AOZ1320
Detailed Description
Slew Rate Control
The AOZ1320 is a family of P-channel high-side load
switches with controlled slew rate. The device is enabled
when the input voltage is above the Under-Voltage
Lockout (UVLO) threshold and the EN pin is high. Once
enabled, the gate driver and slew-rate control circuitry
immediately raises the source-to-gate voltage of the
P-channel MOSFET to its threshold level, and then
gradually turns on the MOSFET by linearly increases the
source-to-gate voltage. This slow turn-on action
effectively limits the input inrush current and provides
a nice ramp for the output voltage. After the MOSFET is
fully enhanced, the AOZ1320 quickly increases the
source-to-gate voltage to the full input voltage to
minimize on resistance and reduce power dissipation.
Three slew-rate options are available. AOZ1320-01
and -04 have a slew rate of 1ms, and the AOZ1320-07
has a slew rate of 4.5ms. This option significantly reduces
the inrush current when the MOSFET turns on, allowing
the use of very small input capacitor. AOZ1320-02 and
-05 have no slew rate control and the MOSFET can be
turned on within 500ns. This option is suitable for
applications that require very fast switching. AOZ1320-03
and -06 have a moderate slew rate to 100µs. The
AOZ1320-03, -04, -05, and -07 options include an
internal output discharge circuit that quickly discharges
the output to ground when the device is disabled.
Input Under-Voltage Lockout
The operating voltage range of AOZ1320 is from 1.8V
to 5.5V. An internal UVLO comparator monitors the input
voltage. The device is disabled if the input voltage falls
below the UVLO threshold (0.9V typical). The UVLO
comparator has about 300mV hysteresis.
On/Off Control
The AOZ1320 is enabled when the input voltage is above
the UVLO threshold and the EN pin is asserted high.
The device is disabled when the input voltage is below
the UVLO threshold or the EN pin is asserted low. The
EN input is compatible with both TTL and CMOS logic.
Internal Discharge Resistor
The AOZ1320 has an internal 180Ω resistor to discharge
any remaining voltage from the system to the ground
that is store in a capacitive load. This provides a safe
shutdown of the system to prevent any damages to the
devices. This function is controlled from the Enable pin.
Applications Information
Input Capacitor Selection
Use a 1µF or larger capacitor for input bypassing.
Place the capacitor close to the IN pins of AOZ1320.
Output Capacitor Selection
Use a 0.1µF or larger capacitor between OUT and GND.
The capacitance does not affect the turn-on slew rate.
However, a larger capacitor makes the initial turn-on
transient smoother.
Thermal Considerations
To ensure proper operation, the maximum junction
temperature (T
J(MAX)
) of AOZ1320 should not exceed
150°C. Several factors attribute to the junction temperature
rise: load current, MOSFET on resistance (R
DS(ON)
), on-
resistance temperature coefficient (T
C
), junction-to-ambient
thermal resistance (Θ
JA
), and ambient temperature (T
A
).
Use the following equation to determine the maximum
continuous load current I
LOAD(MAX)
:
I
LOAD
(
MAX
)
=
T
J
(
MAX
)
–
T
A
-------------------------------------------------------------------------------------------------------------------
-
Θ
JA
•
R
DS
(
ON
)
• [
1
+
T
C
• (
T
J
(
MAX
)
–
T
A
) ]
Rev. 1.6 August 2008
where
R
DS(ON)
is the maximum value of the MOSFET on
resistance at 25°C. Please note the maximum load current
should not exceed the absolute maximum current rating of
the switch. For the SOT-23 package, the absolute maxi-
mum current rating is 1.6A. For the 2x2 DFN package, the
absolute maximum current rating is 2.3A.
For example, when V
IN
= 5V, the maximum continuous
load current of SOT-23 package at room temperature is:
I
LOAD
(
MAX
)
=
150°C
–
25°C
---------------------------------------------------------------------------------------------------------------------------------------------
=
2.78A
-
120°C
⁄
W
•
100mΩ
• [
1
+
0.0028
• (
150°C
–
25°C
) ]
Since the calculated current is greater than the absolute
maximum current rating, the maximum load current at
V
IN
= 5V and room temperature is 1.6A.
Exceeding the maximum continuous load current may
cause damage to the device. Figure 3 and Figure 4 show
the maximum load current as a function of the ambient
temperature for SOT23 and 2x2 DFN packages respec-
tively. To ensure proper operation, the load current should
not exceed the limits in these two figures.
Page 11 of 18
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