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© 2011 Fairchild Semiconductor Corporation www.fairchildsemi.com
Rev. 1.0.1 • 2/13/12
AN-8039
Using the FDDS100H06_F085 in Automotive Systems
Background
Smart high-side switches are a standard building block in
today’s automotive power distribution and electrical control
systems. High and medium current devices with diagnostic
features have virtually eliminated fuses and resettable
breakers in load management.
In power distribution, single circuits and the associated
wiring are protected using smart high-side switches. In
body, lighting, and power train; individual loads are driven
with smart devices that may include diagnostics using
current sensing, and/or fixed parameter diagnostics with
status feedback, and/or self-protection features.
Autonomous self-protection is almost universal.
Medium Power Load Management
The FDDS100H06_F085 is an AECQ101-grade, smart,
high-side switch designed to drive medium power electrical
loads and provide diagnostic feedback with a
microprocessor-compatible logic level interface. This
includes fixed limits for open-load, over-current, and other
failure conditions indicated via a status line. There are also
autonomous self-protection functions to prevent damage to
the device for conditions such as over temperature, shorted
load, load dump, and over-voltage.
Overview
Physical Construction
The FDDS100H06_F085 is monolithic (single silicon IC)
design, packaged in a 5-lead DPak. The center lead, pin 3, is
trimmed and not used to contact the PCB. The TAB is
electrically common with pin 3. The package drawing is
included in the datasheet.
Table 1. Pin Definitions
Pin # Name I/O Description
1 GND P
Ground
2 IN A
Input; activates the power switch in
case of logic HIGH
3 VBB P
Supply voltage; pin 3 and TAB are
internally shorted.
4 ST A
Fault signal feedback LOW on failure
5 OUT A
Output to loads
Pin Functions
IN - The input pin can be driven with a 3V to 5V logic level
output from devices like microcontrollers, provided the V
OH
output at 3V conforms to the V
OHmin
> 2.9V as specified for
typical HC logic families (see example V
OH
minimum for the
74VHC00).
ST - The status output is an open-drain configuration and
requires a pull-up resistor. This allows multiple devices to
be wire OR’ed where multiple loads do not require
individual diagnostic recognition. Open-load detection can
still be accomplished individually by polling of the input
and status pins.
The output minimum voltage specified on the status pin
relates to the Zener protection diode and is compatible with
3V to 5V logic levels. This should be pulled up to the logic
V
CC
voltage.
VBB – The tab and pin 3 are electrically common; however,
pin 3 is a cut lead and not used for electrical connection.
Therefore, power for the device must be provided at the tab.
The tab pad can also be used with thermal vias and
additional PCB radiation area for heat dissipation.
OUT – The output pin is connected to the source of the
embedded N-channel MOSFET to source current to the
load. The OUT pin is sensed internally for open-load and
short-circuit protections.
GND – The ground circuit does not have a large current as
it is used only for the internal logic. The ground pin may
require added protection for reverse battery, per Section 6.
Figure 1. Block Diagram
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