LTC1757A-2

LTC1757A-1/LTC1757A-2 Single/Dual Band RF Power Controllers FEATURES s s s s DESCRIPTIO s s s s s s s s s s s Dual Band RF Power Amplifier Control (LTC1757A-2) Improved Internal Schottky Diode Detector Wide Input Frequency Range: 850MHz to 2GHz Autozero Cancels Initial Offsets and Temperature Dependent Offset Errors Wide VIN Range of 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 RF PA Supply Current Limiting Battery Overvoltage Protection Power Control Signal Overvoltage Protection Low Operating Current: 1mA Very Low Shutdown Current: < 1µA Available in a 8-Pin MSOP Package (LTC1757A-1) and 10-Pin MSOP (LTC1757A-2) The LTC®1757A-2 is a dual band RF power controller for RF power amplifiers operating in the 850MHz to 2GHz range. The LTC1757A is pin compatible with the LTC1757 but has improved RF detection 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 integrated in one small 10-pin MSOP package, thereby minimizing PCB area. The LTC1757A-1 is a single output RF power controller that is identical in performance to the LTC1757A-2 except that one output (VPCA) is provided. The LTC1757A-1 can be used to drive a single RF channel 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 voltage and current and high power control pin voltages. Internal and external offsets are cancelled over temperature by an autozero control loop, allowing accurate low power programming. The shutdown feature disables the part and reduces the supply current to < 1µA. APPLICATIO S s s s s Single/Dual Band GSM Cellular Telephones PCS Devices Wireless Data Modems TDMA Cellular Telephones , LTC and LT are registered trademarks of Linear Technology Corporation. TYPICAL APPLICATIO 68Ω VIN 33pF Li-Ion SHDN BSEL LTC1757A-2 Dual Band Cellular Telephone Transmitter LTC1757A-2 1 2 3 4 5 VIN RF SHDN BSEL GND VCC VPCA VPCB TXEN PCTL 10 9 8 7 6 900MHz TXEN RF PA DIRECTIONAL COUPLER DIPLEXER DAC 1.8GHz /1.9GHz RF PA U 50Ω 1757A TA01 U U 1 LTC1757A-1/LTC1757A-2 ABSOLUTE AXI U RATI GS VIN to GND ............................................... – 0.3V to 6.5V VPCA, VPCB Voltage ..................................... – 0.3V to 3V PCTL Voltage ............................... – 0.3V to (VIN + 0.3V) RF Voltage ........................................ (VIN – 2.2V) to 7V IVCC, Continuous ....................................................... 1A IVCC, 12.5% Duty Cycle .......................................... 2.5A SHDN, TXEN, BSEL Voltage to GND ............................ – 0.3V to (VIN + 0.3V) PACKAGE/ORDER I FOR ATIO TOP VIEW VIN RF SHDN GND 1 2 3 4 8 7 6 5 VCC VPCA TXEN PCTL ORDER PART NUMBER LTC1757A-1EMS8 MS8 PART MARKING LTPL VIN RF SHDN BSEL GND 1 2 3 4 5 MS8 PACKAGE 8-LEAD PLASTIC MSOP TJMAX = 150°C, θJA = 250°C/W Consult factory for Industrial and Military grade parts. ELECTRICAL CHARACTERISTICS PARAMETER VIN Operating Voltage IVIN Shutdown Current IVIN Autozero Current IVIN Operating Current IVCC Current Limit VIN to VCC Resistance VPCA/B VOL VPCA/B Dropout Voltage VPCA/B Voltage Clamp VPCA/B Output Current VPCA/B Enable Time VPCA/B Bandwidth VPCA/B Load Capacitance VPCA/B Slew Rate VPCA/B Droop VPCA/B TXEN Start Voltage SHDN Input Threshold TXEN, BSEL Input Threshold SHDN = LO, TXEN = LO CONDITIONS (Note 7) The q denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, SHDN = TXEN = HI, unless otherwise noted. MIN q q q q SHDN = LO, TXEN = LO, BSEL = LO SHDN = HI, TXEN = LO SHDN = HI, TXEN = HI, IVPCA = IVPCB = 0mA, VPCA/B = HI TXEN = HI, Open Loop, PCTL = – 100mV ILOAD = 5.5mA, VIN = 2.7V RLOAD = 400Ω VPCA/B = 2.4V, VIN = 2.7V VPCTL = 2V Step, CLOAD = 100pF (Note 5) CLOAD = 100pF, RLOAD = 400Ω (Note 9) (Note 6) VPCTL = 2V Step, CLOAD = 100pF (Note 3) VIN = 2.7V, VPCTL = 2V Step Open Loop, TXEN Low to High, CLOAD = 100pF (Note 10) VIN = 2.7V to 6V, TXEN = LO VIN = 2.7V to 4.7V 2 U U W WW U W (Note 1) IVPCA/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 VCC VPCA VPCB TXEN PCTL ORDER PART NUMBER LTC1757A-2EMS MS10 PART MARKING LTPM MS10 PACKAGE 10-LEAD PLASTIC MSOP TJMAX = 125°C, θJA = 250°C/W TYP MAX 6 1 UNITS V µA mA mA A mΩ V V V mA ns 2.7 0.9 1 2.2 90 1.5 1.6 150 0.1 VIN – 0.28 3.0 q q q q 0 2.7 5.5 250 1.5 400 2.85 9 200 400 3 ± 10 550 q 550 100 kHz pF V/µs µV/ms 700 1.4 1.4 mV V V q q 0.35 0.35 LTC1757A-1/LTC1757A-2 ELECTRICAL CHARACTERISTICS