SI-3018LSA
LOW-VOLTAGE, HIGH-CURRENT
1.8 V LINEAR REGULATOR
APPLICATIONS INFORMATION
Thermal protection and heat sinking.
Thermal protection
circuitry turns off the device should the junction temperature rise
above 135°C. This is intended only to protect the device from
failures due to excessive junction temperatures and should not
imply that high-temperature operation is permitted. Ambient
temperature is affected by air circulation and proximity to other
heat-producing components. Normal operation is resumed when
the junction temperature is reduced. Output terminals 7 and 8
are the lead frame and substrate of the pass transistor and
provide a low thermal-resistance path for heat sinking.
In general, the maximum ambient temperature has the most
effect on determining the heat sinking that is needed to maintain
a safe normal operating junction temperature. The maximum
heat sinking thermal resistance (R
θJA
) can be calculated as
R
θJA
= (135 – T
A
) / I
O
(V
I
– 1.8)
down resistor. If this terminal is not connected (open-circuit
fault), the device output is turned off.
Overcurrent protection.
The SI-3018LSA includes an
overcurrent protection circuit, which limits the output current at
start up. It thus cannot be used with
1) a constant-current load,
2) a power supply with positive and negative to a common load
(center-tap type power supply),
3) a series power supply, or
4) a diode or resistor in series with the device ground to raise
the output voltage.
Input voltage.
Including ripple voltage and transients, the
minimum input voltage should be greater than the sum of the
output voltage and the maximum rated dropout voltage; the
maximum input voltage must be less than the absolute maximum
rated input voltage (16 V).
In most applications, the input voltage (terminal 1, V
I
) and
the supply voltage (terminal 3, V
S
) are connected together.
Output capacitor.
A 22
µF
tantalum electrolytic capacitor is
recommended between the output and ground. Very-low ESR
capacitors should not be used.
Input capacitor.
A 0.1
µF
to 10
µF
tantalum capacitor is
recommended between the input and ground to prevent oscilla-
tion.
where T
A
is the maximum ambient temperature in
°C,
I
O
is the maximum output (load) current in amperes, and
V
I
is the maximum input voltage in volts.
The following graph gives the required copper foil area
(soldered to leads 7 and 8) to provide the required thermal
resistance. Note that more is always better and both sides of the
printed wiring board can be used.
ENABLE input.
The ENABLE input includes an internal pull-
2000
GLASS-EPOXY
PRINTED WIRING BOARD
1000
FOIL AREA in SQ. mm
500
300
200
100
90
100
110
120
130
Dwg. GK-031
JUNCTION-TO-AMBIENT THERMAL RESISTANCE in
°
C/W
6
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
TM
ALLEGRO [ ALLEGRO MICROSYSTEMS ]
