MC33341
http://onsemi.com
7
Pin 8 to ground. This configuration is shown for ease of
understanding and would normally be used to provide an
isolated control signal to a primary side switching regulator
controller. In non−isolated, primary or secondary side
applications, a load resistor can be placed from Pin 8 to
ground. This resistor will convert the Drive Output current
to a voltage for direct control of a regulator.
In applications where excessively high peak currents are
possible from the source or load, the load induced voltage
drop across R
S
could exceed 1.6 V. Depending upon the
current sensing configuration used, this will result in
forward biasing of either the internal V
CC
clamp diode,
Pin 6, or the device substrate, Pin 1. Under these conditions,
input series resistor R3 is required. The peak input current
should be limited to 20 mA. Excessively large values for R3
will degrade the current sensing accuracy. Figure 22 shows
a method of bounding the voltage drop across R
S
without
sacrificing current sensing accuracy.
Figure 14. Source High−Side Current Sensing with
Internally Fixed Voltage and Current Thresholds
R
S
Load
R1
Battery or
Resistive
Load
Source
Return
Source
R2
R3
Comp
The above figure shows the MC33341 configured for source high−side current sensing allowing a common ground path between Load − and
Source Return −. The Differential Amplifier inputs, Pins 1 and 6, are used to sense the load induced voltage drop that appears across resisto
R
S
. The internal voltage and current regulation thresholds are selected by the respective external connections of Pins 2 and 6. Resistor R3
is required in applications where a high peak level of reverse current is possible if the source inputs are shorted. The resistor value should
be chosen to limit the input current of the internal V
CC
clamp diode to less than 20 mA. Excessively large values for R3 will degrade the
current sensing accuracy.
V
reg
+ V
th(V)
ǒ
R2
R1
) 1
Ǔ
+ 1.2
ǒ
R2
R1
) 1
Ǔ
I
reg
+
V
th(IHS)
R
S
+
0.2
R
S
R3 +
ǒ
I
pk
R
S
Ǔ
–0.6
0.02
V
I
Load
8765
1234
R
R
R
R
R
V
CC
V
CC
V
CC
V
CC
V
CC
V
CC
0.4 V
1.2 V
R
0.2 V
V
CC
0.2 V 0.4 V 1.2 V
V
CC
1.2 V
V
CC
Inverting Amp
Transconductance
Amp
Differential Amp
Disable Logic
Differential Amp
Opto
Isolator
V
sen
V
th
I
sen
I
th
Reference
