LTC1758-2EMS#TR Linear Technology, LTC1758-2EMS#TR Datasheet - Page 7

• Manufacturer Part Number: LTC1758-2EMS#TR
• Description: IC RF PWR CONTROLLR DUAL 10-MSOP
• Manufacturer: Linear Technology

Specifications of LTC1758-2EMS#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
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: LTC1758-2EMSTR

APPLICATIONS
Filter
There is a 350kHz single pole 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 0.090 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 0.090 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
LTC1758-2 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
PCA
W
or V
PCB
t
2
is lowered as
VOLTAGE
START
U
LTC1758-2 Timing Diagram
NOTE 1
PCA
Modes of Operation
The LTC1758-2 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 LTC1758-2 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
1758 TD
will remain connected to ground and the part will be
t
t
t
NOTE 1: THE EXTERNAL DAC DRIVING THE PCTL PIN CAN BE ENABLED
S
1
2
: BSEL CHANGE PRIOR TO TXEN, 200ns TYPICAL
: BSEL CHANGE AFTER TXEN, 200ns TYPICAL
: AUTOZERO SETTLING TIME, 50 s MINIMUM
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
LTC1758-1/LTC1758-2
TXEN
High
Low
Low
OPERATION
Disabled
Autozero
Power Control
PCA
and V
PCA
7
and
PCB