MC33394DWB Freescale Semiconductor, MC33394DWB Datasheet - Page 26

• 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

5.2. Switching Regulator Operation
switching converter topologies. One is the typical voltage
mode PWM step–down or buck regulator, which provides
pre–regulated VPRE voltage (+5.6 V) during normal
operating conditions.
input voltage for the 33394 can fall below the lower operating
limit of the step–down converter. Under such conditions, the
step–up or boost converter provides the required value of the
VPRE voltage. The following paragraphs describe the basic
principles of the two converters operation.
Buck Mode
has two distinct parts: the power switch on state and the off
state. When the power switch is on, one inductor terminal is
connected to the input voltage Vin, and the other inductor
terminal is the output voltage V o . During this part of the
switching period the rectifier (catch diode) is back biased,
and the current ramps up through the inductor to the output:
Where:
t on is the on–time of the power switch.
V in is the input voltage.
V o is the output voltage.
i L(on) is the inductor current during the on–time.
L is the inductance of the inductor L.
stores energy in the inductor core.
source Vin is disconnected from the circuit. The energy
stored in the core forces current to continue to flow in the
same direction, the rectifier is forward biased and the
Table 1. Linear Regulator Output Capacitor Examples
VDDH
VPP
VDD3_3
VDDL
VREFx
VKAM*
26
The 33394 switching regulator circuit consists of two basic
During cold start–up, when the car battery is weak, the
One switching cycle of the step–down converter operation
During the on time, current ramping through the inductor
During the off time of the power switch, the input voltage
Output
i L(on)
+
(V in
100uF/10V
33uF/10V
68uF/6.3V
100uF/6.3V
10uF/16V
100uF/6.3V
*
V o )
L
Freescale Semiconductor, Inc.
For More Information On This Product,
Value/Rating
t on
Go to: www.freescale.com
33394
MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA
TPSC107K010S0200
TPSB336K010S0650
TPSC686K006S0200
TPSC107K006S0150
THJB106K016S
TPSC107K006S0150
inductor input voltage is clamped one forward diode drop
below ground. The inductor current during the off time is:
Where:
t off is the off–time of the power switch.
i L(off) is the inductor current during the off time.
V fwrd is forward voltage drop across the rectifier.
During the steady state operation i L(on) = i L(off) = I L , and
V in /V o = d
Where:
d is the duty cycle, and d = t on /T.
T is switching period, T = 1/f.
f is the frequency of operation.
C o . The first describes ripple voltage caused by current
variation upon the output capacitance C o :
capacitor equivalent series resistance ESR:
converter ripple voltage:
V ppESR >>V ppCo
Where:
I o is the average output current.
Two relations give the ripple voltage in the output capacitor
The other is caused by current variations over the output
Practically, the ESR contributes predominantly to the buck
The inductor peak current can be calculated as follows:
SMD tantalum
i L(off)
Vpp ESR
Part n. (AVX Corp.)
Vpp Co
+
Ipk L
(V o
+
+
+
*
I o
D
8Co
V fwd )
I L
)
D
L
I L
1
2
D
R ESR
I L
f
t off