (V
(I
(1) Without External Capacitor C
(2) With External Capacitor C
o
= 500mA).
O
-0.15V typ. for L4947
O
threshold V
j
d
.
d
. At the
d
.
RT
put instantaneously goes down (LOW status) in-
hibiting the microprocessor. The typical power on-
off hysteresis is 50mV.
The three gain stages (operational amplifier,
driver and power PNP) require the external ca-
pacitor (C
stability of the system.
Load dump and field decay protections ( 80V),
reverse voltage (– 18V) and short circuit protec-
tion, thermal shutdown are the main features that
make the L4947/L4947R specially suitable for ap-
plications in the automotive enviroment.
EXTERNAL COMPENSATION
Since the purpose of a voltage regulator is to sup-
ply and load variations, the open loop gain of the
regulator must be very high at low frequencies.
This may cause instability as a result of the vari-
ous poles present in the loop. To avoid this insta-
bility dominant pole compensation is used to re-
duce phase shift due to other poles at the unity
gain frequency. The lower the frequency of these
others poles at the unity gain frequency. The
lower the frequency of these other poles, the
greater must be capacitor esed to create the
dominant pole for the same DC gain.
Where the output transistor is a lateral PNP type
there is a pole in the regulation loop at a fre-
quencybtoo low to be compensated by a capaci-
tor which can be integrated. An external compen-
sation is therefore necessary so a very high value
capacitor must be connected from the output to
ground.
The paeassitic equivalent series resistance of the
capacitor used adds a zero to the regulation loop.
This zero may compromise the stability of the
system since its effect tends to cancel the effect
of the pole added. In regulators this ESR must be
less than 3
47 F.
omin
and the minimum capacitor value is
= 20 F) to guarantee the global