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| 型号： | CS5171EDR8 |
| 厂商： | ON Semiconductor |
| 文件页数： | 10/21页 |
| 文件大小： | 0K |
| 描述： | IC REG MULTI CONFIG 1.5A 8SOIC |
| 产品变化通告： | Product Discontinuation 27/Jun/2007 |
| 标准包装： | 1 |
| 类型： | 升压（升压），回扫，正向转换器，Sepic |
| 输出数： | 1 |
| 输入电压： | 2.7 V ~ 30 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 280kHz |
| 电流 - 输出： | 1.5A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 剪切带 (CT) |
| 供应商设备封装： | 8-SOICN |
| 其它名称： | CS5171EDR8OSCT |
CS5171, CS5172, CS5173, CS5174
APPLICATIONS INFORMATION
THEORY OF OPERATION
Current Mode Control
The oscillator is trimmed to guarantee an 18% frequency
accuracy. The output of the oscillator turns on the power
switch at a frequency of 280 kHz (CS5171/2) or 560 kHz
V C
Oscillator
?
+
PWM
Comparator
SUMMER
Slope Compensation
S
R
Q
X5
Power Switch
In Out
Driver
63 m W
V SW
V CC
L
D1
C O
R LOAD
(CS5173/4), as shown in Figure 27. The power switch is
turned off by the output of the PWM Comparator.
A TTL ? compatible sync input at the SS pin is capable of
syncing up to 1.8 times the base oscillator frequency. As
shown in Figure 28, in order to sync to a higher frequency,
a positive transition turns on the power switch before the
output of the oscillator goes high, thereby resetting the
oscillator. The sync operation allows multiple power
supplies to operate at the same frequency.
A sustained logic low at the SS pin will shut down the IC
Figure 27. Current Mode Control Scheme
The CS517x family incorporates a current mode control
scheme, in which the PWM ramp signal is derived from the
power switch current. This ramp signal is compared to the
output of the error amplifier to control the on ? time of the
power switch. The oscillator is used as a fixed ? frequency
clock to ensure a constant operational frequency. The
resulting control scheme features several advantages over
conventional voltage mode control. First, derived directly
from the inductor, the ramp signal responds immediately to
line voltage changes. This eliminates the delay caused by the
output filter and error amplifier, which is commonly found
and reduce the supply current.
An additional feature includes frequency shift to 20% of
the nominal frequency when either the NFB or FB pins
trigger the threshold. During power up, overload, or short
circuit conditions, the minimum switch on ? time is limited
by the PWM comparator minimum pulse width. Extra
switch off ? time reduces the minimum duty cycle to protect
external components and the IC itself.
As previously mentioned, this block also produces a ramp
for the slope compensation to improve regulator stability.
Error Amplifier
2.0 V
?
Voltage
1.276 V +
?
positive error ? amp
in voltage mode controllers. The second benefit comes from
inherent pulse ? by ? pulse current limiting by merely
clamping the peak switching current. Finally, since current
mode commands an output current rather than voltage, the
filter offers only a single pole to the feedback loop. This
allows both a simpler compensation and a higher
gain ? bandwidth over a comparable voltage mode circuit.
Without discrediting its apparent merits, current mode
control comes with its own peculiar problems, mainly,
subharmonic oscillation at duty cycles over 50%. The
CS517x family solves this problem by adopting a slope
200 k
250 k
NFB +
CS5172/4
negative error ? amp
120 pF
1M W
Clamp
FB
CS5171/3
Figure 29. Error Amplifier Equivalent Circuit
V C
C1
0.01 m F
R1
5 k W
compensation scheme in which a fixed ramp generated by
the oscillator is added to the current ramp. A proper slope
rate is provided to improve circuit stability without
sacrificing the advantages of current mode control.
Oscillator and Shutdown
Sync
Current
Ramp
V SW
Figure 28. Timing Diagram of Sync and Shutdown
For CS5172/4, the NFB pin is internally referenced to
? 2.5 V with approximately a 250 k W input impedance. For
CS5171/3, the FB pin is directly connected to the inverting
input of the positive error amplifier, whose non ? inverting
input is fed by the 1.276 V reference. Both amplifiers are
transconductance amplifiers with a high output impedance
of approximately 1 M W , as shown in Figure 29. The V C pin
is connected to the output of the error amplifiers and is
internally clamped between 0.5 V and 1.7 V. A typical
connection at the V C pin includes a capacitor in series with
a resistor to ground, forming a pole/zero for loop
compensation.
An external shunt can be connected between the V C pin
and ground to reduce its clamp voltage. Consequently, the
current limit of the internal power transistor current is
reduced from its nominal value.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| CS5171EDR8G | 功能描述:直流/直流开关调节器 1.5A High Efficiency Boost RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
| CS5171GD8 | 功能描述:直流/直流开关调节器 1.5A High Efficiency RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
| CS5171GD8G | 功能描述:直流/直流开关调节器 1.5A High Efficiency Boost RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
| CS5171GDR8 | 功能描述:直流/直流开关调节器 1.5A High Efficiency RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
| CS5171GDR8G | 功能描述:直流/直流开关调节器 1.5A High Efficiency Boost RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
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