MC33394DH Freescale Semiconductor, MC33394DH Datasheet - Page 31

• Manufacturer Part Number: MC33394DH
• Description: IC POWER SUPPLY MULT-OUT 44-HSOP
• Manufacturer: Freescale Semiconductor

Specifications of MC33394DH

• Applications: Motorola MPC55x, MPC56x Microprocessors
• Interface: SPI Serial
• Voltage - Supply: 4 V ~ 26.5 V
• Package / Case: 44-BSOP (0.433", 11.00mm Width) Exposed Pad
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

components starts with analysis of the open loop (modulator)
transfer function, which has to be determined and plotted into
the Bode plot (see Figure 19). The modulator DC gain can be
determined as follows:
voltage to change the duty cycle from 0 to 100 percent (V e =
2.6 V at Vbat =14 V).
modulator transfer function has a double complex pole
caused by the output L–C filter. Its corner frequency can be
calculated as:
a —180 degree phase shift.
function is the zero caused by the ESR of the output
capacitor C o and the capacitance of the output capacitor
itself:
and +90 degree phase shift.
appropriate compensation can be applied in order to obtain
the required closed loop cross over frequency and phase
margin (~60 degree) — refer to Figure 18 and Figure 19.
gain–phase plot, E/A gain–phase plot, closed loop
gain–phase plot, and the E/A compensation circuit. The
frequency f xo is the required cross–over frequency of the
buck regulator.
bandwidth) and stability of the voltage–mode controlled buck
PWM regulator the two–pole–two–zero type of compensation
was selected — see Figure 19 for the compensated Error
Amplifier Bode plot, and Figure 18 for the compensation
network. The two compensating zeros and their positive
phase shift (2 x +90 degree) associated with this type of
compensation can counteract the negative phase shift
caused by the double pole of the modulator’s output filter.
MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA
The process of determining the right compensation
Where V e is the maximum change of the Error Amplifier
As can be seen from Figure 19, the buck converter
This double pole exhibits a —40dB per decade rolloff and
Another point of interest in the modulator’s transfer
The ESR zero causes +20dB per decade gain increase,
Once the open loop transfer function is determined, the
Figure 19 shows the 33394 Switching Regulator modulator
In order to achieve the best performance (the highest
Figure 18. Error Amplifier Two–Pole–Two–Zero
VPRE_S
Compensation Network
f z(ESR)
R3
R1
f p(LC)
A DC
R
C3
+
+
+
2
2
D
p
V in
p
R ESR C o
V e
R2
Ref
Freescale Semiconductor, Inc.
1
–
+
LC o
1
C1
For More Information On This Product,
E/A
C2
U1
VCOMP
Go to: www.freescale.com
33394
be calculated from the following expressions:
and the required absolute gain is:
Table 2 for the 33394 switcher component values.
–180
–270
–360
The frequency of the compensating poles and zeros can
Refer to Application Schematic Diagram (Figure 20) and
–20
–40
–60
–90
80
60
40
20
90
0
0
1
1
Figure 19. Bode Plot of the Buck Regulator
AMPLIFIER
ERROR
f z2
MODULATOR
10
10
f p2
ERROR AMPLIFIER
CLOSED LOOP (overall)
+
MODULATOR
A 2
+
2
+
p
2
(R 1
100
100
f z1
f p1
C 1
p
R 2 (R 1
R 2 C 1 C 2
A 1
)
+
+
)
1
R 1 R 3
CLOSED LOOP (overall)
f p(LC)
f Z1
R 3 )C 3
+
2
C 2
2
f (Hz)
1000
f (Hz)
)
1000
p
p
R 2 C 2
R 3 C 3
R 2
R 1
A 1
1
1
R 3 )
[
f Z(ESR)
[
2
f Z2
[
p
2
R 2 C 1
f p1
10 k
10 k
If xo
p
1
R 2
R 3
R 1 C 3
1
A 2
f p2
100 k
100 k
31
1 M
1 M