Datasheet
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Setting Overcurrent Protection
V
ILIM
+ 2.7 I
PH(max)
R
CS
(7)
I
PH(max)
+
I
OUT
2
)
ǒ
V
IN
* V
OUT
Ǔ
V
OUT
2 L
OUT
f
SW
V
IN
(8)
Resistor Divider Calculation for VOUT, ILIM, OVSET and UVLO
R
BIAS
+ 0.7
R1
ǒ
V
OUT
* 0.7
Ǔ
(9)
R6 + R5
V
ILIM
ǒ
0.7 * V
ILIM
Ǔ
(10)
R4 + 0.812
R3
ǒ
V
OUT(ov)
* 0.812
Ǔ
(11)
R8 + 1.0
R7
ǒ
V
IN
* 1.0
Ǔ
(12)
Feedback Loop Compensation
f
OP
+
1
2p R
OUT
C
OUT
(13)
f
ESRZ
+
1
2p R
ESR
C
OUT
(14)
TPS40130
SLUS602B – JUNE 2004 – REVISED SEPTEMBER 2005
Setting the overcurrent protection is given in the following equations. Care must be taken when calculating V
ILIM
to include the increase in R
CS
caused by the output current as it approaches the overcurrent trip point. The DCR
(R
CS
in the equation) of the inductor increases approximately 0.39% per degree Centigrade.
where
• I
PH(max)
is a maximum value of the phase current allowed
• I
OUT
is the total maximum DC output current
• L
OUT
is the output inductor value
• f
SW
is the switching frequency
• V
OUT
is the output voltage
• V
IN
is the input voltage
• R
CS
is a value of the current sense resistor used or the DCR value of the output inductor, L
OUT
Use Figure 9 for setting the output voltage, current limit voltage and overvoltage setting voltage. Select R
BIAS
using Equation 9 . With a voltage divider from V
REF
, select R6 using Equation 10 . WIth a voltage from DIFFO
select R4 using Equation 11 . With a voltage divider from V
IN
, select R8 using Equation 12 .
The TPS40130 operates in a peak-current mode and the converter exhibits a single pole response with ESR
zero for which Type II compensation network is usually adequate as shown in Figure 5 .
The load pole is situated at a value calculated using Equation 13 .
and the ESR zero is situated at a value calculated using Equation 14 .
To achieve the desired bandwidth the error amplifier has to compensate for modulator gain loss at the crossover
frequency. A zero placed at the load pole frequency facilitates that. The ESR zero alters the modulator -1 slope
at higher frequencies. To compensate for the ESR zero, a pole in the error amplifier transfer function should be
placed at the ESR zero frequency.
15
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