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PRODUCT SPECIFICATION
RC5040
15
Table 7. Comparison of Sense Resistors
1
Notes:
1. Refer to Appendix A for Directory of component suppliers
Description
Tolerance
Factor (TF)
Size
(L x W x H)
Power capability >50A/in
Motherboard
Trace Resistor
±
29%
Discrete Iron
Alloy
resistor (IRC)
±
5%
(
±
1% available)
0.45" x 0.065" x
0.200"
1 watt
(3W and 5W
available)
+30 ppm
Discrete Metal
Strip surface
mount resistor
(Dale)
±
1%
Discrete MnCu
Alloy wire
resistor
±
10%
Discrete
CuNi Alloy
wire resistor
(Copel)
±
10%
2" x 0.2" x 0.001"
(1 oz Cu trace)
0.25" x 0.125" x
0.025"
1 watt
0.200" x 0.04" x
0.160"
1 watt
0.200" x 0.04" x
0.100"
1 watt
Temperature
Coefficient
Cost
@10,000 piece
+4,000 ppm
±
75 ppm
±
30 ppm
±
20 ppm
Low
included in
motherboard
$0.31
$0.47
$0.09
$0.09
Based on the Tolerance in the above table,
For Embedded PC Trace Resistor
and for
I
l
oad,max
=14.5A
:
For discrete resistor
and I
load, max
= 14.5A
:
For user convenience, Table 8 lists recommended Value for
sense resistor for various load current using Embedded PC
Trace Resistor or Discrete Resistor.
R
SENSE
V
I
Load, max
+
1.0A
----------------------------------------
1
TF
–
(
)
′
=
=
1.0A
14.5A
+
------100mV
1
29%
–
(
)
′
4.6m
W
=
R
SENSE
V
I
Load, max
+
1.0A
----------------------------------------
1
TF
–
(
)
′
=
=
1.0A
14.5A
+
------100mV
1
5%
–
(
)
′
6.1m
W
=
Table 8. R
sense
for various load currents
RC5040 Short Circuit Current Characteristics
The RC5040 has a short circuit current characteristic that
includes a hysteresis function that prevents the DC-DC con-
verter from oscillating in the event of a short circuit. A typi-
cal V-I characteristic of the DC-DC converter output with a
sense resistor of 6 m
W
is presented in the Typical Operating
Characteristics section, page 5. The converter performs with
a normal load regulation characteristic until the voltage
across the resistor reaches the internal short circuit threshold
of 120mV. At this point, the internal comparator trips and
sends a signal to the controller to turn off the gate drive to the
power MOSFET. This causes a drastic reduction in the out-
put voltage as the load regulation collapses into the short cir-
cuit mode of control. The output voltage will not return to
the normal load characteristic until the output short circuit
current is reduced to within the safe range for the DC-DC
converter.
I
Load,max
(A)
10.00
11.20
12.40
13.90
14.00
14.50
R
SENSE
PC Trace
Resistor (m
W
)
6.5
5.8
5.3
4.8
4.7
4.6
R
SENSE
Discrete
Resistor (m
W
)
8.6
7.8
7.1
6.4
6.3
6.1