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參數(shù)資料
| 型號： | UC2845B |
| 廠商： | ON SEMICONDUCTOR |
| 英文描述： | High Performance Current Mode Controllers(高性能電流模式控制器) |
| 中文描述： | 高性能電流模式控制器（高性能電流模式控制器） |
| 文件頁數(shù)： | 9/18頁 |
| 文件大小： | 400K |
| 代理商： | UC2845B |
UC3844B, UC3845B, UC2844B, UC2845B
http://onsemi.com
9
Undervoltage Lockout
Two undervoltage lockout comparators have been
incorporated to guarantee that the IC is fully functional
before the output stage is enabled. The positive power
supply terminal (V
CC
) and the reference output (V
ref
) are
each monitored by separate comparators. Each has builtin
hysteresis to prevent erratic output behavior as their
respective thresholds are crossed. The V
CC
comparator
upper and lower thresholds are 16 V/10 V for the UCX844B,
and 8.4 V/7.6 V for the UCX845B. The V
ref
comparator
upper and lower thresholds are 3.6 V/3.4 V. The large
hysteresis and low startup current of the UCX844B makes
it ideally suited in offline converter applications where
efficient bootstrap startup techniques are required
(Figure 30). The UCX845B is intended for lower voltage
dcdc converter applications. A 36 V Zener is connected as
a shunt regulator from V
CC
to ground. Its purpose is to
protect the IC from excessive voltage that can occur during
system startup. The minimum operating voltage for the
UCX844B is 11 V and 8.2 V for the UCX845B.
Output
These devices contain a single totem pole output stage that
was specifically designed for direct drive of power
MOSFETs. It is capable of up to
±
1.0 A peak drive current
and has a typical rise and fall time of 50 ns with a 1.0 nF load.
Additional internal circuitry has been added to keep the
Output in a sinking mode whenever an undervoltage lockout
is active. This characteristic eliminates the need for an
external pulldown resistor.
The SOIC14 surface mount package provides separate
pins for V
C
(output supply) and Power Ground. Proper
implementation will significantly reduce the level of
switching transient noise imposed on the control circuitry.
This becomes particularly useful when reducing the I
pk(max)
clamp level. The separate V
C
supply input allows the
designer added flexibility in tailoring the drive voltage
independent of V
CC
. A Zener clamp is typically connected
to this input when driving power MOSFETs in systems
where V
CC
is greater than 20 V. Figure 23 shows proper
power and control ground connections in a currentsensing
power MOSFET application.
Reference
The 5.0 V bandgap reference is trimmed to
±
1.0%
tolerance at T
J
= 25
°
C on the UC284XB, and
±
2.0% on the
UC384XB. Its primary purpose is to supply charging current
to the oscillator timing capacitor. The reference has
shortcircuit protection and is capable of providing in
excess of 20 mA for powering additional control system
circuitry.
Design Considerations
Do not attempt to construct the converter on
wirewrap or plugin prototype boards.
High frequency
circuit layout techniques are imperative to prevent
pulsewidth jitter. This is usually caused by excessive noise
pickup imposed on the Current Sense or Voltage Feedback
inputs. Noise immunity can be improved by lowering circuit
impedances at these points. The printed circuit layout should
contain a ground plane with lowcurrent signal and
highcurrent switch and output grounds returning on
separate paths back to the input filter capacitor. Ceramic
bypass capacitors (0.1 F) connected directly to V
CC
, V
C
,
and V
ref
may be required depending upon circuit layout.
This provides a low impedance path for filtering the high
frequency noise. All high current loops should be kept as
short as possible using heavy copper runs to minimize
radiated EMI. The Error Amp compensation circuitry and
the converter output voltage divider should be located close
to the IC and as far as possible from the power switch and
other noisegenerating components.
Bias
+
Osc
R
R
R
2R
EA
5(9)
1(1)
2(3)
4(7)
8(14)
R
T
C
T
V
ref
Figure 18. External Clock Synchronization
Figure 19. External Duty Cycle Clamp and
MultiUnit Synchronization
0.01
The diode clamp is required if the Sync amplitude is large enough to cause
the bottom side of C
T
to go more than 300 mV below ground.
External
Sync
Input
47
+
R
R
R
2R
Bias
Osc
EA
5(9)
1(1)
2(3)
4(7)
8(14)
To Additional
UCX84XBs
R
S
Q
8
4
6
5
2
1
C
3
7
R
A
R
B
5.0k
5.0k
5.0k
MC1455
f
1.44
2RB)C
(RA
D(max)
RA
RA
2RB
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PDF描述 |
|---|---|
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| UC2845BAC | 制造商:ONSEMI 制造商全稱:ON Semiconductor 功能描述:HIGH PERFORMANCE CURRENT MODE CONTROLLERS |
| UC2845BD | 功能描述:電流型 PWM 控制器 52kHz 1A Current PWM RoHS:否 制造商:Texas Instruments 開關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| UC2845BD1 | 功能描述:電流型 PWM 控制器 0.5mA Current Mode RoHS:否 制造商:Texas Instruments 開關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| UC2845BD1013TR | 功能描述:電流型 PWM 控制器 0.5mA Current Mode RoHS:否 制造商:Texas Instruments 開關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| UC2845BD1G | 功能描述:電流型 PWM 控制器 52kHz 1A Current PWM w/48% Duty Cycle Max RoHS:否 制造商:Texas Instruments 開關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
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