SiP32451, SiP32452, SiP32453
Vishay Siliconix
Document Number: 63315
S12-2345-Rev. D, 8-Oct-12
www.vishay.com
9
This document is subject to change without notice.
THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000
For technical questions, contact: powerictechsupport@vishay.com
DETAILED DESCRIPTION
SiP32451, SiP32452 and SiP32453 are n-channel power
MOSFET designed as high side load switch. Once enable
the device charge pumps the gate of the power MOSFET to
a constant gate to source voltage for fast turn on time. The
mostly constant gate to source voltage keeps the on
resistance low through out the input voltage range. When
disable, the SiP32451 and SiP32452 pull the gate of the
output n-channel low right away for a fast turn off delay while
there is a build-in turn off delay for the SiP32453. The
SiP32451 especially features a output discharge circuit to
help discharge the output capacitor. The turn off delay for the
SiP32453 is guaranteed to be at least 30 µs. Because the
body of the output n-channel is always connected to GND, it
prevents the current from going back to the input in case the
output voltage is higher than the output.
APPLICATION INFORMATION
Input Capacitor
While a bypass capacitor on the input is not required,
a 4.7 µF or larger capacitor for C
IN
is recommended in almost
all applications. The bypass capacitor should be placed as
physically close as possible to the input pin to be effective in
minimizing transients on the input. Ceramic capacitors are
recommended over tantalum because of their ability to
withstand input current surges from low impedance sources
such as batteries in portable devices.
Output Capacitor
A 0.1 µF capacitor across V
OUT
and GND is recommended
to insure proper slew operation. There is inrush current
through the output MOSFET and the magnitude of the inrush
current depends on the output capacitor, the bigger the C
OUT
the higher the inrush current. There are no ESR or capacitor
type requirement.
Enable
The EN pin is compatible with CMOS logic voltage levels. It
requires at least 0.1 V or below to fully shut down the device
and 1.5 V or above to fully turn on the device.
Protection Against Reverse Voltage Condition
SiP32451, SiP32452 and SiP32453 can block the output
current from going to the input in case where the output
voltage is higher than the input voltage when the main switch
is off.
Thermal Considerations
These devices are designed to maintain a constant output
load current. Due to physical limitations of the layout and
assembly of the device the maximum switch current is 1.2 A
as stated in the Absolute Maximum Ratings table. However,
another limiting characteristic for the safe operating load
current is the thermal power dissipation of the package. To
obtain the highest power dissipation (and a thermal
resistance of 280 °C/W) the device should be connected to a
heat sink on the printed circuit board.
The maximum power dissipation in any application is
dependant on the maximum junction temperature,
T
J(max.)
= 125 °C, the junction-to-ambient thermal resistance,
J-A
= 280 °C/W, and the ambient temperature, T
A
, which
may be formulaically expressed as:
It then follows that, assuming an ambient temperature of
70 °C, the maximum power dissipation will be limited to about
196 mW.
So long as the load current is below the 1.2 A limit, the
maximum continuous switch current becomes a function two
things: the package power dissipation and the R
DS(ON)
at the
ambient temperature.
As an example let us calculate the worst case maximum load
current at T
A
= 70 °C. The worst case R
DS(ON)
at 25 °C is
65 m. The R
DS(ON
) at 70 °C can be extrapolated from this
data using the following formula:
R
DS(ON)
(at 70 °C) = R
DS(ON)
(at 25 °C) x (1 + T
C
x T)
Where T
C
is 3900 ppm/°C. Continuing with the calculation
we have
R
DS(ON)
(at 70 °C) = 65 m x (1 + 0.0039 x (70 °C - 25 °C))
= 76.4 m
The maximum current limit is then determined by
which in this case is 1.6 A. Under the stated input voltage
condition, if the 1.6 A current limit is exceeded the internal die
temperature will rise and eventually, possibly damage the
device.
To avoid possible permanent damage to the device and keep
a reasonable design margin, it is recommended to operate
the device maximum up to 1.2 A only as listed in the
Absolute Maximum Ratings table.
280
125
(max.)
(max.)
A
A
J
A
J
T
TT
P
-
=
-
=
-
θ
) (
(max.)
(max.)
ON DS
LOAD
R
P
I <
