SiP32411
Vishay Siliconix
Document Number: 66710
S11-1694-Rev. E, 22-Aug-11
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
DETAILED DESCRIPTION
SiP32411 is an n-channel power MOSFET designed as high
side load switch with slew rate control to prevent in-rush
current. Once enable the device charge pumps the gate of
the power MOSFET to 5 V gate to source voltage while
controlling the slew rate of the turn on time. The mostly
constant gate to source voltage keeps the on resistance low
through out the input voltage range. When disable, the
output discharge circuit turns on to help pull the output
voltage to ground more quickly. Also in disable mode, the
reverse blocking circuit is activated to prevent current from
going back to the input in case the output voltage is higher
than the input voltage. Input voltage is needed for the reverse
blocking circuit to work properly, it can be as low as V
IN(min)
.
APPLICATION INFORMATION
Input Capacitor
While a bypass capacitor on the input is not required,
a 2.2 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 SiP32411 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 or larger across V
OUT
and GND is
recommended to insure proper slew operation. C
OUT
may be
increased without limit to accommodate any load transient
condition with only minimal affect on the SiP32411 turn on
slew rate time. There are no ESR or capacitor type
requirement.
Enable
The EN pin is compatible with both TTL and CMOS logic
voltage levels.
Protection Against Reverse Voltage Condition
The SiP32411 contains a reverse blocking circuitry to protect
the current from going to the input from the output in case
where the output voltage is higher than the input voltage
when the main switch is off. A supply voltage as low as the
minimum required input voltage is necessary for this circuitry
to work properly.
Thermal Considerations
The SiP32411 is 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 1.8 A
for SC70-6 package and 2.4 A for TDFN4 package, 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
240 °C/W for SC70-6 and 170 °C/W for TDFN4) the power
pad of 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
for the TDFN4 1.2 mm x 1.6 mm package,
J-A
= 170 °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
324 mW.
So long as the load current is below the 2.4 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
occurs at an input voltage of 1.2 V and is equal to 75 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 3400 ppm/°C. Continuing with the calculation
we have
R
DS(ON)
(at 70 °C) = 75 m x (1 + 0.0034 x (70 °C - 25 °C))
= 86.5 m
The maximum current limit is then determined by
which in case is 1.94 A. Under the stated input voltage
condition, if the 1.94 A current limit is exceeded the internal
die temperature will rise and eventually, possibly damage the
device.
Vishay Siliconix maintains worldwide manufacturing capability. Products may be manufactured at one of several qualified locations. Reliability data for Silicon
Technology and Package Reliability represent a composite of all qualified locations. For related documents such as package/tape drawings, part marking, and
reliability data, see www.vishay.com/ppg?66710
.
170
125
(max.)
(max.)
A
A
J
A
J
T
TT
P
-
=
-
=
-
θ
) (
(max.)
(max.)
ON DS
LOAD
R
P
I <
