MC33470DW ON Semiconductor, MC33470DW Datasheet - Page 8

• Manufacturer Part Number: MC33470DW
• Description: IC CONV DC/DC SYNC RECT 20-SOIC
• Manufacturer: ON Semiconductor

Specifications of MC33470DW

• Applications: Controller, Intel Pentium® II
• Voltage - Input: 4.5 ~ 5.5 V
• Number Of Outputs: 1
• Voltage - Output: 1.8 ~ 3.5 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 20-SOIC (7.5mm Width)
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

switching regulator specifically designed for dc−to−dc
converter applications which provide a precise supply voltage
for state of the art processors. The MC33470 operates as fixed
frequency, voltage mode regulator containing all the active
functions
programmable step−down synchronous rectification with a
minimum number of external components.
Oscillator
300 kHz. The charge to discharge ratio is controlled to yield
a 95% maximum duty cycle at the switch outputs. During the
fall time of the internal sawtooth waveform, the oscillator
generates an internal blanking pulse that disables the G1 output
switching MOSFET. The internal sawtooth waveform has a
nominal peak voltage of 2.5 V and a valley voltage of 1.5 V.
Pulse Width Modulator
the oscillator ramp voltage applied to the noninverting input,
while the error amplifier output is applied to the inverting
input. Output switch conduction is initiated when the ramp
waveform is discharged to the valley voltage. As the ramp
voltage increases to a voltage that exceeds the error
amplifier output, the latch resets, terminating output G1
MOSFET conduction, and turning on output G2 MOSFET,
for the duration of the oscillator ramp. This PWM/latch
The MC33470 is a monolithic, fixed frequency power
The oscillator frequency is internally programmed to
The pulse width modulator consists of a comparator with
Compensation
Internal
required
5.0 V
2.5 V
1.5 V
12 V
V
G1
G2
ref
to
directly
implement
OPERATING DESCRIPTION
Figure 15. Timing Diagram
digitally
http://onsemi.com
UVL Threshold
MC33470
UVL Threshold
8
combination prevents multiple output pulses during a given
oscillator cycle.
noninverting inputs of a pair of high speed comparators. The
high speed comparators’ inverting inputs are tied 0.96 x V
and 1.04 x V
to load changes. When load transients which cause the output
voltage to fall outside a "4% regulation window occur, the
high speed comparators override the PWM comparator to
force a zero or maximum duty cycle operating condition until
the output voltage is once again within the linear window.
V
of the supply voltage levels. Both G1 and G2 output pins are
held low until the V
Error Amplifier and Voltage Reference
having a nominal transconductance of 800 mmho. The
transconductance has a negative temperature coefficient.
Typical transconductance is 868 mmho at 0°C and 620 mmho
at 125°C junction temperature. The amplifier has a cascode
output stage which provides a typical 3.0 Mega−Ohms of
impedance. The typical error amplifier dc voltage gain is
67 dB.
P V
CC
The sense voltage input at Pin 6 is applied to the
When voltages are initially provided to the supply pins,
The error amplifier is a transconductance type amplifier,
CC
and
pin voltage exceeds 9.0 V.
P V
ref
CC
, respectively, to provide an optimum response
, undervoltage lockout circuits monitor each
CC
pin voltage exceeds 4.0 V and the
Timing Capacitor
ref