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UC3845のメーカーはFairchild Semiconductorです、この部品の機能は「(UC3842 - UC3845) SMPS Controller」です。 |
部品番号 | UC3845 |
| |
部品説明 | (UC3842 - UC3845) SMPS Controller | ||
メーカ | Fairchild Semiconductor | ||
ロゴ | |||
このページの下部にプレビューとUC3845ダウンロード(pdfファイル)リンクがあります。 Total 12 pages
www.fairchildsemi.com
UC3842/UC3843/UC3844/UC3845
SMPS Controller
Features
• Low Start up Current
• Maximum Duty Clamp
• UVLO With Hysteresis
• Operating Frequency up to 500KHz
Internal Block Diagram
Description
The UC3842/UC3843/UC3844/UC3845 are fixed
frequencycurrent-mode PWM controller. They are specially
designed for Off-Line and DC to DC converter applications
with minimum external components. These integrated
circuits feature a trimmed oscillator for precise duty cycle
control, a temperature compensated reference, high gain
error amplifier, current sensing comparator and a high
current totempole output for driving a Power MOSFET. The
UC3842 and UC3844 have UVLO thresholds of 16V (on)
and 10V (off). The UC3843 and UC3845 are 8.5V(on) and
7.9V (off). The UC3842 and UC3843 can operate within
100% duty cycle. The UC3844 and UC3845 can operate
with 50% duty cycle.
8-DIP
8-SOP
1
14-SOP
1
1
* NORMALLY 8DIP/8SOP PIN NO.
* ( ) IS 14SOP PINNO.
* TOGGLE FLIP FLOP USED ONLY IN UC3844, UC3845
©2002 Fairchild Semiconductor Corporation
Rev. 1.0.1
1 Page UC3842/UC3843/UC3844/UC3845
Electrical Characteristics
(VCC=15V, RT=10kΩ, CT=3.3nF, TA= 0°C to +70°C, unless otherwise specified)
Parameter
Symbol
Conditions
REFERENCE SECTION
Reference Output Voltage
VREF TJ = 25°C, IREF = 1mA
Line Regulation
∆VREF 12V ≤ VCC ≤ 25V
Load Regulation
∆VREF 1mA ≤ IREF ≤ 20mA
Short Circuit Output Current
ISC TA = 25°C
OSCILLATOR SECTION
Oscillation Frequency
f TJ = 25°C
Frequency Change with
Voltage
∆f/∆VCC 12V ≤ VCC ≤ 25V
Oscillator Amplitude
VOSC
-
ERROR AMPLIFIER SECTION
Input Bias Current
IBIAS
-
Input Voltage
VI(E>A) Vpin1 = 2.5V
Open Loop Voltage Gain
GVO
2V ≤ VO ≤ 4V (Note3)
Power Supply Rejection Ratio PSRR 12V ≤ VCC ≤ 25V (Note3)
Output Sink Current
ISINK Vpin2 = 2.7V, Vpin1 = 1.1V
Output Source Current
ISOURCE Vpin2 = 2.3V, Vpin1 = 5V
High Output Voltage
VOH
Vpin2 = 2.3V, RL = 15kΩ to GND
Low Output Voltage
VOL Vpin2 = 2.7V, RL = 15kΩ to Pin 8
CURRENT SENSE SECTION
Gain
GV (Note 1 & 2)
Maximum Input Signal
VI(MAX)
Power Supply Rejection Ratio PSRR
Vpin1 = 5V(Note 1)
12V ≤ VCC ≤ 25V (Note 1,3)
Input Bias Current
IBIAS
-
OUTPUT SECTION
Low Output Voltage
VOL
ISINK = 20mA
ISINK = 200mA
High Output Voltage
VOH
ISOURCE = 20mA
ISOURCE = 200mA
Rise Time
tR TJ = 25°C, CL= 1nF (Note 3)
Fall Time
tF TJ = 25°C, CL= 1nF (Note 3)
UNDER-VOLTAGE LOCKOUT SECTION
Start Threshold
UC3842/UC3844
VTH(ST)
UC3843/UC3845
Min. Operating Voltage
(After Turn On)
UC3842/UC3844
VOPR(MIN)
UC3843/UC3844
Min. Typ. Max. Unit
4.90 5.00 5.10 V
- 6 20 mV
- 6 25 mV
- -100 -180 mA
47 52 57 kHz
- 0.05 1
%
- 1.6 - VP-P
- -0.1 -2 µA
2.42 2.50 2.58 V
65 90 - dB
60 70 - dB
2 7 - mA
-0.6 -1.0 - mA
5 6 -V
- 0.8 1.1 V
2.85 3 3.15 V/V
0.9 1 1.1 V
- 70 - dB
- -3 -10 µA
- 0.08 0.4 V
- 1.4 2.2 V
13 13.5 -
V
12 13.0 -
V
- 45 150 ns
- 35 150 ns
14.5 16.0 17.5
7.8 8.4 9.0
8.5 10.0 11.5
7.0 7.6 8.2
V
V
V
V
3
3Pages UC3842/UC3843/UC3844/UC3845
Figure 5. Oscillator Waveforms and Maximum Duty Cycle
Oscillator timing capacitor, CT, is charged by VREF through RT and discharged by an internal current source. During the
discharge time, the internal clock signal blanks the output to the low state. Selection of RT and CT therefore determines both
oscillator frequency and maximum duty cycle. Charge and discharge times are determined by the formulas:
tc = 0.55 RT CT
tD=
RT
CTI
n
-0--0-.--0.--0-0--0-6---6-3--3-R---R--T--T--–---–--2--4-.--7-
Frequency, then, is: f=(tc + td)-1
ForRT > 5KΩ,f= ----1---.--8-----
RTCT
Figure 6. Oscillator Dead Time & Frequency
(Deadtime vs CT RT > 5kΩ)
Figure 7. Timing Resistance vs Frequency
Figure 8. Shutdown Techniques
6
6 Page | |||
ページ | 合計 : 12 ページ | ||
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PDF ダウンロード | [ UC3845 データシート.PDF ] |
データシートを活用すると、その部品の主な機能と仕様を詳しく理解できます。 ピン構成、電気的特性、動作パラメータ、性能を確認してください。 |
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