LT1089_15 Datasheet, PDF (5/8 Pages) Linear Technology – High Side Switch

TYPICAL APPLICATIO S
Driving Ground Referred Loads
12V
Driving Negative Referred Loads
12V
LT1089
Driving Inductive Loads
12V
LOGIC
IN
LT1089
V_OUT
LT1089 • TA01
LOGIC
IN
LT1089
V_OUT
–5V
LT1089 • TA02
LOGIC
IN
LT1089
20V
V_OUT
LT1089 • TA03
UU
APPLICATIO HI TS
The logic and ground pins function as a differential logic
input with a common-mode range of V_CC to V_CC – 20V and
a differential threshold voltage (V_LOGIC – GND) of 1.5V.
Note that if either Logic In or GND are left open the switch
remains inactive.
The LT1089 must be protected against overvoltage at
turn-off when driving inductive loads. The inductive flyback
voltage can easily exceed the maximum operating switch
voltage (V_CC – V_OUT) of 20V, potentially damaging the
switch. The solution is to clamp the switch voltage to 20V
or less with a zener diode. Remember that the switch can
handle 7.5A and the Zener may be required to handle the
same amount of current.
Care must be exercised when operating near the
maximum switch voltage. A high current or capacitive load
may trip the current limit circuit at turn-on, thereby
adversely affecting the risetime of V_OUT. The risetime is
then governed by the current limit divided by the load
capacitance, while the falltime is a function of the complex
load. In addition, at switch voltages greater than 18V
the switch current must be less than 0.5A or the device
output will not pull up. Check the short circuit current
characteristics for more detailed information.
1089fa
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