LMD18400 Datasheet, PDF (9/26 Pages) National Semiconductor (TI) – Quad High Side Driver

LMD18400
www.ti.com
APPLICATIONS INFORMATION
SNVS094C – JUNE 1996 – REVISED APRIL 2013
BASIC OPERATION
High-side drivers are used extensively in automotive and industrial applications to switch power to ground
referred loads. The major advantage of using high-side drive, as opposed to low-side drive, is to protect the load
from being energized in the event that the load drive wire is inadvertently shorted to ground as shown in
Figure 18. A high-side driver can sense a shorted condition and open the power switch to disable the load and
eliminate the excessive current drain on the power supply. The LMD18400 can control and protect up to four
separate ground referenced loads.
Figure 18. High-Side vs Low-Side Drive
The LMD18400 combines low voltage CMOS logic control circuitry with a high voltage DMOS process. Each
DMOS power switch has an individual ON/OFF control input. When commanded ON, the output of the switch will
connect the load to the V_CC supply through a maximum resistance of 1.3Ω (the ON resistance of the DMOS
switch). The voltage applied to the load will depend upon the load current and the designed current capability of
the LMD18400. When a switch is commanded OFF, the load will be disconnected from the supply except for a
small leakage current of typically less than 0.01 µA.
The LMD18400 can be continually connected to a live power source, a car battery for example, while drawing
less than 10 µA from the power source when put into a “sleep” condition. This “sleep” mode is enacted by taking
the Enable Input (pin 3) low. During this mode the supply current for the device is typically only 0.04 µA. Special
low current consumption standby circuitry is used to hold the DMOS switches OFF to eliminate the possibility of
supply voltage transients from turning on any of the loads (a common problem with MOS power devices). When
in the “sleep” mode, all diagnostic and logic circuitry is inactive. When the Enable Input is taken to a logic 1, the
switches become “armed” and ready to respond to their control input after a short, 30 µs, enable delay time. This
delay interval prevents the switches from transient turn-on. Figure 19 shows the switch control logic.
Copyright © 1996–2013, Texas Instruments Incorporated
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