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부품번호 PL494 기능
기능 PULSE-WIDTH-MODULATION CONTROL CIRCUITS
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PL494 데이터시트, 핀배열, 회로
PL494
Revised Date : 2007/11/20
Page No. : 1/14
PULSE-WIDTH-MODULATION
CONTROL CIRCUITS
˙Complete PWM Power Control Circuitry
˙Uncommitted Outputs for 200-mA Sink or
Source Current
˙Output Control Selects Single-Ended or
Push-Pull Operation
˙Internal Circuitry Prohibits Double Pulse at
Either Output
˙Variable Dead Time Provides Control Over
Total Range
˙Internal Regulator Provides a Stable 5-V
Reference Supply With 5% Tolerance
˙Circuit Architecture Allows Easy Synchronization
Description
PLASTIC PACKAGE DIP-16
PLASTIC PACKAGE SO-16
The PL494 incorporates on a single monolithic chip all the
functions required in the construction of a pulse-width-
modulation control circuit.
Designed primarily for power supply control, this device
offers the systems engineer the flexibility to tailor the power
supply control circuitry to a specific application.
The PL494 contains two error amplifiers, an on-chip
adjustable oscillator, a dead-time control (DTC)
comparator , a pulse-steering control flip-flop, a 5-V, 5%-
precision regulator, and output-control circuits.
PIN CONNECTIONS
The error amplifiers exhibit a common-mode voltage range
from –0.3V to Vcc –2V.
The dead-time control comparator has a fixed offset that
provides approximately 5% dead time. The on-chip
oscillator may be bypassed by terminating RT to the
reference output and providing a sawtooth input to CT, or it
may drive the common circuits in synchronous multiple-rail
power supplies.
(TOP VIEW)
FUNCTION TABLE
INPUT TO OUTPUT CTRL
OUTPUT FUNCTION
VI=GND
VI=Vref
Single-ended or parallel output
Normal push-pull operation
PL494
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PL494 pdf, 반도체, 판매, 대치품
PL494
Revised Date : 2007/11/20
Page No. : 4/14
Electrical characteristics over recommended operating free-air temperature range, Vcc=15V,
f=10kHz (unless otherwise noted)
Reference section
PARAMETER
TEST CONDITIONS*
PL494CN
MIN TVP** MAX
Output voltage (REF)
IO=1mA
Input regulation
VCC=7V to 40V
Output regulation
IO=1mA to 10mA
Output voltage change with temperature ΔTA=MIN to MAX
4.75 5
2
1
2
5.25
25
15
10
Short-circuit output current***
REF= 0V
25
*For conditions shown as MIN or MAX, use the appropriate value specified under
recommended operating conditions.
**All typical values except for parameter changes with temperature are at TA=25°C.
***Duration of the short circuit should not exceed one second.
UNIT
V
mV
mV
mV/V
mA
Oscillator section, CT=0.01 mkF, RT=12kΩ
PARAMETER
TEST CONDITIONS*
PL494CN
MIN TVP**MAX
UNIT
Frequency
10 kHz
Standard deviation of frequency
All values of Vcc, CT, RT,and TA
constant
100
Hz/kHz
Frequency change with voltage Vcc=7V to 40V, TA=25°C
1 Hz/kHz
Frequency change with
temperature***
ΔTA=MIN to MAX
10 Hz/kHz
*For conditions shown as MIN or MAX, use the appropriate value specified under
recommended operating conditions.
**All typical values except for parameter changes with temperature are at TA=25°C.
***Temperature coefficient of timing capacitor and timing resistor not taken into account.
Error amplifier section
PARAMETER
Input offset voltage
Input offset current
TEST CONDITIONS
VO (FEEDBACK) = 2.5V
VO (FEEDBACK) = 2.5V
Input bias current
VO (FEEDBACK) = 2.5V
Common-mode input voltage
range
VCC = 7V to 40V
Open-loop voltage amplification ΔVO=3V, RL=2kΩ, VO=0.5V to 3.5V
Unity-gain bandwidth
VO=0.5V to 3.5V, RL=2kΩ
Common-mode rejection ratio ΔVO = 40V, TA=25°C
Output
sink
current
(FEEDBACK)
VID=-15mV to –5V,
V(FEEDBACK)=0.7V
Output source current
(FEEDBACK)
VID=15mV to 5V, V(FEEDBACK)=3.5V
*All typical values except for temperature coefficient are at TA=25°C
PL494CN
MIN TYP* MAX
UNIT
2 10 mV
25
250
nA
1 0.2 mkA
-0.3 to
VCC –2
V
70 95
dB
800 kHz
65 80
dB
0.3 0.7
mA
-2 mA
PL494
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PL494 전자부품, 판매, 대치품
PL494
Revised Date : 2007/11/20
Page No. : 7/14
APPLICATIONS INFORMATION
Description
The PL494CN is a fixed-frequency
pulse width modulation control circuit,
incorporating the primary building blocks
required for the control of a switching power
supply. (See Figure1.) An internal-linear
sawtooth oscillator is frequency-
programmable by two external components.
RT and CT. The Approximate oscillator
frequency is determined by:
For more information refer to Figure 3.
Output pulse width modulation
is
accomplished by comparison of the positive
sawtooth waveform across capacitor CT to
either of two control signals.
The NOR
gates, which drive output transistors Q1and
Q2, are enabled only when the flip-flop
clock-input line is in its low state. This
happens only during that portion of time
when the sawtooth voltage is greater than
the control signals. Therefore, an increase
in control-signal amplitude causes a
corresponding linear decrease of output
pulse width. (Refer to the Timing Diagram
shown in Figure2.)
The Control signals are external inputs
that can be fed into the deadtime control, the
error amplifier inputs, or the feedback input.
The deadtime control comparator has an
effective 120 mV input offset which limits the
minimum output deadtime to approximately
the first 4% of the sawtooth-cycle time. This
would result in a maximum duty cycle on a
given output of 96% with the output control
grounded, and 48% with it connected to the
reference line.
Additional deadtime
may be imposed on the output by setting the
deadtime-control input to a fixed voltage,
ranging between 0 V to 3.3 V.
adjust the output pulse width from the
maximum percent on-time, established by
the deadtime control input, down to zero, as
the voltage at the feedback pin varies from
0.5 V to 3.5 V. Both error amplifiers have a
common mode input range from -0.3 V to
(Vcc - 2V), and may be used to sense
power-supply output voltage and current.
The error-amplifier outputs are active high
and are ORed together at the noninverting
input of the pulse-width modulator
comparator. With this configuration, the
amplifier that demands minimum output on
time, dominates control of the loop.
When capacitor CT is discharged, a
positive pulse is generated on the output of
the deadtime comparator, which clocks the
pulse-steering flip-flop and inhibits the
output transistor, Q1 and Q2. With the
output-control connected to the reference
line, the pulse-steering flip-flop directs the
modulated pulses to each of the two output
transistors equal to half that of the oscillator.
Output drive can also be taken from Q1 or
Q2, when sinle-ended operation with a
maximum on-time of less than 50% is
required. This is desirable when the output
transformer has a ringback winding with a
catch diode used for snubbing. When
higher operation, Q1 and Q2 may be
connected in parallel, and the output-mode
pin must be tied to ground to disable the flip-
flop. The output frequency will now be
equal to that of the oscillator.
The PL494CN has an internal 5.0 V
reference capable of sourcing up to 10 mA
of load current for external bias circuits. The
reference has an internal accuracy of
±5.0% with a typical thermal drift of less than
50 mV over an operating temperature range
of 0°to 70.
The pulse width modulator comparator
provides a means for the error amplifiers to
PL494
Ω
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