参数资料
| 型号： | UCC28250RGPT |
| 厂商： | Texas Instruments |
| 文件页数： | 17/53页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR PWM CM/VM 20-QFN |
| 标准包装： | 1 |
| PWM 型： | 电流/电压模式 |
| 输出数： | 1 |
| 频率 - 最大： | 1MHz |
| 占空比： | 100% |
| 电源电压： | 4.7 V ~ 17 V |
| 降压： | 无 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 封装/外壳： | 20-VFQFN 裸露焊盘 |
| 包装： | 标准包装 |
| 其它名称： | 296-27777-6 |
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SLUSA29C – APRIL 2010 – REVISED JULY 2011
RAMP/CS (PWM Ramp Input or Current Sense Input) (16/3)
The UCC28250 can be controlled using either voltage mode or current mode. RAMP/CS is a multi-function pin
used either to generate the ramp signal for voltage mode control or to sense current for current mode control.The
following sections describe the RAMP/CS functionality for voltage mode and current mode control.
RAMP: Voltage Mode Control with Feed-Forward Operation
For voltage mode control, a resistor R CS and a capacitor C CS must be connected to the RAMP/CS pin as shown
in Figure 11 . The internal pull-down switch has approximately 40- Ω on-resistance. The RAMP/CS pin is clamped
internally to 4 V for internal device protection. The C CS value must be small enough to discharge the RAMP/CS
pin from its peak voltage to ground within the pulse width of the BLANK signal (T D(sp) + 70 ns). The following
formula derives a C CS value.
C CS < ? ÷ ′ d(SP)
40 W
è ?
?4V/2? T +70ns
4V
(4)
A C CS value less than 650 pF works for most applications. In order to minimize the impacts of parasitic
capacitance caused by the PCB layout and routing, a minimum of 100 pF is recommended for C CS . Once C CS is
determined, R CS can be calculated according to the desired ramp peak amplitude.
è V CHARGE PK
2 ′ ln ?
R CS =
? V CHARGE
1
- V
?
÷ ′ C CS ′ f SW
?
(5)
In this equation, the V CHARGE is the voltage used to generate the ramp, V PK is the desired ramp amplitude and
the f SW is the switching frequency.
Choose the ramp amplitude to accommodate the voltage range of the COMP pin and the maximum duty cycle
required by the power stage. Use the following equation to select V PK , in the equation, D MAX is the maximum duty
cycle for primary outputs.
V PK =
1.4 V
D MAX
R CS
UCC28250
VREF
RAMP/CS
V IN 36 V to 75 V
R CS
UCC28250
RAMP/CS
(6)
C CS
GND
BLANK
C CS
GND
BLANK
Figure 11. Fixed Ramp Generation/Ramp Generation With Input Voltage Feedforward
Voltage feed-forward can be achieved by driving R CS from line input VIN. The peak of RAMP/CS is proportional
to VIN and output has have much faster line transient response. When the UCC28250 is used for the
primary-side control, RAMP parameters are critical for the optimal pre-biased start up performance. Refer to the
‘ Voltage Mode Control and Input Voltage Feed-Forward ’ section of the Functional Description section for a
detailed design procedure of choosing R CS .
If the line input cannot be easily accessed due to limited board area or other limitation, a RAMP signal with fixed
peak voltage can be implemented by simply driving R CS from 3.3 V VREF ( Figure 11 ).
Copyright ? 2010 – 2011, Texas Instruments Incorporated
Product Folder Link(s): UCC28250
17
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相关代理商/技术参数 |
参数描述 |
|---|---|
| UCC28250RGPT | 制造商:Texas Instruments 功能描述:PWM CONTROLLER IC 17V QFN-20 制造商:Texas Instruments 功能描述:IC, PWM CONTROLLER, 17V, QFN-20 |
| UCC28251 | 制造商:TI 制造商全称:Texas Instruments 功能描述:Advanced PWM Controller With Pre-Bias Operation |
| UCC28251PW | 功能描述:电压模式 PWM 控制器 Advanced PWM Cntlr RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
| UCC28251PWR | 功能描述:电压模式 PWM 控制器 Advanced PWM Cntlr RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
| UCC28251PWT | 制造商:TI 制造商全称:Texas Instruments 功能描述:Advanced PWM Controller With Pre-Bias Operation |
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