参数资料
| 型号： | FAN8301MX |
| 厂商： | Fairchild Semiconductor |
| 文件页数： | 8/12页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 2A 8SOIC |
| 标准包装： | 1 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 0.6 V ~ 14 V |
| 输入电压： | 4.75 V ~ 16 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 370kHz |
| 电流 - 输出： | 2A |
| 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： | 标准包装 |
| 供应商设备封装： | 8-SOICN |
| 产品目录页面： | 1216 (CN2011-ZH PDF) |
| 其它名称： | FAN8301MXDKR |
Functional Description
The FAN8301 is a monolithic, non-synchronous,
current-mode, step-down regulator with internal power
MOSFETs. It achieves 2A continuous output current
over a wide input supply range from 4.75V to 16V with
excellent load and line regulation. The output voltage
can be regulated as low as 0.6V. The FAN8301 uses
current-mode operation that provides fast transient
response and eases loop stabilization. The FAN8301
requires a minimum number of readily available
standard external components.
Current-Mode PWM Control Loop
FAN8301 uses current-mode PWM control scheme.
Maximum Load Current at Low V IN
The FAN8301 is able to operate with input supply
voltage as low as 4.75V, although the maximum
allowable output current is reduced as a function of duty
cycle (see Figure 15) . Additionally, at this low input
voltage; if the duty cycle is greater than 50%, slope
compensation reduces allowable output current.
Inductor Selection
A higher inductor value lowers ripple current. The
inductor value can be calculated as:
? 1 ? OUT
?
?
?
?
The peak inductor current is modulated in each
switching cycle by an internal op-amp output signal to
achieve the output voltage regulation. An internal slope
L =
V OUT
f S ? Δ I L
? V
V IN
?
?
(1)
compensation circuit is included to avoid sub-harmonic
oscillation at duty cycle greater than 50%. Current-
mode control provides cycle-by-cycle current limit
protection and superior regulation control loop response
than the traditional voltage-mode control.
In normal operation, the high-side MOSFET is turned on
at the beginning of each switching cycle, which causes
the current in the inductor to build up. The current-
control loop senses the inductor current by sensing the
where:
f s is the switching frequency;
V OUT is the output voltage;
V IN is the input supply voltage; and
Δ I L Is the inductor ripple current.
Considering worst case, the equation is changed to:
? 1 ? V OUT
?
?
?
voltage across the high-side senseFET during on time.
The output of the current-sense amplifier is summed
with the slope compensation signal and the combined
signal is compared with the error amplifier output to
L =
V OUT
f S ? Δ I L , MAX
?
? V IN , MAX
?
?
(2)
generate the PWM signal. As the inductor current
ramps up to the controlled value, the high-side
MOSFET is turned off and the inductor current reaches
zero through a freewheeling diode. In light-load
condition, the high-side switch may be kept off for
several cycles to improve efficiency.
Short-Circuit Protection
The FAN8301 protects output short circuit by switching
frequency fold-back. The oscillator frequency of
FAN8301 is reduced to about 45kHz when the output is
shorted to ground. This frequency fold-back allows the
inductor current more time to decay to prevent potential
Input Capacitor Selection
To prevent high-frequency switching current passing to
the input, the input capacitor impedance at the
switching frequency must be less than input source
impedance. High-value, small, inexpensive, lower-ESR
ceramic capacitors are recommended. 10μF ceramic
capacitors should be adequate for 2A applications.
Output Capacitor Selection
A larger output capacitor value keeps the output ripple
voltage smaller. The formula of output ripple Δ V OUT is:
Δ V OUT ? Δ I L ? ? ESR +
?
?
run-away condition. The oscillator frequency switches to
370kHz as V OUT rises gradually from 0V back to
regulated level.
?
?
1
8 ? C OUT ? f S
?
?
(3)
V OUT = 0 . 6 ? 1 +
?
R 3 ?
Slope Compensation and Inductor Peak
Current
The slope compensation provides stability in constant
frequency architecture by preventing sub-harmonic
oscillations at high duty cycles. It is accomplished
internally by adding a compensating ramp to the
inductor current signal at duty cycles in excess of 50%.
? 2008 Fairchild Semiconductor Corporation
FAN8301 ? Rev. 1.0.0
8
where C OUT is the output capacitor and ESR is the
equivalent series resistance of the output capacitor.
Output Voltage Programming
The output voltage is set by a resistor divider, according
to the following equation:
? R 2 ?
(4)
?
www.fairchildsemi.com
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