PARAMETER 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 (tS) RF Input Frequency Range RF Input Power Range RF DC Input Resistance VIN Overvoltage Range BSEL Timing CONDITIONS The q denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, SHDN = TXEN = HI, unless otherwise noted. MIN q q q q TYP 30 MAX 50 2 2.4 UNITS µA V V kΩ MHz mV µs MHz dBm dBm Ω V ns ns SHDN, TXEN or BSEL = 3.6V VIN = 2.7V to 4.7V, RLOAD = 400Ω VIN = 3V, RLOAD = 400Ω (Note 8) SHDN = LO, TXEN = LO VIN = 2.7V, RLOAD = 400Ω (Note 4) Shutdown to Enable (Autozero), VIN = 2.7V (Note 11) (Note 6) 900MHz (Note 6) 1800MHz (Note 6) Referenced to VIN, SHDN = LO, TXEN = LO VPCA/B < 0.5V, RLOAD = 400Ω t1, Setup Time Prior to TXEN Asserted High t2, Hold Time After TXEN is Asserted Low 10 0 50 100 1.25 150 400 50 q q q 850 – 24 –22 2000 16 16 185 5.0 200 200 300 5.4 q q 100 4.8 Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LTC1757A-1 and LTC1757A-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 VPCA or VPCB 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 VPCA/B = 1V. Note 6: Guaranteed by design. This parameter is not production tested. Note 7: For VIN voltages greater than 4.7V, VPCA/VPCB are set low by the overvoltage shutdown. Note 8: Includes maximum DAC offset voltage and maximum control voltage. Note 9: Bandwidth is calculated using the 10% to 90% rise time equation: BW = 0.35/rise time Note 10: Measured 1µs after TXEN = HI. Note 11: 50% switch point, SHDN HI = VIN, TXEN HI = VIN. 3 LTC1757A-1/LTC1757A-2 TYPICAL PERFOR A CE CHARACTERISTICS PCTL REFERENCED DETECTOR OUTPUT VOLTAGE (mV) 10000 PCTL REFERENCED DETECTOR OUTPUT VOLTAGE (mV) RF Detector Characteristics at 900MHz VIN = 3V TO 4.4V 1000 100 10 –30°C 25°C 1 –24 –20 –16 –12 –8 –4 0 4 8 RF INPUT POWER (dBm) 12 16 1757A G01 PI FU CTIO S (LTC1757A-2/LTC1757A-1) VIN (Pin 1): Input Supply Voltage, 2.7V to 6V. VIN should be bypassed with 0.1µF and 100pF ceramic capacitors. Used as return for RF 185Ω termination. RF (Pin 2): RF Feedback Voltage from the Directional Coupler. Referenced to VIN. A coupling capacitor of 33pF must be used to connect to the ground referenced directional coupler. The frequency range is 850MHz to 2000MHz. This pin has an internal 185Ω 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 internal 150k pull-down resistor to ensure that the part is in shutdown when the drivers are in a three-state condition. BSEL (Pin 4): (LTC1757A-2 Only) Selects VPCA when low and VPCB 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 power until the RF detected signal equals the DAC signal. The input resistance is typically 100k. 4 UW 75°C RF Detector Characteristics at 1800MHz 10000 VIN = 3V TO 4.4V 1000 100 10 –30°C 75°C 25°C 1 –22 –18 –14 –10 –6 –2 2 6 RF INPUT POWER (dBm) 10 14 1757A G02 U U U 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. VPCB (Pin 8): (LTC1757A-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. VPCA (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 (LTC1757A-2 only). VCC (Pin 10/Pin 8): RF Power Amplifier Supply. This pin has an internal 0.050Ω sense resistor between VIN and VCC that senses the RF power amplifier supply current to detect overcurrent conditions. LTC1757A-1/LTC1757A-2 BLOCK DIAGRA 10 VCC 0.02Ω RSENSE 0.05Ω METAL 68Ω – CS 33pF + OFFSET TRIM 185Ω VIN 600mV GAIN TRIM gm 50mV 2 RF 22pF 42k 60µA 5 GND 60µA BG1 THERMAL SHUTDOWN OPERATE SHDN 150k W 42k 3 (LTC1757A-2) DIPLEXER 900MHz RF PA 50Ω RF PA 1.8GHz Li-Ion 1 VIN 0.02Ω 100Ω METAL TXENB AUTOZERO – AZ PA VPCA 9 OVERCURRENT + + – + CAMP PB ADJ –+ 6pF ICL – CC 400µA 140k VPCB 8 + RFDET 33k VPC gm 110k – 16.7k 33k 1.2V OVP gm BG1 1.2V BANDGAP 1.2V 600mV 33k 54.5k 12Ω TSDB TSDB TXENI 150k MUX CONTROL PA PB 100Ω 12Ω 100Ω 173k VIN XMT AUTOZERO 150k SHDN 7 TXEN 6 PCTL 4 BSEL 1757A BD 5 LTC1757A-1/LTC1757A-2 APPLICATIO S I FOR ATIO Operation The LTC1757A-2 dual band RF power control amplifier integrates several functions to provide RF power control over two frequencies ranging from 850MHz to 2GHz. The device also prevents damage to the RF power amplifier due to overvoltage or overcurrent conditions. These functions include an internally compensated power control amplifier to control the RF output power, an autozero section to cancel internal and external voltage offsets, a sense amplifier with an