LTM8001 Datasheet, PDF (17/28 Pages) Linear Technology – de36VIN, 5A μModule Regulator with 5-Output Configurable LDO Array

LTM8001
APPLICATIONS INFORMATION
event. The SCR latches when the input voltage threshold
is exceeded, so this circuit should be used with a fuse, as
shown, or employ some other method to interrupt current
from the load.
As mentioned, the LTM8001 sinks current by energy
conversion and not dissipation. Thus, no matter what
protection circuit that is used, the amount of power that the
protection circuit must absorb depends upon the amount
of power at the input. For example, if the output voltage is
2.5V and can sink 5A, the input protection circuit should
be designed to absorb at least 7.5W. In Figures 5a and 5b,
let us say that the protection activation threshold is 30V.
Then the circuit must be designed to be able to dissipate
7.5W and accept 7.5W/30V = 250mA.
Figures 5a through 5c are crowbar circuits, which attempt
to prevent the input voltage from rising above some level
by clamping the input to GND through a power device. In
some cases, it is possible to simply turn off the LTM8001
when the input voltage exceeds some threshold. This
is possible when the voltage power source that drives
current into V_OUT never exceeds V_IN. An example of this
circuit is shown in Figure 5d. When the power source on
the output drives V_IN above a predetermined threshold,
the comparator pulls down on the RUN pin and stops
switching in the LTM8001. When this happens, the input
capacitance needs to absorb the energy stored within the
LTM8001’s internal inductor, resulting in an additional
voltage rise. As shown in the Block Diagram, the internal
LOAD
CURRENT
V_IN
V_OUT0
ZENER
DIODE
LTM8001
Q
GND
SOURCING
LOAD
R
8001 F05a
Figure 5a. The MOSFET Q Dissipates Momentary Energy to
GND. The Zener Diode and Resistor Are Chosen to Ensure That
the MOSFET Turns On Above the Maximum V_IN Voltage Under
Normal Operation
LOAD
CURRENT
V_IN
V_OUT0
ZENER
SCR
DIODE
LTM8001
GND
FUSE
SOURCING
LOAD
8001 F05a
Figure 5c. The SCR Latches On When the Activation Threshold is
Reached, So a Fuse or Some Other Method of Disconnecting the
Load Should be Used
OPTIONAL
HYSTERESIS
RESISTOR
Q
V_IN
V_OUT0
LTM8001
V_{REF GND}
LOAD
CURRENT
SOURCING
LOAD
8001 F05b
Figure 5b. The Comparator in This Circuit Activates the Q
MOSFET at a More Precise Voltage Than the One Shown in
Figure 5a. The Reference for the Comparator is Derived from
the V_REF Pin of the LTM8001
V_IN
V_OUT0
LTM8001
LOAD
CURRENT
RUN
GND
SOURCING
LOAD
10µF
–
+
EXTERNAL
REFERENCE
VOLTAGE
8001 F05d
Figure 5d. This Comparator Circuit Turns Off the LTM8001 if
the Input Rises Above a Predetermined Threshold. When the
LTM8001 Turns Off, the Energy Stored in the Internal Inductor
Will Raise V_IN a Small Amount Above the Threshold.
For more information www.linear.com/8001
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