CS5166GDWR16 View Datasheet(PDF) - ON Semiconductor
Part Name
Description
MFG CO.
'CS5166GDWR16' PDF : 25 Pages View PDF
CS5166
This series resistor affects the calculation of the current
limit setpoint, and has to be taken into account when
determining an effective current limit.
The calculations below show how the current limit
setpoint is determined when this 510 Ω is taken into
consideration.
VTRIP + VTH ) (ISENSE RISENSE) * (RFB IFB)
Where:
VTRIP = voltage across the droop resistor that trips the
ISENSE comparator.
VTH = internal ISENSE comparator threshold
ISENSE = ISENSE bias current
RISENSE = ISENSE pin 510 Ω filter resistor
RFB = VFB pin 3.3 k filter resistor
IFB = VFB bias current
Minimum current sense resistor (droop resistor) voltage
drop required for current limit when RISENSE is used
VTRIP(MIN) + 55 mV ) (13 mA 510) * (3.3 k 1.0 mA)
+ 55 mV ) 6.6 mV * 3.3 mV + 58.3 mV
Nominal current sense resistor (droop resistor) voltage
drop required for current limit when RISENSE is used
VTRIP(NOM) + 76 mV ) (30 mA 510) * (3.3 k 0.1 mA)
+ 76 mV ) 15.3 mV * 0.33 mV + 90.97 mV
Maximum current sense resistor (droop resistor) voltage
drop required for current limit when RISENSE is used
VTRIP(NOM) + 110 mV ) (50 mA 510)
+ 110 mV ) 25.5 mV + 135.5 mV
The value of RSENSE (current sense PCB trace) is then
calculated:
RSENSE(MAX)
+
58.3 mV
14.2 A
+
4.1
mW
RSENSE(NOM)
+
RSENSE(MAX)
1.29
+
4.1 mWm
1.29
+
3.18
mW
The range of load currents that will cause the internal
current sense comparator to detect an overload condition is
as follows:
Nominal Current Limit Setpoint
ICL(NOM)
+
VTRIP(NOM)
RSENSE(NOM)
Therefore,
ICL(NOM)
+
90.97 mV
3.18 mW
+
28.6
A
Maximum Current Limit Setpoint
ICL(MAX)
+
VTRIP(MAX)
RSENSE(MAX)
Therefore,
ICL(MAX)
+
135 mV
3.18 mW 0.71
+
60
A
Therefore, the range of load currents that will cause the
internal current sense comparator to detect an overload
condition through a 3.0 mΩ embedded PCB trace is: 14.2 A
< ICL 60 A, with 28.6 A being the nominal overload
condition.
Design Rules for Using a Droop Resistor
The basic equation for laying an embedded resistor is:
RAR + ò
L
A
or R +
ò
L
(W t)
where:
A = W × t = cross−sectional area
ρ = the copper resistivity (μΩ − mil)
L = length (mils)
W = width (mils)
t = thickness (mils)
For most PCBs the copper thickness, t, is 35 μm (1.37
mils) for one ounce copper. ρ = 717.86 μΩ−mil
For a Pentium II load of 14.2 A the resistance needed to
create a 43 mV drop at full load is:
Response
Droop
+
43 mV
IOUT
+
43 mV
14.2 A
+
3.0
mW
The resistivity of the copper will drift with the
temperature according to the following guidelines:
DR + 12% @ TA + ) 50°C
DR + 34% @ TA + ) 100°C
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