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| 型号： | FAN5234MTCX |
| 厂商： | Fairchild Semiconductor |
| 文件页数： | 8/15页 |
| 文件大小： | 0K |
| 描述： | IC PWM CTLR/PFM MOBILE 16TSSOP |
| 标准包装： | 1 |
| 应用： | 控制器，移动式个人电脑 |
| 输入电压： | 2 V ~ 24 V |
| 输出数： | 1 |
| 输出电压： | 0.9 V ~ 5.5 V |
| 工作温度： | -10°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-TSSOP（0.173"，4.40mm 宽） |
| 供应商设备封装： | 16-TSSOP |
| 包装： | 标准包装 |
| 其它名称： | FAN5234MTCXDKR |
V CORE
I L
0
PWMMode
HystereticMode
1
2
3
4
5
6
7
8
V CORE
I L
0
1
2
HystereticMode
3
4
5
6
7
8
PWMMode
Figure 4. Transitioning between PWM and Hysteretic Mode
The hysteretic comparator causes HDRV turn-on when
the output voltage (at V SEN ) falls below the lower
threshold (10mV below V REF ) and terminates the PFM
signal when V SEN rises over the higher threshold (5mV
above V REF ).
Setting the Current Limit
A ratio of I SNS is also compared to the current
established when a 0.9V internal reference drives the
ILIM pin:
? ( 100 + R
?
SENSE ) ?
x ? ?
?
?
The switching frequency is primarily a function of:
Spread between the two hysteretic thresholds
R LIM =
11
I LOAD
? R DS ( ON ) ?
?
(5)
I LOAD ( CCM ) = ?
? Δ V HYSTERESIS ?
I LOAD
Output inductor and capacitor ESR
A transition back to PWM Continuous Conduction Mode
or (CCM) occurs when the inductor current rises
sufficiently to stay positive for eight consecutive cycles.
This occurs when:
? (3)
? 2 ESR ?
where Δ V HYSTERESIS = 15mV and ESR is the equivalent
series resistance of C OUT .
Due to different control mechanisms, the value of the
load current where transition into PWM operation takes
place is typically higher compared to the load level at
which transition into Hysteretic Mode occurs. Hysteretic
Mode can be disabled by setting the FPWM pin HIGH.
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 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) , 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 all MOSFET R DS(ON) variations,
assuming the MOSFET’s heat sinking keep its
operating die temperature below 125°C.
Q2
LDRV
Current Processing
The following discussion refers to Figure 6.
The current through R SENSE resistor (I SNS ) is sampled
shortly after Q2 is turned on. 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 the ISNS pin (R SENSE ) sets the
gain in the current feedback loop. Equation 4 estimates
ISNS
PGND
R SENSE
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) . R SENSE must be kept higher than
700 Ω even if the number calculated comes out less
than 700 Ω :
Figure 5. Improving Current-Sensing Accuracy
R SENSE = ? ?
?
? 100 ? ?
? I LOAD(MAX ) × R DS( ON)
150 μ A
?
?
(4)
? 2004 Fairchild Semiconductor Corporation
FAN5234 ? Rev. 2.0.0
8
www.fairchildsemi.com
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| FAN5234QSC | 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 |
| FAN5234QSC_Q | 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 |
| FAN5234QSCX | 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 |
| FAN5235 | 制造商:FAIRCHILD 制造商全称:Fairchild Semiconductor 功能描述:System Electronics Regulator for Mobile PCs |
| FAN5235_CAB3026B WAF | 制造商:Fairchild Semiconductor Corporation 功能描述: |
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