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PDF ML4823 Data sheet ( Hoja de datos )
| Número de pieza | ML4823 | |
| Descripción | High Frequency Power Supply Controller | |
| Fabricantes | Micro Linear | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de ML4823 (archivo pdf) en la parte inferior de esta página. Total 9 Páginas | ||
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May 1997
ML4823*
High Frequency Power Supply Controller
GENERAL DESCRIPTION
The ML4823 High Frequency PWM Controller is an IC
controller optimized for use in Switch Mode Power
Supply designs running at frequencies to 1MHz.
Propagation delays are minimal through the comparators
and logic for reliable high frequency operation while slew
rate and bandwidth are maximized on the error amplifier.
This controller is designed for single-ended applications
using voltage or current mode and provides for input
voltage feed forward.
A 1V threshold current limit comparator provides cycle-
by-cycle current limit and exceeding a 1.4V threshold
initiates a soft-start cycle. The soft start pin doubles as a
maximum duty cycle clamp. All logic is fully latched to
provide jitter-free operation and prevent multiple pulsing.
An under-voltage lockout circuit with 800mV of hysteresis
assures low startup current and drives the outputs low
during fault conditions.
This controller is an improved second source for the
UC3823 controller; however, the ML4823 includes
features not found on the 3823. These features are set in
italics.
FEATURES
s Practical operation at switching frequencies to 1.0MHz
s High current (2A peak) totem pole output
s Wide bandwidth error amplifier
s Fully latched logic with double pulse suppression
s Pulse-by-pulse current limiting
s Soft start and max. duty cycle control
s Under voltage lockout with hysteresis
s 5.1V trimmed bandgap reference
s Low start-up current (1.1mA)
s Pin compatible improved replacement for UC3823
s Fast shut down path from current limit to output
s Soft start latch ensures full soft start cycle
s Outputs pull low for undervoltage lockout
*Some Packages Are Obsolete
BLOCK DIAGRAM (Pin Configuration Shown for 16-Pin Version)
5 RT
6 CT
OSC
CLOCK OUT
4
RAMP
7
1.25V
+
E/A OUT
3
NI
2
INV
1
+
ERROR
AMP
–
SOFT START
8
11 ILIM REF
9 ILIM/S.D.
–
+
+
1.4V –
+
COMP
–
V+
–
+ 1V
R
Q
S
R
Q
S
– 4V
+
5.1V
ENABLE
VREF
VREF GEN
– 9V
UNDER +
VOLTAGE
LOCKOUT
INTERNAL
BIAS
POWER VC 13
OUTPUT 14
POWER GND 12
5.1V VREF 16
VCC 15
SIGNAL GND 10
1
1 page  
FUNCTIONAL DESCRIPTION
OSCILLATOR
The ML4823 oscillator charges the external capacitor (CT)
with a current (ISET) equal to 3/RSET. When the capacitor
voltage reaches the upper threshold (Ramp Peak), the
comparator changes state and the capacitor discharges to
the lower threshold (Ramp Valley) through Q1. While the
capacitor is discharging, Q2 provides a high pulse.
ML4823
The oscillator period can be described by the following
relationship:
TOSC = TRAMP + TDEADTIME
where: TRAMP = C (Ramp Valley to Peak)/ISET
and: TDEADTIME = C (Ramp Valley to Peak)/IQ1
ISET
RT
RT
3V
CT
IQ1
Q1
5.1V
ISET
+
Q2
– CLOCK
OUT
400µA
CLOCK OUT
RAMP PEAK
CT
RAMP VALLEY
TD
Figure 1. Oscillator Block Diagram
100k
100nF
47nF
22nF
10nF
10k
4.7nF
2.2nF
1nF
470pF
1k
0.1k 1k 10k 100k 1M 10M
FREQ (Hz)
Figure 2. Oscillator Timing Resistance vs Frequency
160
140
120
100
80
10k
1.0nF
470pF
100k
FREQ (Hz)
1M
Figure 3. Oscillator Deadtime vs Frequency
30
25
20
15
10
5
0
0.47 1.0 2.2 4.7 10.0 22 47 100
CT (nF)
Figure 4. Oscillator Deadtime vs CT (3kΩ ≤ RT ≤ 100kΩ)
5
5 Page | ||
| Páginas | Total 9 Páginas | |
| PDF Descargar | [ Datasheet ML4823.PDF ] | |
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