MC33394DWB Freescale Semiconductor, MC33394DWB Datasheet - Page 29

• 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

The peak–to peak ripple current value is: I L = 0.345 A.
The peak inductor current is given by:
I Lpk = 0.5 I L + I o = 0.5x0.345 + 1.2 = 1.37[A]
of the 33394 internal switch current limit I lim(max) = 3.0 A.
requirements are met, for example by the PO250.473T
inductor from Pulse Engineering, Inc.
5.2.1.2. Selecting the Catch Diode D 1
calculated average current value.
rectifier D 1 is given by maximum input voltage (maximum
transient battery voltage). These requirements are met, for
example by the HSM350 (3 A, 50 V) schottky diode from
Microsemi, Inc.
5.2.1.3. Selecting the Output Capacitor
therefore the 100 F tantalum capacitor with 80 m ESR was
chosen.
From the formula for calculating the ripple voltage:
the internal switch Q1 and inductor series resistance can be
estimated as:
Where:
resistances, R DSon of the internal power switch and inductor
series resistance R L.
For the worst case conditions:
R D = R DSon(max) + R L = 0.25 + 0.1 = 0.35[ ]
I pk(min) is the minimum internal power switch current limit
value.
follows:
D
+
+
H, which gives 47 H standard component value.
MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA
I L
After substitution, the calculated inductance value is L = 45
The inductor saturation current is given by the upper value
Considering also the inductor serial resistance, these
The rectifier D 1 current capability has to be greater than
The maximum reverse voltage stress placed upon this
The output capacitor C o should be a low ESR part,
The input voltage drop associated with the resistance of
V D is the voltage dissipated on the major parasitic
Then the equation for calculating I L can be modified as
3.5
125[mA]
47
V D
+
V in
*
V in
[
0.875
10
I pk(min)
*
L
*
6
V RES
V D
R D
[(6
[ (V o
)
R D
0.5)
I L
)
(6
L
+
)
V fwd2 )
(V o
*
2.5 A
0.5)
Q 2
(3.5
)
Freescale Semiconductor, Inc.
*
V fwd2 )
*
Figure 16. 33394 Switcher Topology – Boost Mode
For More Information On This Product,
0.2
(V in
0.35
I Q
0.875)]
V fwd2
D 2
*
W
10
V D ) ]
f
ESR
+
6
Go to: www.freescale.com
0.875 V
0.75
+
C O
d
+
+
–
V O
33394
R LOAD
V ppESR = I L x R ESR = 0.345 x 0.08 = 28 [mV]
temperature stability requirements is, for example, the
TPSV107K020R0085 tantalum capacitor from AVX Corp.
Boost Converter Power Capability
able to deliver the required power.
technique, the Boost converter output ripple voltage is higher
than if it utilized a typical PWM control method. Therefore the
switcher output voltage level is set higher than in the Buck
mode (in the Boost mode VPRE = +6 V), in order to maintain
a sufficient dropout voltage for the 5–volt linear regulators
(VDDH, VREFs) and to avoid unwanted Resets to the
microcontroller.
converter occur with the lowest input voltage:
V in(min) = 3.5 V
I o = 0.8 A
Vpre = +6 V
f = 200 kHz
V fwd1 = V fwd2 = 0.5 V
d = 0.75, duty cycle is fixed at 75% in boost mode
calculated as:
higher than the required output power or:
Where P in(max) is the boost converter maximum input power:
estimated to be h = 85%, and includes switching losses of the
external power switch Q2 (MOSFET) inductor and capacitors
AC losses, and output rectifier D2 (schottky) switching
losses.
power loss of the output rectifier D2:
P out
P in
+
meets the required criteria.
One device that meets both, the low ESR, and the
The boost converter with selected components has to be
Due to the nature of this non–compensated PFM control
The most stringent conditions for the 33394 boost
Then the maximum average input current can be
Finally, the boost converter power capability has to be
h is the boost converter efficiency, in our case h is
P out is the boost converter output power, which includes
As can be seen, the boost converter input power capability
(3.5
+
I inAve
P in(max)
+
(V in
*
(V o
0.875)
+
*
)
I pk(min)
V D )
V fwd2 )
I LIM
I 01
I 02
h
I L
u
2.43
P out
I inAve
*
I o
1
2
D
0.85
+
L1 > L2
D
I O1 > I O2
I L
I L1 <
(6
h
+
+
+
)
D
2.5
I L2
5.42[W]
0.5)
*
0.125
2
0.8
T
I L1
I L2
+
+
2.43[A]
5.2[W]
t
29