RC5041
PRODUCT SPECIFICATION
1
Table 5. Comparison of Sense Resistors
Discrete Metal
Discrete
Discrete Iron
Alloy
resistor (IRC) (Dale)
Strip surface
mount resistor Alloy wire
Discrete MnCu
CuNi Alloy
wire resistor
(Copel)
Motherboard
Trace Resistor
Description
resistor
Tolerance
±29%
±5%
±1%
±10%
±10%
Factor (TF)
(±1% available)
Size
(L x W x H)
2" x 0.2" x 0.001" 0.45"x0.065"x 0.25" x 0.125" x 0.200" x 0.04" x
0.200" x 0.04" x
0.100"
(1 oz Cu trace)
0.200"
0.025"
0.160"
Power capability >50A/in
1 watt
1 watt
1 watt
1 watt
(3W and 5W
available)
Temperature
Coefficient
+4,000 ppm
Low
+30 ppm
±75 ppm
±30 ppm
±20 ppm
Cost
$0.31
$0.47
$0.09
$0.09
@10,000 piece included in
motherboard
Notes:
1.Refer to Appendix A for Directory of component suppliers.
(Ipk – Imin
)
(5.0 – 14.5 × 0.037 – 3.3)
-------------------------------------------------------------
--------------------------- =
×
• For discrete resistor and I
= 14.5A:
load, max
1.3 × 10–6
2
Vth,min
----------------------------------------------------
1.0A + ILoad, max + IR
RSENSE
=
× (1 – TF)
(3.3 + 0.5)
1
-------------------------------------------------------------- -----------------------
×
= 1.048A
650 × 103
(5.0 – 14.5 × 0.037 + 0.5)
100mV
2.0A + 14.5A
---------------------------------
=
× (1 – 5%) = 5.75mΩ
Therefore, the peak current, I , through the inductor for a
PK
14.5A load is found to be:
For user convenience, Table 6 lists recommended value for
sense resistor for various load current using embedded PC
trace resistor or discrete resistor.
(IPK – Imin
)
I
SC ≥ Iinductor = ILoad, max + ----------------------------- = 14.5 + 1 = 15.5A
2
As a result, the short circuit detection threshold must be at
least 15.5A
Table 6. R
for Various Load Current
sense
R
R
SENSE
SENSE
I
PC Trace
Resistor (mΩ)
Discrete
Resistor (mΩ)
Load,max
The next step is to determine the value of the sense resistor.
Including sense resistor tolerance, the sense resistor value
can be approximated as follows:
(A)
10.00
11.20
12.40
13.90
14.00
14.50
5.9
5.4
4.9
4.5
4.4
4.3
7.9
7.2
6.6
6.0
5.9
5.7
Vth,min
Vth,min
-----------------
1 + ISC
----------------------------------------------
1.0 + ILoad,max + IR
RSENSE
=
× (1 – TF) =
× (1 – TF)
Where TF = Tolerance Factor for the sense resistor.
= Ripple Current = 1A
I
R
There are several different type of sense resistors. Table 7
describes tolerance, size, power capability, temperature
coefficient and cost of various type of sense resistors:
Based on the Tolerance in Table 5,
• For Embedded PC Trace Resistor and for
Il
oad,max
= 14.5A:
Vth,min
----------------------------------------
2.0A + ILoad, max
RSENSE
=
× (1 – TF)
100mV
2.0A + 14.5A
---------------------------------
=
× (1 – 29%) = 4.3mΩ
12
RAYTHEON [ RAYTHEON COMPANY ]
