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| 型号： | FAN4860UMP5X |
| 厂商： | Fairchild Semiconductor |
| 文件页数： | 13/19页 |
| 文件大小： | 0K |
| 描述： | IC REG BOOST SYNC 5V 0.2A 6UMLP |
| 标准包装： | 1 |
| 系列： | TinyBoost™ |
| 类型： | 升压（升压） |
| 输出类型： | 固定 |
| 输出数： | 1 |
| 输出电压： | 5V |
| 输入电压： | 2.3 V ~ 4.5 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 3MHz |
| 电流 - 输出： | 200mA |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 6-UDFN 裸露焊盘 |
| 包装： | 标准包装 |
| 供应商设备封装： | 6-UMLP（2x2） |
| 其它名称： | FAN4860UMP5XDKR |
Functional Description
Circuit Description
The FAN4860 is a synchronous boost regulator, typically
operating at 3 MHz in Continuous Conduction Mode
(CCM), which occurs at moderate to heavy load current
and low V IN voltages.
At light-load currents, the converter switches automatically to
power-saving PFM Mode. The regulator automatically and
smoothly transitions between quasi-fixed-frequency
PFM Mode
If V OUT > V REF when the minimum off-time has ended, the
regulator enters PFM Mode. Boost pulses are inhibited until
V OUT < V REF . The minimum on-time is increased to enable
the output to pump up sufficiently with each PFM boost
pulse. Therefore, the regulator behaves like a constant on-
time regulator, with the bottom of its output voltage ripple at
5.05 V in PFM Mode.
continuous conduction PWM Mode and variable-frequency
PFM Mode to maintain the highest possible efficiency over
the full range of load current and input voltage.
Table 1.
Mode
Operating States
Description
Invoked When:
PWM Mode Regulation
The FAN4860 uses a minimum on-time and computed
minimum off-time to regulate V OUT . The regulator achieves
excellent transient response by employing current mode
modulation. This technique causes the regulator output to
exhibit a load line. During PWM Mode, the output voltage
drops slightly as the input current rises. With a constant V IN ,
this appears as a constant output resistance.
The “droop” caused by the output resistance when a load is
applied allows the regulator to respond smoothly to load
LIN Linear Startup V IN > V OUT
SS Boost Soft-Start V OUT < V REG
BST Boost Operating Mode V OUT =V REG
Shutdown and Startup
If EN is LOW, all bias circuits are off and the regulator is in
Shutdown Mode. During shutdown, true load disconnect
between battery and load prevents current flow from V IN to
V OUT , as well as reverse flow from V OUT to V IN .
LIN State
transients with negligible overshoot.
700
600
500
400
300
200
3.3 Vout
5.0 Vout
When EN rises, if V IN > UVLO, the regulator first attempts to
bring V OUT within about 1V of V IN by using the internal fixed
current source from V IN (I LIN1 ). The current is limited to about
630 mA during LIN1 Mode.
If V OUT reaches V IN -1V during LIN1 Mode, the SS state is
initiated. Otherwise, LIN1 times out after 16 clock counts and
the LIN2 Mode is entered.
In LIN2 Mode, the current source is incremented to 850 mA.
If V OUT fails to reach V IN -1 V after 64 clock counts, a fault
condition is declared.
SS State
Upon the successful completion of the LIN state (V OUT >V IN -
1 V), the regulator begins switching with boost pulses current
100
2.0
2.5
3.0
3.5
Input Voltage (V)
4.0
4.5
5.0
limited to about 50% of nominal level, incrementing to full
scale over a period of 32 clock counts.
Figure 46. Output Resistance ( ROUT )
When the regulator is in PWM CCM Mode and the target
V OUT = 5.05 V, V OUT is a function of I LOAD and can be
computed as:
If the output fails to achieve 90% of its set point within 96 clock
counts at full-scale current limit, a fault condition is declared.
BST State
This is the normal operating mode of the regulator. The
V OUT ? 5 . 05 ? R OUT ? I LOAD
(1)
regulator uses a minimum t OFF -minimum t ON modulation
V IN
For example, at V IN =3.3 V, and I LOAD =200 mA, V OUT drops to:
scheme. Minimum t OFF is proportional to V OUT , which keeps
the regulator’s switching frequency reasonably constant in
V OUT ? 5 . 05 ? 0 . 38 ? 0 . 2 ? 4 . 974 V
At V IN =2.3 V, and I LOAD =200 mA, V OUT drops to:
V OUT ? 5 . 05 ? 0 . 68 ? 0 . 2 ? 4 . 914 V
? 2010 Fairchild Semiconductor Corporation
FAN4860 ? Rev. 1.1.1
(1A)
(1B)
13
CCM. t ON(MIN) is proportional to V IN and is higher if the inductor
current reaches 0 before t OFF(MIN) during the prior cycle.
To ensure that V OUT does not pump significantly above the
regulation point, the boost switch remains off as long as
FB > V REF .
www.fairchildsemi.com
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