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SC250 Datasheet(PDF) 1 Page - Semtech Corporation

Part No. SC250
Description  Step-Down DC-DC Converter with Bias LDO for RF Power Amplifi ers
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Maker  SEMTECH [Semtech Corporation]
Homepage  http://www.semtech.com
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SC250 Datasheet(HTML) 1 Page - Semtech Corporation

 
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SC250
Step-Down DC-DC Converter with
Bias LDO for RF Power Amplifiers
POWER MANAGEMENT
August 28, 2006
Typical Application Circuit
Applications
The SC250 is a synchronous step-down converter
designed specifically for use as an adaptive voltage
supply for CDMA and WCDMA RF Power Amplifiers (PAs).
The output voltage can be adjusted dynamically between
0.3V and (Vin - 0.4)V through a linear analog control input.
For high power operation, a maximum control input signal
level forces the device into bypass mode where the input
is connected directly to the output via an internal P-
Channel pass transistor. Bypass mode also occurs when
the output load demands duty cycles in excess of the
maximum rated duty cycle.
The SC250 also provides an LDO regulator which can be
used to supply a 2.85V bias to the PA. The internal clock
runs at 1MHz to maximize efficiency while still allowing
the use of small surface mount inductors and capacitors
can be used.
The peak current rating of the internal PMOS switch allows
a DC output current of 600mA. The bypass PMOS current
rating allows a minimum of 1A DC output current in the
bypass mode. Shutdown turns off all the control circuitry
to achieve a typical shutdown current of 0.1μA.
CDMA and WCDMA Phones
Handheld Radios
RF PC Cards
Battery Powered RF Devices
Adjustable output voltage range — 0.3 to 3.6V
Linearly proportional V
DAC to VOUT relationship for
increased PA efficiency
Pass-through mode automatic and on demand
Input voltage range — 2.7V to 5V
Typical settling time — 40μs
Output current capability — 600mA
Maximum output current in bypass mode — 1A
Up to 96% efficiency
Constant frequency operation — 1MHz
Less than 1μA shutdown current
Internal 75mΩ PMOS bypass transistor
PA bias voltage supply — 2.85V, 20mA, 1.5%
MLPD-W8, 2.3 x 2.3mm package
L1
4.7μH
CIN
10μF
VIN
VOUT
VREF
GND
LX
VDAC
PGND
CREF
1μF
EN
COUT
4.7μF
VIN
3
6
1
4
2
7
5
8
PA
RF Output
RF Input
Vcc
GND
BIAS
ENABLE
VDAC
SC250
Description
Features


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