LTC1957-1/LTC1957-2
Single/Dual Band RF Power
Controllers with 40dB Dynamic Range
FEATURES
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DESCRIPTIO
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Dual Band RF Power Amplifier Control (LTC1957-2)
Internal Schottky Diode Detector with Improved
Dynamic Range vs the LTC1757A
Wide Input Frequency Range: 850MHz to 2GHz
Autozero Loop Cancels Offset Errors and
Temperature Dependent Offsets
Wide V
IN
Range: 2.7V to 6V
Allows Direct Connection to Battery
RF Output Power Set by External DAC
Fast Acquire After Transmit Enable
Internal Frequency Compensation
Rail-to-Rail Power Control Outputs
Power Control Signal Overvoltage Protection
Low Operating Current: 1mA
Very Low Shutdown Current: < 1µA
Available in a 8-Pin MSOP Package (LTC1957-1)
and 10-Pin MSOP (LTC1957-2)
Pin Compatible with the LTC1757A-X
Improved Start Voltage Accuracy and Range
Improved PCTL Input Filtering
The LTC
®
1957-2 is a dual band RF power controller for
power amplifiers operating in the 850MHz to 2GHz range.
The input voltage range is optimized for operation from
a single lithium-ion cell or 3× NiMH. Several functions
required for RF power control and protection are inte-
grated in one small 10-pin MSOP package, thereby
minimizing PCB area.
The LTC1957-1 is a single output RF power controller
that is identical in performance to the LTC1957-2 except
that one output (V
PCA
) is provided. The LTC1957-1 can
be used to drive a single RF or dual channel module with
integral multiplexer. This part is available in an 8-pin
MSOP package.
RF power is controlled by driving the RF amplifier power
control pins and sensing the resultant RF output power
via a directional coupler. The RF sense voltage is peak
detected using an on-chip Schottky diode. This detected
voltage is compared to the DAC voltage at the PCTL pin
to control the output power. The RF power amplifier is
protected against high supply current and high power
control pin voltages.
Internal and external offsets are cancelled over tempera-
ture by an autozero control loop, allowing accurate low
power programming. The shutdown feature disables the
part and reduces the supply current to < 1µA.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
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Single and Dual Band GSM/GPRS Cellular Telephones
PCS Devices
Wireless Data Modems
U.S. TDMA Cellular Phones
TYPICAL APPLICATIO
68Ω
V
IN
33pF
Li-Ion
SHDN
BSEL
LTC1957-2 Dual Band Cellular Telephone Transmitter
LTC1957-2
1
2
3
4
5
V
IN
RF
SHDN
BSEL
GND
V
CC
V
PCA
V
PCB
TXEN
PCTL
10
9
8
7
6
900MHz
TXEN
RF PA
DIRECTIONAL
COUPLER
DIPLEXER
DAC
1.8GHz /1.9GHz
RF PA
U
50Ω
1957 TA01
U
U
1
LTC1957-1/LTC1957-2
ABSOLUTE
AXI U
RATI GS
V
IN
to GND ............................................... – 0.3V to 6.5V
V
PCA
, V
PCB
Voltage ..................................... – 0.3V to 3V
PCTL Voltage ............................... – 0.3V to (V
IN
+ 0.3V)
RF Voltage ........................................ (V
IN
– 2.2V) to 7V
I
VCC
, Continuous ....................................................... 1A
I
VCC
, 12.5% Duty Cycle .......................................... 2.5A
SHDN, TXEN, BSEL
Voltage to GND ............................ – 0.3V to (V
IN
+ 0.3V)
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
IN
RF
SHDN
GND
1
2
3
4
8
7
6
5
V
CC
V
PCA
TXEN
PCTL
ORDER PART
NUMBER
LTC1957-1EMS8
MS8 PART MARKING
LTRH
V
IN
RF
SHDN
BSEL
GND
1
2
3
4
5
MS8 PACKAGE
8-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 160°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER
V
IN
Operating Voltage
I
VIN
Shutdown Current
I
VIN
Autozero Current
I
VIN
Operating Current
I
VCC
Current Limit
V
IN
to V
CC
Resistance
V
PCA/B
V
OL
V
PCA/B
Dropout Voltage
V
PCA/B
Voltage Clamp
V
PCA/B
Output Current
V
PCA/B
Enable Time
V
PCA/B
Bandwidth
V
PCA/B
Load Capacitance
V
PCA/B
Slew Rate
V
PCA/B
Droop
V
PCA/B
TXEN Start Voltage
SHDN = LO, TXEN = LO
CONDITIONS
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.6V, SHDN = TXEN = HI, unless otherwise noted.
