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参数资料
| 型号： | SC4501MSETRT |
| 厂商： | Semtech |
| 文件页数： | 9/21页 |
| 文件大小： | 0K |
| 描述： | IC REG BOOST ADJ 2A 8MSOP |
| 标准包装： | 1 |
| 类型： | 升压（升压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 可调至 32V |
| 输入电压： | 1.4 V ~ 16 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 1.5MHz |
| 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-TSSOP，8-MSOP（0.118"，3.00mm 宽）裸露焊盘 |
| 包装： | 标准包装 |
| 供应商设备封装： | 8-MSOP-EP |
| 其它名称： | SC4501MSEDKR |
SC4501
POWER MANAGEMENT
Application Information
1 ?
V OUT + V D
D =
1 ?
ratio V
Duty Cycle
The duty cycle D of a boost converter is:
V IN
V CESAT (3)
V OUT + V D
where V CESAT is the switch saturation voltage and V D is
voltage drop across the rectifying diode.
Maximum Output Current
It is worth noting that I OUTMAX is directly proportional to the
V IN
. Equation (4) over-estimates the maximum
OUT
output current at high frequencies (>1MHz) since
switching losses are neglected in its derivation.
Nevertheless it is a useful first-order approximation.
Using V CESAT = 0.3V, V D = 0.5V and I LIM = 2A in (3) and (4),
the maximum output currents for three V IN and V OUT
combinations are shown in Table 1.
V IN ( V )
V OUT ( V )
D
I OUTMAX ( A )
In a boost switching regulator the inductor is connected
to the input. The DC inductor current is the input current.
When the power switch is turned on, the inductor current
2.5
3.3
12
5
0.820
0.423
0.35
1.14
flows into the switch. When the power switch is off, the
inductor current flows through the rectifying diode to the
5
12
0.615
0.76
output. The output current is the average diode current.
The diode current waveform is trapezoidal with pulse width
(1 – D)T (Figure 5). The output current available from a
boost converter therefore depends on the converter
operating duty cycle. The power switch current in the
SC4501 is internally limited to 2A. This is also the maximum
inductor or the input current. By estimating the conduction
losses in both the switch and the diode, an expression of
the maximum available output current of a boost converter
can be derived:
Table 1. Calculated Maximum Output Current [ Equation (4)]
Considerations for High Frequency Operation
The operating duty cycle of a boost converter decreases as
V IN approaches V OUT . The PWM modulating ramp in a
current-mode switching regulator is the sensed current ramp
of the control switch. This current ramp is absent unless
the switch is turned on. The intersection of this ramp with
I LIM V IN ? D V D ? D ( V D ? V CESAT ) ?
? 1 ? 45 ?
I OUTMAX = ?
V OUT ? V IN ?
where I LIM is the switch current limit.
Inductor Current
IIN
(4)
the output of the voltage feedback error amplifier
determines the switch pulse width. The propagation delay
time required to immediately turn off the switch after it
is turned on is the minimum switch on time. Regulator
closed-loop measurement shows that the SC4501 has
a minimum on time of about 150ns at room temperature.
The power switch in the SC4501 is either not turned on
at all or for at least 150ns. If the required switch on time
is shorter than the minimum on time, the regulator will
ON
OFF
ON
Switch Current
either skip cycles or it will start to jitter.
Diode Current
Example: Determine the maximum operating frequency
of a Li-ion cell to 5V converter using the SC4501.
DT
(1-D)T
Assuming that V D =0.5V, V CESAT =0.3V and V IN =2.6 - 4.2V,
the minimum duty ratio can be found using (3).
5 + 0 . 5 = 0 . 25
IOUT
ON OFF ON OFF ON
Figure 5. Current Waveforms in a Boost Regulator
2011
? 2005 Semtech Corp.
9
D MIN
=
1 ?
1 ?
4 . 2
0 . 3
5 + 0 . 5
www.semtech.com
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