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參數資料
| 型號： | SC251MLTRT |
| 廠商： | Semtech Corporation |
| 元件分類： | DC/DC變換器 |
| 英文描述： | Step-down DC-DC Converter with Bias LDO for WCDMA Amplifi ers |
| 中文描述： | 降壓型DC - DC轉換器偏置對WCDMA擴增LDO的再培訓計劃 |
| 文件頁數： | 1/19頁 |
| 文件大小： | 532K |
| 代理商： | SC251MLTRT |
1
SC251
Step-down DC-DC Converter with
Bias LDO for WCDMA Ampli
fi
ers
POWER MANAGEMENT
Description
The SC251 is a synchronous step-down converter designed
for use as an adaptive voltage supply for WCDMA RF
power ampli
fi
ers (PAs). An analog control input is used to
adjust the output voltage dynamically between 0.5V and
3.4V using a non-linear transfer function. The non-linear
relationship maximizes total system ef
fi
ciency by providing
the PA with the minimum voltage it needs to maintain
linearity. For output voltages greater than 3.4V the input
is connected directly to the output via an internal PMOS
switch. An optional gate drive (GD) output to control an
external low on-resistance PMOS switch is also provided
for systems applications that require minimal voltage
drop. The SC251 also provides a 2.85V LDO reference
output that can be used to supply a PA bias input.
May 8, 2006
www.semtech.com
Applications
3G mobile phones - RF PA power supply
WCDMA power ampli
fi
er modules
Wireless modems
Features
V
OUT
exponentially proportional to V
DAC
for maximum
ef
Output range and pass-through mode - 0.5V to 3.4V
Output current - 800mA
Shutdown current - < 1
μ
A
LDO PA bias supply - 2.85V, 10mA
Internal clock - 1MHz
Continuous short circuit protection on VOUT
Duty cycle mode - 100%
Internal PMOS bypass transistor
Gate drive available for external bypass transistor
Over 90% ef
fi
ciency
Low and high power modes for optimum dual-mode
PA ef
fi
ciency
Switching time (lowest to highest output) < 40
μ
s
Micro-lead frame package MLPD-10, 3mm x 3mm
Low power and high power modes are provided to match
performance with dual mode PAs. In low power mode the
output voltage follows an exponential relationship with
the VDAC input until it reaches 3.4V. When the VMODE
pin changes state, V
OUT
follows an alternate exponential
relationship.
The SC251 is capable of supplying output current up
to 800mA. Standby current is <1
μ
A when the device is
disabled. The internal clock runs at 1MHz so that small
surface mount inductors and capacitors can be used.
PA
L1
4.7
μ
H
C
IN
10
μ
F
VIN
VOUT
VREF
GND
LX
VDAC
PGND
C
REF
1
μ
F
EN
C
OUT
4.7
μ
F
V
IN
2.7 to 5V
2
8
10
7
1
4
5
6
9
RF Output
RF Input
Vcc
GND
BIAS
ENABLE
VDAC
SC251
VMODE
VMODE
GD
3
V
OUT
0.5V to V
IN
Optional
External Pass-through
MOSFET
Patent Pending
Typical Application Circuit
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