MIN
q
SHDN = LO, TXEN = LO, BSEL = LO
SHDN = HI, TXEN = LO
SHDN = HI, TXEN = HI, I
VPCA
= I
VPCB
= 0mA, V
PCA/B
= HI
TXEN = HI, Open Loop, PCTL = –100mV
I
LOAD
= 5.5mA, V
IN
= 2.7V
R
LOAD
= 400Ω, PCTL = 2V, External Gain = 0.417
V
PCA/B
= 2.4V, V
IN
= 2.7V
V
PCA/B
= 2.6V, V
IN
= 3V
V
PCTL
= 2V Step, C
LOAD
= 100pF (Note 5)
C
LOAD
= 100pF, R
LOAD
= 400Ω (Note 8)
(Note 6)
V
PCTL
= 2V Step, C
LOAD
= 100pF (Note 3)
V
IN
= 2.7V, V
PCTL
= 2V Step
Open Loop, TXEN Low to High, C
LOAD
= 100pF (Note 9)
2
U
U
W
W W
U
W
(Note 1)
I
VPCA/B
, 25% Duty Cycle ...................................... 20mA
Operating Temperature Range (Note 2) . – 30°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Maximum Junction Temperature ........................ 125°C
Lead Temperature (Soldering, 10 sec)................ 300°C
TOP VIEW
10
9
8
7
6
V
CC
V
PCA
V
PCB
TXEN
PCTL
ORDER PART
NUMBER
LTC1957-2EMS
MS10 PART MARKING
LTRJ
MS10 PACKAGE
10-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 160°C/W
TYP
MAX
6
1
UNITS
V
µA
mA
mA
A
mΩ
V
V
V
mA
mA
2.7
1
1.1
2.2
90
q
q
1.6
1.7
150
0.1
V
IN
– 0.28
3.0
q
q
q
q
q
q
q
0
2.7
5.5
6.0
280
1.2
500
2.85
9
10
440
370
2.2
±1
600
650
500
100
ns
kHz
pF
V/µs
µV/ms
q
700
mV
LTC1957-1/LTC1957-2
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.6V, SHDN = TXEN = V
IN
, unless otherwise noted.
PARAMETER
SHDN Input Threshold
TXEN, BSEL Input Threshold
SHDN, TXEN, BSEL Input Current
PCTL Input Voltage Control Range
PCTL Input Voltage Range
PCTL Input Resistance
PCTL Input Filter
Autozero Range
Autozero Settling Time (t
S
)
RF Input Frequency Range
RF Input Power Range
RF Input Impedance
BSEL Timing
V
IN
= 2.7V, R
LOAD
= 400Ω (Note 4)
t
S
, Shutdown to Enable (Autozero), V
IN
= 2.7V (Note 10)
(Note 6)
900MHz (Note 6)
1800MHz (Note 6)
Referenced to V
IN
, SHDN = LO, TXEN = LO
t
1
, Setup Time Prior to TXEN Asserted High
t
2
, Hold Time After TXEN is Asserted Low
q
q
q
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
q
q
q
q
q
q
TYP
MAX
1.4
1.4
UNITS
V
V
µA
V
V
kΩ
kHz
mV
µs
MHz
dBm
dBm
Ω
ns
ns
V
IN
= 2.7V to 6V, TXEN = LO
V
IN
= 2.7V to 6V
SHDN, TXEN or BSEL = 3.6V
V
IN
= 3V to 6V, R
LOAD
= 400Ω
V
IN
= 3V, R
LOAD
= 400Ω (Note 7)
SHDN = LO, TXEN = LO
0.35
0.35
10
0
50
90
350
25
50
2
2.4
140
400
50
850
– 26
–24
100
200
200
200
2000
16
16
350
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC1957-1 and LTC1957-2 are guaranteed to meet
performance specifications from 0°C to 70°C. Specifications over the
– 30°C to 85°C operating temperature range are assured by design,
characterization and correlation with statistical process controls.
Note 3:
Slew rate is measured open loop. The slew time at V
PCA
or V
PCB
is
measured between 1V and 2V.
Note 4:
Maximum DAC zero-scale offset voltage that can be applied to
PCTL.
Note 5:
This is the time from TXEN rising edge 50% switch point to
V
PCA/B
= 1V.
Note 6:
Guaranteed by design. This parameter is not production tested.
Note 7:
Includes maximum DAC offset voltage and maximum control
voltage.
Note 8:
Bandwidth is calculated using the 10% to 90% rise time:
BW = 0.35/rise time
Note 9:
Measured 1µs after TXEN = HI.
