ISL78301
8
FN6705.2
April 7, 2015
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Functional Description
Functional Overview
The ISL78301 is a high performance, high voltage, low-dropout
regulator (LDO) with 150mA sourcing capability. The part is
qualified to operate over the -40°C to +125°C automotive
temperature range. Featuring ultra-low quiescent current, it
makes an ideal choice for “always-on” automotive applications. It
works well under a “load-dump condition” where the input
voltage could rise up to 40V. The LDO continues to operate down
to 3V under a “cold-crank” condition. The device also features
current limit and thermal shutdown protection.
Enable Control
The ISL78301 has an enable pin which turns the device on when
pulled high. When EN is low, the IC goes into shutdown mode and
draws less than 2µA.
Current Limit Protection
The ISL78301 has internal current limiting functionality to
protect the regulator during fault conditions. During current limit,
the output sources a fixed amount of current largely independent
of the output voltage. If the short or overload is removed from
V
OUT
, the output returns to normal voltage regulation mode.
Thermal Fault Protection
In the event that the die temperature exceeds a typical value of
+165°C, the output of the LDO will shut down until the die
temperature cools down to a typical +145°C. The level of power
dissipated, combined with the ambient temperature and the
thermal impedance of the package, determines if the junction
temperature exceeds the thermal shutdown temperature. See
“
Power Dissipation” for more details.
Application Information
Input and Output Capacitors
A minimum 0.1µF ceramic capacitor is recommended at the
input for proper operation. For the output, a ceramic capacitor
with a capacitance of 10µF is recommended for the ISL78301 to
maintain stability. The ground connection of the output capacitor
should be routed directly to the GND pin of the device and also
placed close to the IC.
Output Voltage Setting
For the adjustable version of the ISL78301, the output voltage is
programmed using an external resistor divider as shown in
Figure 12
.
The output voltage is calculated using Equation 1
:
Power Dissipation
The junction temperature must not exceed the range specified in
“
Recommended Operating Conditions” on page 4. The power
dissipation can be calculated using Equation 2:
The maximum allowable junction temperature, T
J(MAX)
and the
maximum expected ambient temperature, T
A(MAX)
will determine
the maximum allowable junction temperature rise (T
J
), as shown
in Equation 3:
To calculate the maximum ambient operating temperature, use
the junction-to-ambient thermal resistance (
JA
) as shown in
Equation 4
:
Board Layout Recommendations
A good PCB layout is important to achieve expected
performance. Consideration should be taken when placing the
components and routing the trace to minimize the ground
impedance and keep the parasitic inductance low. The input and
output capacitors should have a good ground connection and be
placed as close to the IC as possible. The feedback trace in the
adjustable version should be away from other noisy traces.
The 14 Ld HTSSOP package uses the copper area on the PCB as
a heatsink. The EPAD of this package must be soldered to the
copper plane (GND plane) for effective heat dissipation.
Figure 13
shows a curve for
JA
of the package for different
copper area sizes.
IN
OUT
EN
(ISL78301)
ADJ
GND
C
IN
0.1µF
C
OUT
10µF
R1
R2
FIGURE 12. ADJUSTABLE VERSION
V
OUT
1.223V
R
1
R
2
-------
1+
=
(EQ. 1)
P
D
V
IN
V
OUT
–I
OUT
V
IN
I
GND
+=
(EQ. 2)
T
J
T
JMAX
T
AMAX
–=
(EQ. 3)
T
JMAX
P
DMAX
x
JA
T
A
+=
(EQ. 4)
FIGURE 13.
JA
vs EPAD-MOUNT COPPER LAND AREA ON PCB
38
36
34
32
30
28
26
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160
EPAD-MOUNT COPPER LAND AREA ON PCB, mm
2
THETA-JA, C/W
