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CS52845 데이터시트 PDF




Cherry Semiconductor Corporation에서 제조한 전자 부품 CS52845은 전자 산업 및 응용 분야에서
광범위하게 사용되는 반도체 소자입니다.


PDF 형식의 CS52845 자료 제공

부품번호 CS52845 기능
기능 Current Mode PWM Control Circuit with 50% Max Duty Cycle
제조업체 Cherry Semiconductor Corporation
로고 Cherry Semiconductor Corporation 로고


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CS52845 데이터시트, 핀배열, 회로
CS52845
Current Mode PWM Control Circuit
with 50% Max Duty Cycle
Description
The CS52845 provides all the nec-
essary features to implement off-
line fixed frequency current-mode
control with a minimum number
of external components.
The CS52845 incorporates a new
precision temperature-controlled
oscillator to minimize variations in
frequency. An internal toggle flip-
flop, which blanks the output
every other clock cycle, limits the
duty-cycle range to less than 50%.
An undervoltage lockout ensures
that VREF is stabilized before the
output stage is enabled. In the
CS52845 turn on is at 8.4V and
turn off at 7.6V.
Other features include low start-up
current, pulse-by-pulse current lim-
iting, and a high-current totem pole
output for driving capacitive loads,
such as gate of a power MOSFET.
The output is low in the off state,
consistent with N-channel devices.
Absolute Maximum Ratings
Supply Voltage (ICC<30mA) ..........................................................Self Limiting
Supply Voltage (Low Impedance Source)...................................................30V
Output Current ...............................................................................................±1A
Output Energy (Capacitive Load) .................................................................5µJ
Analog Inputs (VFB, VSENSE)...........................................................-0.3V to 5.5V
Error Amp Output Sink Current...............................................................10mA
Lead Temperature Soldering
Reflow (SMD styles only) ...........60 sec. max above 183°C, 230°C peak
Block Diagram
VCC VCC Undervoltage Lock-out
34V
Gnd
VFB
COMP
OSC
Sense
8.4V/7.6V
Set/ 5.0 Volt
Reset Reference
Error
Amplifier
-
+
2.50V
Oscillator
VREF
R Undervoltage
Lockout
R
Toggle
Flip-Flop
2R
R
S
R
1V
Current PWM
Sensing Latch
Comparator
NOR
Internal
Bias
VCC Pwr
VREF
VOUT
Pwr Gnd
Features
s Optimized for Off-line
Control
s Temperature
Compensated Oscillator
s 50% Maximum Duty-cycle
Clamp
s VREF Stabilized before
Output Stage is Enabled
s Low Start-up Current
s Pulse-by-pulse Current
Limiting
s Improved Undervoltage
Lockout
s Double Pulse Suppression
s 1% Trimmed Bandgap
Reference
s High Current Totem Pole
Output
Package Options
8L SO Narrow
COMP 1
VFB 2
Sense 3
OSC 4
8 VREF
7 VCC
6 VOUT
5 Gnd
14L SO Narrow
COMP 1
NC 2
VFB 3
NC 4
Sense 5
NC 6
OSC 7
14 VREF
13 NC
12 VCC
11 VCC Pwr
10 VOUT
9 Gnd
8 Pwr Gnd
Rev. 3/4/99
Cherry Semiconductor Corporation
2000 South County Trail, East Greenwich, RI 02818
Tel: (401)885-3600 Fax: (401)885-5786
Web Site: www.cherry-semi.com
1
A Company
®




CS52845 pdf, 반도체, 판매, 대치품
Test Circuit Open Loop Laboratory Test Fixture
4.7k
1k
Error Amp
Adjust
4.7k
RT
2N2222
100k
COMP
5k
Sense
Adjust
VFB
Sense
OSC
VREF
VCC
V O UT
Gnd
CT
0.1µF
A
0.1µF
1k
1W
VREF
VCC
V O UT
Gnd
Circuit Description
Undervoltage Lockout
During Undervoltage Lockout (Figure 1), the output driv-
er is biased to sink minor amounts of current. The output
should be shunted to ground with a resistor to prevent
VCC
ON/OFF Command
activating the power switch with extraneous leakage cur-
to reset of IC
rents.
VON = 8.4V
VOFF = 7.6V
ICC
<15mA
<1mA
VON VOFF
Figure 1: Startup voltage for the CS52845.
PWM Waveform
To generate the PWM waveform, the control voltage from
the error amplifier is compared to a current sense signal
which represents the peak output inductor current (Figure
2). An increase in VCC causes the inductor current slope to
increase, thus reducing the duty cycle. This is an inherent
feed-forward characteristic of current mode control, since
the control voltage does not have to change during
changes of input supply voltage.
When the power supply sees a sudden large output cur-
rent increase, the control voltage will increase allowing
VCC the duty cycle to momentarily increase. Since the duty
cycle tends to exceed the maximum allowed to prevent
transformer saturation in some power supplies, the inter-
nal oscillator waveform provides the maximum duty cycle
clamp as programmed by the selection of OSC compo-
nents.
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