MC33394DH Freescale Semiconductor, MC33394DH Datasheet - Page 25

• 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

that are required by the 33394. The IC is designed to operate
in an automotive environment. Conducted immunity and
radiated emissions requirements have been addressed
during the design. However, the IC requires some external
protection.
battery. The module designer should use an MOV or another
transient voltage suppressor in all cases, when the load
dump transition exceeds + 45 volts with respect to ground.
Protection should also include a reverse battery protection
diode (or relay) and input filter. This is required to protect the
33394 from ESD and +/– 300V ignition transients. Typical
configurations are shown in Figure 1. Outputs and inputs
connected directly to connector pins require module level
ESD protection.
5.1. Selecting Components for Linear Regulators
different purposes. It maintains the linear regulator loop
stability, and it provides an energy reservoir to supply current
during very fast load transients. This is especially true when
supplying highly modulated loads like microcontrollers and
other high–speed digital circuits. Due to the limited
bandwidth of the linear regulators, the output capacitor is
selected to limit the ripple voltage caused by these abrupt
changes in the load current. During the fast load current
transients, the linear regulator output capacitor alone
controls the initial output voltage deviation. Hence, the output
capacitor’s equivalent series resistance (ESR) is the most
critical parameter.
conditions (the VREF e.g.), use the output capacitor mainly
for stability purpose, and therefore its capacitance value can
be significantly smaller. The typical output capacitor
parameters are: C = 1.0
ceramic 1 F capacitor is used, the ESR can be provided by
a discrete serial resistor (see Figure 20).
capacitance for a heavily loaded output supplying digital
circuits.
5.1.1. Selecting the Output Capacitor Example:
sufficiently low ESR. The selected capacitor must have an
adequate voltage, temperature and ripple current rating for
the particular application.
parameters, several assumptions will be made.
1) During the very fast load current transients, the linear
regulator can not supply the required current fast enough,
and therefore for a certain time the entire load current is
supplied by the output capacitor. 2) The capacitor’s
equivalent series inductance (ESL) is neglected. These
assumptions can greatly simplify the calculations, and are
MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA
This section provides information on external components
Protection is required for all pins connected directly to
The output capacitor of the linear regulator serves two
The outputs, which do not experience such severe
The following example shows how to determine the output
The output capacitance must be selected to provide
In order to calculate the proper output capacitor
F; ESR = 2.0 ohms. When a
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33394
reasonable for most of practical applications. Then the ESR
of the output capacitor has to satisfy the following condition:
Where:
caused by the load current transient.
the abrupt step in the linear regulator load current.
is considered with the maximum voltage drop of 100mV. This
gives the output capacitor’s maximum ESR value of:
order to maintain the linear regulator stability and to satisfy
large load current steps requirements the solid tantalum
capacitor 100 F/10V with ESR = 200 m . One device that
meets these requirements is the TPSC107K010S020
tantalum capacitor from the AVX Corporation.
capacitance can be calculated:
Where:
C is the output capacitance.
D
the abrupt step in the linear regulator load current.
voltage drop in the voltage regulator output caused by the
current fast transient can be calculated as:
be placed in parallel to provide filtering for the high frequency
transients caused by the switching regulator.
microprocessor supply pin should be used as well. Table 1
shows the suggested output capacitors for the 33394 IC
linear regulator outputs.
include key off timing for memory retention. Though the
VKAM is not a heavily loaded output, the VKAM output
capacitor has to have a sufficiently large capacitance value to
supply current to the microcontroller for a certain time after
battery voltage is disconnected.
D
Vo is the maximum allowed linear regulator voltage drop
Io is the maximum current transient, which can occur due to
I o is the maximum current transient, which can occur due to
t is the linear regulator response time.
In this example the VDDH output with the 400 mA load step
This level of ESR requires a relatively large capacitance. In
In the next step, the voltage drop associated with the
Assuming that the capacitor ESL is negligible, the total
A ceramic capacitor with capacitance value 10nF should
Properly sized decoupling ceramic capacitor close to the
Other factors to consider when selecting output capacitors
V total
D
V ESR
+
D
V C
+
D
V ESR
ESR
+
ESR
D
I o
)
+
C
ESR
D
D
100 mV
400 mA
I o
D
V C
t
+
v
+
+
200 m
D
0.4 A
D
80 mV
V o
I o
+
100
250 m
W
m
)
5
F
400 mA
m
20 mV
W
s
+
20 mV
+
+
100 mV
80 mV
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