LTC1957-2EMS#TR Linear Technology, LTC1957-2EMS#TR Datasheet - Page 7

• Manufacturer Part Number: LTC1957-2EMS#TR
• Description: IC RF PWR CONTROLLR DUAL 10-MSOP
• Manufacturer: Linear Technology

Specifications of LTC1957-2EMS#TR

• Rf Type: Cellular, GSM, GPRS, PCS, Wireless Modem, TDMA
• Frequency: 850MHz ~ 2GHz
• Features: Dual Output
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Operating Supply Voltage (typ): 3.3/5V
• Operating Supply Voltage (min): 2.7V
• Operating Supply Voltage (max): 6V
• Operating Temp Range: 0C to 70C
• Operating Temperature Classification: Commercial
• Mounting: Surface Mount
• Pin Count: 10
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: LTC1957-2EMSTR

APPLICATIONS
cancellation over the normal 1/8 duty cycle associated
with the GSM protocol as well as multislot protocols. The
part must be in the autozero mode for at least 50 s for
autozero to settle to the correct value.
Filter
There is a 350kHz filter included in the PCTL path.
Protection Features
The RF power amplifier is overcurrent protected by an
internal sense amplifier. The sense amplifier measures the
voltage across an internal 0.050 resistor to determine
the RF power amplifier current. V
this supply current exceeds 2.2A, thereby regulating the
current to about 2.25A. The regulated current limit is
temperature compensated. The 0.050 resistor and the
current limit feature can be removed by connecting the PA
directly to V
The RF power amplifier control voltage pins are overvolt-
age protected. The V
or V
tion attempts to exceed this voltage.
The internal thermal shutdown circuit will disable the
LTC1957-2 if the junction temperature exceeds approxi-
mately 150 C. The part will be enabled when the tempera-
ture falls below 140 C.
SHDN
TXEN
BSEL
PCTL
V
V
PCA
PCB
PCB
SHUTDOWN
to 2.85V when the gain and PCTL input combina-
IN
.
VOLTAGE
AUTOZERO
START
U
PC
t
S
overvoltage clamp regulates V
INFORMATION
U
ENABLE
t
1
t
3
PCA
W
or V
PCB
t
2
is lowered as
VOLTAGE
START
U
LTC1957-2 Timing Diagram
NOTE 1
PCA
Modes of Operation
The LTC1957-2 supports three operating modes: shut-
down, autozero and enable.
In shutdown mode (SHDN = Low) the part is disabled and
supply currents will be reduced to <1 A. V
will be connected to ground via 100 switches.
In autozero mode (SHDN = High, TXEN = Low) V
V
in the autozero mode. The part must remain in autozero for
at least 50 s to allow for the autozero circuit to settle.
In enable mode (SHDN = High, TXEN = High) the control
loop and protection functions will be operational. When
TXEN is switched high, acquisition will begin. The control
amplifier will start to ramp the control voltage to the RF
power amplifier. The RF amplifier will then start to turn
on. The feedback signal from the directional coupler and
the output power will be detected by the LTC1957-2 at the
RF pin. The loop closes and the amplifier output tracks
the DAC voltage ramping at PCTL. The RF power output
will then follow the programmed power profile from the
DAC.
MODE
Shutdown
Autozero
Enable
PCB
1957 TD
will remain connected to ground and the part will be
t
t
t
t
NOTE 1: THE EXTERNAL DAC DRIVING THE PCTL PIN CAN BE ENABLED
S
1
2
3
: BSEL CHANGE PRIOR TO TXEN, 200ns TYPICAL
: BSEL CHANGE AFTER TXEN, 200ns TYPICAL
: START OF RAMP AFTER TXEN IS ASSERTED HIGH,
: AUTOZERO SETTLING TIME, 50 s MINIMUM
1 s MINIMUM, 10 s MAXIMUM
DURING AUTOZERO. THE AUTOZERO SYSTEM WILL CANCEL
THE DAC TRANSIENT. THE DAC MUST BE SETTLED TO AN OFFSET
SHDN
400mV BEFORE TXEN IS ASSERTED HIGH.
High
High
Low
LTC1957-1/LTC1957-2
TXEN
High
Low
Low
OPERATION
Disabled
Autozero
Power Control
PCA
and V
PCA
7
and
PCB