SC2545TSTRT View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
SC2545TSTRT Datasheet PDF : 24 Pages
| |||
SC2545
POWER MANAGEMENT
Applications Information (Cont.)
The compensator in Figure 10 includes an error ampli-
fier and impedance networks Zf and Zs. It is implemented
by the circuit in Figure 12. The compensator provides an
integrator, double poles, and double zeros. As shown in
Figure 11, the integrator is used to boost the gain at low
frequency. Two zeros are introduced to compensate ex-
cessive phase lag at the loop gain crossover due to
the integrator (-90deg) and the complex pole pair (-
180deg). Two high frequency poles are designed to com-
pensate the ESR zero and to attenuate high frequency
noise.
)S 8PHQ@IT6UPSÃB6DI )S
B6DIÃq7
)]
)]
)R
GPPQÃB6DI
)]
8PIW@SU@SÃB6DI )F
AS@RV@I8`ÃC
Fig. 11. Bode plots for control loop design.
A resistive divider is used to program the output voltage.
The top resistor Rtop of the divider in Fig. 12 can be cho-
sen from 20k : to 30k : . Then the bottom resistor
Rbot is found from:
5ERW 9 5WRS
9R 9
where 0.75V is the internal reference voltage of the
SC2545.
The other components of the compensator can be cal-
culated using following design procedure:
(1). Plot the converter gain, including LC filter and PWM
modulator.
(2). Select the open loop crossover frequency Fc located
at 10% to 20% of the switching frequency. At Fc, find the
required DC gain.
(3). Use the first compensator pole Fp1 to cancel the
ESR zero Fz.
(4). Have the second compensator pole Fp2 at half the
switching frequency to attenuate the switching ripple and
high frequency noise.
(5). Place the first compensator zero Fz1 at or below
50% of the power stage resonant frequency Fo.
(6). Place the second compensator zero Fz2 at or below
the power stage resonant frequency Fo.
A MathCAD program is available upon request for the
&
calculation of the compensation parameters.
&
5
&
5
9F
2XW
5WRS
9R
($
5ERW
9
Fig. 12. Compensation network.
ã 2005 Semtech Corp.
16
www.semtech.com
Share Link: 