internal sense resistor to limit the maximum RF power amplifier current, an RF Schottky diode peak detector and amplifier to convert the RF feedback signal to DC, a VPCA/B overvoltage clamp, a VIN overvoltage detector, a bandgap reference, a thermal shutdown circuit and a multiplexer to switch the control amplifier output to either VPCA or VPCB. Band Selection The LTC1757A-2 is designed for dual band operation. The BSEL pin will select output VPCA when low and output VPCB when high. For example, VPCA could be used to drive a 900MHz channel and VPCB a 1.8GHz/1.9GHz channel. BSEL must be established before the part is enabled. The LTC1757A-1 can be used to drive a single RF channel or dual channel module with integral multiplexer. Control Amplifier The control amplifier supplies the power control voltage to the RF power amplifier. A portion (typically – 19dB for low frequencies and –14dB for high frequencies) of the RF output signal is sampled, via a directional coupler, to close the gain control loop. When a DAC signal is applied to PCTL, the amplifier quickly servos VPCA or VPCB positive until the detected feedback voltage applied to the RF pin matches the voltage at PCTL. This feedback loop provides accurate RF power control. VPCA or VPCB are capable of driving a 5.5mA load current and 100pF load capacitor. RF Detector The internal RF Schottky diode peak detector and amplifier converts the RF feedback voltage from the directional coupler to a low frequency voltage. This voltage is compared to the DAC voltage at the PCTL pin by the control 6 U amplifier to close the RF power control loop. The RF pin input resistance is typically 185Ω and the frequency range of this pin is 850MHz to 2000MHz. The detector demonstrates excellent efficiency and linearity over a wide range of input power. The Schottky detector is biased at about 60µA and drives an on-chip peak detector capacitor of 22pF. Autozero An autozero system is included to improve power programming accuracy over temperature. This section cancels internal offsets associated with the Schottky diode detector and control amplifier. External offsets associated with the DAC driving the PCTL pin are also cancelled. Offset drift due to temperature is cancelled between each burst by the autozero system. The maximum offset allowed at the DAC output is limited to 400mV. Autozeroing is performed when the part is in autozero mode (SHDN = high, TXEN = low). When the part is enabled (TXEN = high, SHDN = high) the autozero capacitors are held and the VPCA or VPCB pin is connected to the control amplifier output. The hold droop voltage of typically 10µV/ms provides for accurate offset cancellation over the 1/8 duty cycle associated with the GSM protocol as well as multislot protocals. The part must be in the autozero mode for at least 50µs for autozero to settle to the correct value. Protection Features The RF power amplifier is overcurrent protected by an internal sense amplifier. The sense amplifier measures the voltage across an internal 0.050Ω resistor to determine the RF power amplifier current. VPCA or VPCB is lowered as this supply current exceeds 2.2A, thereby regulating the current to about 2.25A. The regulated current limit is temperature compensated. The 0.050Ω resistor and the current limit feature can be removed by connecting the PA directly to VIN. The RF power amplifier control voltage pins are overvoltage protected. The VPC overvoltage clamp regulates VPCA or VPCB to 2.85V when the gain and PCTL input combination attempts to exceed this voltage. The RF power amplifier is protected against excessive input supply voltages. The VIN overvoltage detector starts W UU LTC1757A-1/LTC1757A-2 APPLICATIO S I FOR ATIO to reduce VPCA or VPCB when VIN exceeds 5V. VPCA or VPCB will be reduced to 0V as VIN continues to increase by about 200mV. This gain control voltage reduction lowers the RF output power eventually reducing it to zero. The internal thermal shutdown circuit will disable the LTC1757A-2 if the junction temperature exceeds approximately 150°C. The part will be enabled when the temperature falls below 140°C. Modes of Operation The LTC1757A-2 supports three operating modes: shutdown, autozero and enable. In shutdown mode (SHDN = Low) the part is disabled and supply currents will be reduced to