MC33394DWB Freescale Semiconductor, MC33394DWB Datasheet - Page 28

• Manufacturer Part Number: MC33394DWB
• Description: IC POWER SUPPLY MULT-OUT 54-SOIC
• Manufacturer: Freescale Semiconductor

Specifications of MC33394DWB

• Applications: Motorola MPC55x, MPC56x Microprocessors
• Interface: SPI Serial
• Voltage - Supply: 4 V ~ 26.5 V
• Package / Case: 54-SOIC (0.300", 7.50mm Width) Exposed Pad
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Where I o is the average output current.
equation:
5.2.1. Switching Regulator Component Selection
values (see Figure 15) is a compromise between the two
modes of operation of the switching regulator, the pre
regulated voltage VPRE and the dropout voltage of the linear
regulators. Ideal equations describing the peak—peak
inductor current ripple, peak—peak output voltage ripple and
peak inductor current are shown below. Since the switching
regulator will work mostly in the buck mode, the inductor and
the switcher input and output capacitor were selected for
optimum buck controller performance, but also taking into
account the restriction placed by adopting the boost
converter as well.
the component values. The VPRE output is set to regulate to
28
The inductor peak current is given by the following
The selection of the external inductor L2 and capacitor C2
The following example shows a procedure for determining
V in
I Q
Q 1
Figure 15. 33394 Switcher Topology
V RDS(on)
R DS(on)
D 1
V IN
V in
V in
POWER SWITCH OFF
POWER SWITCH ON
V fwd1
V RL
R L
I L
L
I ON
Figure 14. Basic Boost Converter Operation and its Waveforms
I OFF
Q
I L
I L
L
Freescale Semiconductor, Inc.
Q 2
L
I Q
For More Information On This Product,
I D
D
V fwd2
V out
V out
D 2
ESR
+
C O
C O
+
C O
+
C O
+
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I LOAD
I LOAD
+
–
+
+
+
–
–
–
V O
V O
R LOAD
R LOAD
R LOAD
R LOAD
33394
MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA
5.6 V and the linear regulators require a minimum of 0.4 V
dropout voltage. This leaves a
peak—to–peak output voltage ripple. Assuming the following
conditions:
V in (typ) = 13.5 V
I o = 1.2
VPRE = 5.6 V (+6 V in the boost mode)
f = 200 kHz
V fwd1 = V fwd2 = 0.5 V
V pp(max) = 0.2 V/2 = 0.1 V (to allow for process and
temperature variations).
5.2.1.1. Selecting the Inductor
ripple current I L has to be determined. The usual ratio of I L
to output current I o is:
account the 33394 switcher topology (see Figure 15), the
inductor ripple current can be estimated as:
I L = 0.3 I o
Maximum allowed output voltage ripple in the buck mode
In order to select the proper inductance value, the inductor
As described in the previous
V Co
V Q
I D
I Q
I L
D
I L
t on
+
T
(V in
t off
Ipk L
*
+
V o
L
I o
*
V fwd2 )
V in
V o
D
I L
)
section,
0.2 V window for the
1
2
D
V o
I L
V in
)
and taking into
V fwd2
t
f
I O