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| 型号： | FAN5236MTCX |
| 厂商： | Fairchild Semiconductor |
| 文件页数： | 11/19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 |
Initialization and Soft Start
Assuming EN is HIGH, FAN5236 is initialized when V CC
exceeds the rising UVLO threshold. Should V CC drop
below the UVLO threshold, an internal power-on reset
function disables the chip.
The voltage at the positive input of the error amplifier is
limited by the voltage at the SS pin, which is charged
with a 5 μ A current source. Once C SS has charged to
V REF (0.9V) the output voltage is in regulation. The time
it takes SS to reach 0.9V is:
frequency PWM Mode, as shown in Figure 11. This
mode achieves high efficiency at nominal load. When
the load current decreases to the point where the
inductor current flows through the lower MOSFET in the
‘reverse’ direction, the SW node becomes positive and
the mode is changed to hysteretic, which achieves
higher efficiency at low currents by decreasing the
effective switching frequency.
To prevent accidental mode change or "mode chatter,"
the transition from PWM to Hysteretic Mode occurs
when the SW node is positive for eight consecutive
t 0 . 9 =
0 . 9 xC SS
5
(1)
clock cycles, as shown in Figure 11. The polarity of the
SW node is sampled at the end of the lower MOSFET
conduction time. At the transition between PWM and
where t 0.9 is in seconds if C SS is in μ F.
When SS reaches 1.5V, the power-good outputs are
enabled and Hysteretic Mode is allowed. The converter
is forced into PWM Mode during soft-start.
Operation Mode Control
The mode-control circuit changes the converter mode
Hysteretic Mode, the upper and lower MOSFETs are
turned off. The phase node “rings” based on the output
inductor and the parasitic capacitance on the phase
node and settles out at the value of the output voltage.
The boundary value of inductor current, where current
becomes discontinuous, can be estimated by the
following expression:
? ( V
I LOAD ( DIS ) = ?
? 2 F SW L OUT V IN
?
?
from PWM to hysteretic and vice versa, based on the
voltage polarity of the SW node when the lower
MOSFET is conducting and just before the upper
MOSFET turns on. For continuous inductor current, the
?
)
? IN ? V OUT V OUT
?
?
?
(2)
SW node is negative when the lower MOSFET is
conducting and the converters operate in fixed-
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
Hysteretic Mode
Figure 11.
Transitioning Between PWM and Hysteretic Mode
Conversely, the transition from Hysteretic Mode to
PWM Mode occurs when the SW node is negative for
eight consecutive cycles.
A sudden increase in the output current causes a
change from Hysteretic to PWM Mode. This load
increase causes an instantaneous decrease in the
output voltage due to the voltage drop on the output
capacitor ESR. If the load causes the output voltage (as
presented at V SNS ) to drop below the hysteretic
regulation level (20mV below V REF ), the mode is
changed to PWM on the next clock cycle.
In Hysteretic Mode, the PWM comparator and the error
amplifier that provide control in PWM Mode are
inhibited and the hysteretic comparator is activated. In
Hysteretic Mode, the low-side MOSFET is operated as
a synchronous rectifier, where the voltage across
? 2002 Fairchild Semiconductor Corporation
FAN5236 ? Rev. 1.3.2
11
V DS(ON) is monitored and switched off when V DS(ON) goes
positive (current flowing back from the load), allowing
the diode to block reverse conduction.
The hysteretic comparator initiates a PFM signal to turn
on HDRV at the rising edge of the next oscillator clock,
when the output voltage (at V SNS ) falls below the lower
threshold (10mV below V REF ) and terminates the PFM
signal or when V SNS rises over the higher threshold
(5mV above V REF ). The switching frequency is primarily
a function of:
Spread between the two hysteretic thresholds
I LOAD
Output inductor and capacitor ESR.
www.fairchildsemi.com
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相关代理商/技术参数 |
参数描述 |
|---|---|
| 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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