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| 型号： | FAN5236MTCX |
| 厂商： | Fairchild Semiconductor |
| 文件页数： | 12/19页 |
| 文件大小： | 0K |
| 描述： | IC CTLR DDR/PWM DUAL HE 28TSSOP |
| 产品变化通告： | Mold Compound Change 30/Nov/2007 |
| 标准包装： | 1 |
| 应用： | 控制器，移动式 DDR |
| 输入电压： | 5 V ~ 24 V |
| 输出数： | 2 |
| 输出电压： | 0.9 V ~ 5 V |
| 工作温度： | -10°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-TSSOP（0.173"，4.40mm 宽） |
| 供应商设备封装： | 28-TSSOP |
| 包装： | 标准包装 |
| 产品目录页面： | 1221 (CN2011-ZH PDF) |
| 其它名称： | FAN5236MTCXDKR |
A transition back to PWM continuous conduction mode
(CCM) mode occurs when the inductor current rises
sufficiently to stay positive for eight consecutive cycles.
This occurs when:
Because of the different control mechanisms, the value
of the load current where transition into CCM operation
takes place is typically higher compared to the load
level at which transition into Hysteretic Mode occurs.
I LOAD ( CCM ) = ?
? Δ V HYSTERESIS ?
? 2 ESR ?
?
(3)
Hysteretic Mode can be disabled by setting the FPWM
pin LOW.
where Δ V HYSTERESIS = 15mV and ESR is the equivalent
series resistance of C OUT .
Figure 12.
Current Processing Section
Current Limit / Summing Circuits
R SENSE = ? ?
? 100 ? ?
? I LOAD ( MAX ) ? R DS ( ON ) ?
(4)
?
?
The current through the R SENSE resistor (I SNS ) is
sampled (typically 400ns) after Q2 is turned on, as
shown in Figure 12. That current is held and summed
with the output of the error amplifier. This effectively
creates a current-mode control loop. The resistor
connected to ISNSx pin (R SENSE ) sets the gain in the
current feedback loop. The following expression
estimates the recommended value of R SENSE as a
function of the maximum load current (I LOAD(MAX) ) and
the value of the MOSFET R DS(ON) :
75 μA
R SENSE must, however, be kept higher than 700 Ω even if
the number calculated comes out to be less than 700 Ω .
Setting the Current Limit
Since the tolerance on the current limit is largely
dependent on the ratio of the external resistors, it is
fairly accurate if the voltage drop on the switching-node
side of R SENSE is an accurate representation of the load
current. When using the MOSFET as the sensing
element, the variation of R DS(ON) causes proportional
variation in the I SNS . This value varies from device to
device and has a typical junction temperature
coefficient of about 0.4%/°C (consult the MOSFET
datasheet for actual values), so the actual current limit
set point decreases proportional to increasing MOSFET
die temperature. A factor of 1.6 in the current limit set
point should compensate for MOSFET R DS(ON)
variations, assuming the MOSFET heat sinking keeps
its operating die temperature below 125°C.
Q2
A ratio of I SNS is compared to the current established
when a 0.9V internal reference drives the ILIM pin:
LDRV
ISNS
R SENSE
? ( 100 + R
SENSE ) ?
?
? ?
x ?
?
?
R LIM =
11
I LOAD
? R DS ( ON )
?
(5)
PGND
? 2002 Fairchild Semiconductor Corporation
Figure 13.
Improving Current-Sensing Accuracy
www.fairchildsemi.com
FAN5236 ? Rev. 1.3.2
12
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相关代理商/技术参数 |
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|---|---|
| FAN5236QSC | 功能描述:开关变换器、稳压器与控制器 DC/DC RoHS:否 制造商:Texas Instruments 输出电压:1.2 V to 10 V 输出电流:300 mA 输出功率: 输入电压:3 V to 17 V 开关频率:1 MHz 工作温度范围: 安装风格:SMD/SMT 封装 / 箱体:WSON-8 封装:Reel |
| FAN5236QSC_Q | 功能描述:开关变换器、稳压器与控制器 DC/DC RoHS:否 制造商:Texas Instruments 输出电压:1.2 V to 10 V 输出电流:300 mA 输出功率: 输入电压:3 V to 17 V 开关频率:1 MHz 工作温度范围: 安装风格:SMD/SMT 封装 / 箱体:WSON-8 封装:Reel |
| FAN5236QSCX | 功能描述:开关变换器、稳压器与控制器 PWM Controller RoHS:否 制造商:Texas Instruments 输出电压:1.2 V to 10 V 输出电流:300 mA 输出功率: 输入电压:3 V to 17 V 开关频率:1 MHz 工作温度范围: 安装风格:SMD/SMT 封装 / 箱体:WSON-8 封装:Reel |
| FAN5240 | 制造商:FAIRCHILD 制造商全称:Fairchild Semiconductor 功能描述:Multi-Phase PWM Controller for AMD Mobile Athlon TM and Duron TM |
| FAN5240_06 | 制造商:FAIRCHILD 制造商全称:Fairchild Semiconductor 功能描述:Multi-Phase PWM Controller for AMD Mobile Athlon and Duron |
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