MC3423D ON Semiconductor, MC3423D Datasheet - Page 4

• Manufacturer Part Number: MC3423D
• Description: IC SENSOR UNDERVOLTAGE 8SOIC
• Manufacturer: ON Semiconductor
• Series: MC3423r

Specifications of MC3423D

• Technology: Mixed Technology
• Number Of Circuits: 2
• Applications: General Purpose
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power (watts): -
• Voltage - Working: -
• Voltage - Clamping: -
• Other names: MC3423DOS

Basic Circuit Configuration
shown in Figure 3 for supply voltages from 4.5 V to 36 V,
and in Figure 4 for trip voltages above 36 V. The threshold
or trip voltage at which the MC3423 will trigger and supply
gate drive to the crowbar SCR, Q1, is determined by the
selection of R1 and R2. Their values can be determined by
the equation given in Figures 3 and 4, or by the graph shown
in Figure 8. The minimum value of the gate current limiting
resistor, R
SCR, Q1, will receive the greatest gate current possible
without damaging the MC3423. If lower output currents
are required, R
shown in Figure 3 may be used to reset the crowbar.
Otherwise, the power supply, across which the SCR is
connected, must be shut down to reset the crowbar. If a non
current−limited supply is used, a fuse or circuit breaker, F1,
should be used to protect the SCR and/or the load.
have a typical propagating delay of 1.0 ms. If faster
operation is desired, Pin 3 may be connected to Pin 2 with
Pin 4 left floating. This will result in decreasing the
propagating delay to approximately 0.5 ms at the expense
of a slightly increased TC for the trip voltage value.
Configuration for Programmable Minimum Duration
of Overvoltage Condition Before Tripping
noise environment. To prevent false tripping of the OVP
circuit by noise which would not normally harm the load,
MC3423 has a programmable delay feature. To implement
this feature, the circuit configuration of Figure 5 is used. In
this configuration, a capacitor is connected from Pin 3 to
V
duration of the overvoltage condition which is necessary to
trip the OVP. The value of C can be found from Figure 10.
The circuit operates in the following manner: When V
rises above the trip point set by R1 and R2, an internal
current source (Pin 4) begins charging the capacitor, C,
connected to Pin 3. If the overvoltage condition disappears
before this occurs, the capacitor is discharged at a rate 10
times faster than the charging rate, resetting the timing
feature until the next overvoltage condition occurs.
the supply occur when a high overvoltage condition occurs,
while retaining the false tripping immunity of Figure 5. In
this case, the circuit of Figure 6 can be used. The circuit will
operate as previously described for small overvoltages, but
will immediately trip if the power supply voltage exceeds
V
EE
Z1
The basic circuit configuration of the MC3423 OVP is
The circuit configurations shown in Figures 3 and 4 will
In many instances, the MC3423 OVP will be used in a
Occasionally, it is desired that immediate crowbarring of
. The value of this capacitor determines the minimum
+ 1.4 V.
G
, is given in Figure 9. Using this value of R
G
can be increased in value. The switch, S1,
APPLICATION INFORMATION
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G
, the
CC
MC3423
4
Additional Features
1. Activation Indication Output
2. Remote Activation Input
activation is provided by the MC3423. This output is an
open collector transistor which saturates when the OVP
is activated. In addition, it can be used to clock an edge
triggered flip−flop whose output inhibits or shuts down
the power supply when the OVP trips. This reduces or
eliminates the heatsinking requirements for the crowbar
SCR.
activation input, Pin 5. If the voltage on this CMOS/TTL
compatible input is held below 0.8 V, the MC3423
operates normally. However, if it is raised to a voltage
above 2.0 V, the OVP output is activated independent of
whether or not an overvoltage condition is present. It
should be noted that Pin 5 has an internal pullup current
source. This feature can be used to accomplish an
orderly and sequenced shutdown of system power
supplies during a system fault condition. In addition, the
activation indication output of one MC3423 can be used
to activate another MC3423 if a single transistor inverter
is used to interface the former’s indication output to the
latter ’s remote activation input, as shown in Figure 7. In
this circuit, the indication output (Pin 6) of the MC3423
on power supply 1 is used to activate the MC3423
associated with power supply 2. Q1 is any small PNP
with adequate voltage rating.
Supply
Power
An additional output for use as an indicator of OVP
Another feature of the MC3423 is its remote
Figure 7. Configuration for Programmable
Duration of Overvoltage Condition Before
Z1
Trip/With Immediate Trip at
High Overvoltages
(+ Sense
R1
R2
Lead)
1k
2
5
4
3
MC3423
C
1
7
(− Sense Lead)
8
R
G
+
−