Datasheet

1
2
f
p
=
× × ×
zmod
RESR Cout
f f f= ×co pmod zmod
2
f
f f= ×
sw
co pmod
2
ea ps
c Vout Cout
R2
gm Vref gm
× × ×
=
× ×
fp
Vout Cout
C3
Iout R2
×
=
×
1
2
f
p
=
× × ×
p
R2 Cp
Vout=50mV/div(accoupled)
Iout=2A /div(1.5 A to4.5loadstep)
Time=500 μsec/div
Vin=10V/div
EN=2V/div
SS/TR=1V/div
Vout=2V/div
Time=2msec/div
Vin=10V/div
EN=2V/div
SS/TR=1V/div
Vout=2V/div
Time=2msec/div
Vin=5V/div
Vout=2V/div
Voutstartingfrompre-biasvoltage
Time=20msec/div
TPS54620
www.ti.com SLVS949C –MAY 2009– REVISED MAY 2011
(32)
(33)
(34)
Now the compensation components can be calculated. First calculate the value for R2 which sets the gain of the
compensated network at the crossover frequency. Use Equation 35 to determine the value of R2.
(35)
Next calculate the value of C3. Together with R2, C3 places a compensation zero at the modulator pole
frequency. Equation 36 to determine the value of C3.
(36)
Using Equation 35 and Equation 36 the standard values for R2 and C3 are 1.69 kΩ and 8200 pF.
An additional high frequency pole can be used if necessary by adding a capacitor in parallel with the series
combination of R2 and C3. The pole frequency is given by Equation 37. This pole is not used in this design.
(37)
Application Curves
LOAD TRANSIENT STARTUP with VIN
Figure 35. Figure 36.
STARTUP with EN STARTUP with PRE-BIAS
Figure 37. Figure 38.
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