Note 10:
50% switch point, SHDN HI = V
IN
, TXEN HI = V
IN
.
3
LTC1957-1/LTC1957-2
TYPICAL PERFOR A CE CHARACTERISTICS
PCTL REFERENCED DETECTOR OUTPUT VOLTAGE (mV)
PCTL REFERENCED DETECTOR OUTPUT VOLTAGE (mV)
Detector Characteristics
at 900MHz
10000
V
IN
= 3V TO 4.4V
1000
100
–30°C
10
1
–26
–20
–14 –8
–2
4
RF INPUT POWER (dBm)
PI FU CTIO S
(LTC1957-2/LTC1957-1)
V
IN
(Pin 1):
Input Supply Voltage, 2.7V to 6V. V
IN
should
be bypassed with 0.1µF and 100pF ceramic capacitors.
Used as return for RF 200Ω termination.
RF (Pin 2):
RF Feedback Voltage from the Directional
Coupler. Referenced to V
IN
. A coupling capacitor of 33pF
must be used to connect to the ground referenced direc-
tional coupler. The frequency range is 850MHz to 2000MHz.
This pin has an internal 200Ω termination, an internal
Schottky diode detector and peak detector capacitor.
SHDN (Pin 3):
Shutdown Input. A logic low on the SHDN
pin places the part in shutdown mode. A logic high places
the part in autozero when TXEN is low. SHDN has an inter-
nal 150k pull-down resistor to ensure that the part is in shut-
down when the drivers are in a three-state condition.
BSEL (Pin 4): (LTC1957-2 Only)
Selects V
PCA
when low
and V
PCB
when high. This input has an internal 150k
resistor to ground.
GND (Pin 5/Pin 4):
System Ground.
PCTL (Pin 6/Pin 5):
Analog Input. The external power
control DAC drives this input. The amplifier servos the RF
4
U W
75°C
25°C
Detector Characteristics
at 1800MHz
10000
V
IN
= 3V TO 4.4V
1000
100
–30°C
10
75°C
1
–24 –20 –16 –12 –8 –4 0 4 8
RF INPUT POWER (dBm)
25°C
10
16
12 16
1957 G02
1957 G01
U
U
U
power until the RF detected signal equals the DAC signal.
The input impedance is typically 90kΩ.
TXEN (Pin 7/Pin 6):
Transmit Enable Input. A logic high
enables the control amplifier. When TXEN is low and
SHDN is high the part is in the autozero mode. This input
has an internal 150k resistor to ground.
V
PCB
(Pin 8): (LTC1957-2 Only)
Power Control Voltage
Output. This pin drives an external RF power amplifier
power control pin. The maximum load capacitance is
100pF. The output is capable of rail-to-rail swings at low
load currents. Selected when BSEL is high.
V
PCA
(Pin 9/Pin 7):
Power Control Voltage Output. This pin
drives an external RF power amplifier power control pin.
The maximum load capacitance is 100pF. The output is
capable of rail-to-rail swings at low load currents. Selected
when BSEL is low (LTC1957-2 only).
V
CC
(Pin 10/Pin 8):
RF Power Amplifier Supply. This pin
has an internal 0.050Ω sense resistor between V
IN
and
V
CC
that senses the RF power amplifier supply current to
detect overcurrent conditions.
LTC1957-1/LTC1957-2
BLOCK DIAGRA
10
V
CC
0.02Ω
R
SENSE
0.05Ω
METAL
68Ω
–
CS
33pF
+
OFFSET
TRIM
V
IN
PROGRAMMABLE
200Ω
33k
35k
28pF
35k
60µA
5
GND
COMPRESSION
BG1
THERMAL
SHUTDOWN
22k
22k
TSDB
TSDB
TXENI
150k
MUX
CONTROL
PA
60µA
33k
BG1
1.2V BANDGAP
1.2V
ADJUSTABLE
12Ω
PB
100Ω
12Ω
100Ω
ICL
C
C
400µA
140k
VPC
RFDET
g
m
22k
1.2V
110k
GAIN
TRIM
g
m
50mV
FILTER
2
RF
200Ω
OPERATE SHDN
150k
W
3
(LTC1957-2)
DIPLEXER
900MHz
RF PA
50Ω
RF PA
1.8GHz/1.9GHz
Li-Ion
1
V
IN
0.02Ω
TXENB
100Ω
METAL
AUTOZERO
–
AZ
PA
V
PCA
ADJUSTABLE
9
OVERCURRENT
+
+
CAMP
PB
V
PCB
8
–+
–
+
–
XMT AUTOZERO
150k
SHDN
7
TXEN
6
PCTL
4
BSEL
1957 BD
5
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