SC250 Datasheet, PDF (1/18 Pages) Motorola, Inc – TRIACS BIDIRECTIPNAL TRIODE THYRISTORS

SC250
Step-Down DC-DC Converter with
Bias LDO for RF Power Amplifiers
POWER MANAGEMENT
Description
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.
Features
‹ Adjustable output voltage range — 0.3 to 3.6V
‹ Linearly proportional V_DAC to V_OUT 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
Applications
‹ CDMA and WCDMA Phones
‹ Handheld Radios
‹ RF PC Cards
‹ Battery Powered RF Devices
Typical Application Circuit
V_IN
C_IN
10μF
ENABLE
VDAC
2
VIN
7
EN
SC250
5
VDAC
8
PGND
1
LX
6
VOUT
VREF ³
4
GND
L1
4.7μH
C_REF
1μF
C_OUT
4.7μF
Vcc
RF Input
PA
BIAS GND
RF Output
August 28, 2006
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