Intersil Corporation CA3274 Datasheet
April 1994
CA3274
Current Limiting Power Switch
with Current Limiter Sense Flag
Features
• Drive-Current Limiting at Output
• Current-Sense Buffer and Reference
• 200mA Driver Current Capability
• Logic-Level Control Input
• Current Limiting Flag Output
• 50dB Minimum PSRR
•5µs Typical Switch Time
• Separate Signal and Power Grounds
Applications
• Solenoid Switch Driver
• Relay Driver
• Lamp Control Switch
• Ignition Coil Pre-Driver
• Constant Current Driver
• Current Limiting Switch
• Fault Output Sense Appliance
• Power Supply Fault Mode Control
Ordering Information
TEMPERATURE
PART NUMBER
CA3274E -40oC to +85oC 8 Lead Plastic DIP
RANGE PACKAGE
Description
The CA3274 is a controlled current switch and may be used in
general purpose switching applications that require specified
maximum levels of current. The functional block diagram of
the CA3274 is shown and a typical application circuit is shown
in Figure 1. An internal emitter follower has 200mA of source
drive output capability. The Control Input is a Schmitt trigger
buffer amplifier for noise immunity in the environments typical
of industrial and automotive control systems.
Current sensing in the emitter circuit of a power-darlington
output stage is fed back from a sampling resistor to the sense
input of the CA3274 which has a 335mV typical offset. For the
example shown in Figure 1, a sampling resistor of 0.056Ω
permits 6.0A (0.335/0.056) of current in the emitter of the output
driver. When the current limiter is activated, the flag output
changes state conditionally. If the control input is the “0” state,
the flag output will remain in a “1” state. If the control input is in
the “1” state and the sense input is less than the voltage
reference level of 335mV, the flag output will remain in the “1”
state. If the control input is the “1” state and the sense input is
equal to or greater than the 335mV reference level, the flag
output goes to the “0” state. The output flag switch may be used
to accurately establish dwell timing in automotive applications.
When the control input goes to “0”, the flag is reset to “1”. Noiseimmunity hold-off is used to prevent pre-triggering of the flag
output and is noted as t
The flag output may be used for diagnostic feedback via the
current sense input to detect a fault mode. In this case the
sampled drive current is either from the emitter of the CA3274
internal power transistor or an external output amplifier, such as
a darlington power transistor or power-FET output stage. The
CA3274 has separate power and signal grounds to minimize
transient-loop feedback to the input ground and thus prevent
false triggering of the output. Optionally, the output from the
CA3274 may be taken from the open collector (DRIVE IN) at
pin 6. An external resistor at pin 6 may be used to set the level
at which Q2 will saturate, providing additional limiting protection
for the maximum forward-drive from the CA3274.
in the timing diagram of Figure 2.
D
Pinout
CA3274 (PDIP)
TOP VIEW
FLAG OUT
SENSE IN
POWER GND
SIGNAL GND
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
http://www.intersil.com or 407-727-9207
| Copyright © Intersil Corporation 1999
1
2
3
4
10-40
VCC SUPPLY
8
7
CONTROL IN
6
DRIVE IN
5
DRIVE OUT
File Number 2222.2
Block Diagram
V
CC
8
CA3274
CONTROL
FLAG
OUT
SIGNAL
GROUND
D1 R4
7
IN
1
Q1
4
LATCH
CONTROL
LOGIC AND
CURRENT
LIMITER
3
Q2
-
SENSE
+
335mV
POWER
GROUND
6
DRIVE IN
5
2
IN
DRIVE OUT
R2
RELAY OR
SOLENOID LOAD
R3
SENSE
R1
CONTROL
FLAG
OUT
SIGNAL
GROUND
V
CC
8
7
IN
1
Q1
4
LATCH
CONTROL
LOGIC &
CURRENT
LIMITER
3
Q2
DRIVE
-
SENSE
+
335mV
POWER
GROUND
6
5
DARLINGTON
2
IN
V
CC1
LOAD
6A
0.056Ω
SENSE LEVEL EQUALS
335mV
= 6A
0.056Ω
FIGURE 1. TYPICAL APPLICATION AS A POWER SWITCH PRE-DRIVER SWITCH
10-41
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