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| 型号： | UC2845BDR2 |
| 厂商： | ON Semiconductor |
| 文件页数： | 9/19页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR PWM CM 14-SOIC |
| 产品变化通告： | LTB Notification 03/Jan/2008 |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 275kHz |
| 占空比： | 50% |
| 电源电压： | 7.6 V ~ 30 V |
| 降压： | 无 |
| 升压： | 是 |
| 回扫： | 是 |
| 反相： | 是 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 是 |
| 工作温度： | -25°C ~ 85°C |
| 封装/外壳： | 14-SOIC（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
UC3844B, UC3845B, UC2844B, UC2845B
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 built ? in
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 off ? line converter applications where
efficient bootstrap startup techniques are required
(Figure 30). The UCX845B is intended for lower voltage
dc ? dc 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 SOIC ? 14 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
V ref
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 current ? sensing
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
short ? circuit 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
wire ? wrap or plug ? in prototype boards. High frequency
circuit layout techniques are imperative to prevent
pulse ? width jitter. This is usually caused by excessive noise
pick ? up 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 low ? current signal and
high ? current switch and output grounds returning on
separate paths back to the input filter capacitor. Ceramic
bypass capacitors (0.1 m 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 noise ? generating components.
8(14)
R
8(14)
R
R T
R
Bias
R A
8
4
R
Bias
Osc
R B
6
5.0k
3
Osc
External
Sync
0.01
C T
47
4(7)
2(3)
EA
+
2R
R
C
5
2
5.0k
5.0k
R
Q
S
MC1455
7
4(7)
2(3)
EA
+
2R
R
Input
1(1)
1
1(1)
5(9)
To Additional
UCX84XBs
5(9)
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.
f +
1.44
(RA ) 2RB)C
D(max) +
RA
RA ) 2RB
Figure 18. External Clock Synchronization
Figure 19. External Duty Cycle Clamp and
Multi ? Unit Synchronization
http://onsemi.com
9
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相关代理商/技术参数 |
参数描述 |
|---|---|
| UC2845BDR2G | 功能描述:电流型 PWM 控制器 52kHz 1A Current PWM w/48% Duty Cycle Max RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| UC2845BG | 制造商:ONSEMI 制造商全称:ON Semiconductor 功能描述:HIGH PERFORMANCE CURRENT MODE CONTROLLERS |
| UC2845BL | 制造商:ONSEMI 制造商全称:ON Semiconductor 功能描述:HIGH PERFORMANCE CURRENT MODE CONTROLLERS |
| UC2845BN | 功能描述:电流型 PWM 控制器 0.5mA Current Mode RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| UC2845BNG | 功能描述:电流型 PWM 控制器 ANA SMPS PWM CONTROLLER RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
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