MC33463H Просмотр технического описания (PDF) - Motorola => Freescale
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MC33463H Datasheet PDF : 12 Pages
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MC33463
Figure 13. Output Voltage versus Temperature
5.1
1.0
Figure 14. Startup/Hold Voltage
versus Temperature
5.0
4.9
4.8
–40
MC33463H–50KT1
L = 120 µH
–20
0
20
40
60
80
TA, AMBIENT TEMPERATURE (°C)
0.8
0.6
0.4
0.2
–40
Vstart
Vhold
–20
0
MC33463H–50KT1
L = 120 µH
IO = 1.0 mA
20
40
60
80
TA, AMBIENT TEMPERATURE (°C)
DEFINITIONS
Quiescent Bias Current – Current which is used to operate
the switching regulator chip and is not delivered to the load.
Leakage Current – Current drawn through a transistor
junction, under a specified collector voltage, when the
transistor is off.
FUNCTIONAL DESCRIPTION
Introduction
The MC33463 series are monolithic power switching
regulators optimized for dc–to–dc converter applications
where power drain must be minimized. The combination of
features in this series allows the system designer to directly
implement step–up, step–down or flyback converters with a
small number of external components. Potential applications
include low power consumer products and battery powered
portable products. Typical application circuits are shown in
Figure 15 and Figure 16.
Operating Description
The MC33463 series converters each operate as a fixed
on–time, variable off–time voltage mode ripple regulator.
Operation is intended to be in the discontinuous mode, where
the inductor current ramps up to a peak value which is greater
than or equal to twice the value of the dc input current during
the on–time of the transistor switch. During the off–time of the
transistor switch, the inductor current ramps down to zero and
remains at zero until another switching cycle begins.
Because the output voltage pin is also used as the supply
voltage for powering internal circuitry, an external startup
circuit is needed in step–down and flyback converter designs
to provide initial power to the integrated circuit to begin
switching. The startup circuit needed can be three discrete
components, as shown in Figure 17, or a micropower
undervoltage sensor, as shown in Figure 18.
Oscillator
The oscillator frequency, is internally programmed to
100 kHz. The duty ratio of the oscillator is designed for a
constant value of 0.75 nominal. Hence the nominal on–time
of the power switch is:
+ + + ton
D
fosc
0.75
(100 kHz)
7.5 µs
Feedback Comparator
The output voltage is sensed and fed to a high speed
comparator noninverting input through an internal resistive
divider. The comparator inverting input is connected to an
internally trimmed to 0.7 V reference.
With a voltage mode ripple converter operating under
normal conditions, output switch conduction is initiated and
terminated by the oscillator, off–time is controlled by the high
speed voltage feedback comparator.
Driver and Output Switch
To aid in system design flexibility and conversion
efficiency, two output driver options are provided. The
MC33463H–XXKT1 converters have an internal drive
transistor which is capable of sinking currents greater than
60 mA into the Lx pin. An internal VLx limiter circuit senses if
the Lx pin voltage exceeds 1.0 V during ton and turns off the
drive transistor. The MC33463H–XXLT1 provides output
drive for an external transistor.
Applications
The following converter applications show the simplicity
and flexibility of the converter architecture. Three main
converter topologies are demonstrated in Figures 15 through
19.
6
MOTOROLA ANALOG IC DEVICE DATA
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