ISL78307_15 Datasheet, PDF (7/9 Pages) Intersil Corporation – 40V, Low Quiescent Current, 50mA Linear Regulator for Automotive Applications

ISL78307
Functional Description
Functional Overview
The ISL78307 is a high performance, high voltage, low-dropout
regulator (LDO) with 50mA 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 ISL78307 features an enable pin. When it is pulled low, the
IC goes to a shutdown mode. In this condition, the device draws
less than 2µA. Driving the pin high turns the device on.
Current Limit Protection
The ISL78307 has internal current limit 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 the die temperature exceeds typically +165°C, the
output of the LDO will shut down until the die temperature cools
down to typically +145°C. The level of power dissipated,
combined with the ambient temperature and the thermal
impedance of the package, will determine if the junction
temperature exceeds the thermal shutdown temperature. See
section on “Power Dissipation”.
Application Information
Input and Output Capacitors
For the output, a ceramic capacitor (X5R or X7R) with a
capacitance of 10µF is recommended for the ISL78307 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. A minimum of 0.1µF (X5R or X7R) is
recommended at the input.
Output Voltage Setting
For the adjustable version of the ISL78307, the output voltage is
programmed using an external resistor divider as shown in
Figure 12.
CIN
0.1µF
IN
OUT
R1
EN
ADJ
(ISL78307)
R2
GND
COUT
10µF
FIGURE 12. ADJUSTABLE VERSION
The output voltage is calculated using Equation 1:
V_OUT
=
1.223 V




R^-R----12-
+
1

(EQ. 1)
Power Dissipation
The junction temperature must not exceed the range specified in
“Recommended Operating Conditions” on page 3. The power
dissipation can be calculated using Equation 2:
P_D = V_IN – V_OUT  I_OUT + V_IN  I_GND
(EQ. 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:
T_J = T_{JMAX} – T_{AMAX}
(EQ. 3)
To calculate the maximum ambient operating temperature, use
the junction-to-ambient thermal resistance (_JA) as shown in
Equation 4:
T_{JMAX} = P_{DMAX} x _JA + T_A
(EQ. 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.
Connect EPAD to the ground plane for better heat dissipation.
Thermal vias on the EPAD increase heat dissipation.
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FN7658.3
April 7, 2015