LTC1340 Low Noise, Voltage-Boosted Varactor Driver U DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ The LTC®1340 is a varactor diode driver designed to generate 5V varactor drive from a single 3V or higher voltage supply. It includes a low noise amplifier with an internal gain of 2.3 and a self-contained charge pump to generate output voltages above the input supply. The amplifier input stage includes a built-in offset voltage that allows the output voltage to swing to ground without requiring OV on the input. This feature maintains the phase detector within its linear range of operation. The LTC1340 requires only three external surface mount capacitors to implement a complete varactor driver module. The LTC1340 features output referred noise of 15µVRMS, minimizing frequency deviation in PLL frequency synthesizer systems. Supply current is 400µA typically with a 3V supply, and drops to 1µA in shutdown, maximizing operating life in battery-powered systems. Amplifier bandwidth is useradjustable from 10kHz up to 500kHz and the output typically sinks or sources 20µA, allowing fast output signal changes with a typical varactor load. The amplifier input features railto-rail input common mode range, allowing it to interface with the output of virtually any phase detector circuit. The LTC1340 is available in MS8 and SO-8 packages. Generates 5V Varactor Drive from a 3V Supply Wide Supply Voltage Range: 2.7V to 6V Requires Only Three External Components Micropower Operation: 400µA at 3V Supply Shutdown Mode Drops Supply Current Below 1µA Low Output Noise: 15µVRMS Amplifier Gain: 2.3 Up to 500kHz Signal Bandwidth MS8 and SO-8 Packages Very Low Input Bias Current: 10nA Max Amplifier Offset Maintains Phase Detector in Linear Region U APPLICATIONS ■ ■ ■ ■ ■ ■ 5V Varactor Drive from a Single Li-Ion Cell 5V Varactor Drive from Three NiCd/NiMH Cells Cellular Telephones Portable RF Equipment Radio Modems Wireless Data Transmission , LTC and LT are registered trademarks of Linear Technology Corporation. U TYPICAL APPLICATION Spectral Plot of VCO Output Driven by LTC1340 Resolution Bandwidth = 300Hz Low Voltage Frequency Synthesizer 3V 1 2 VCC 0.1µF 8 CP 0.1µF AVCC LTC1340 PHASE DETECTOR 5 IN OUT 7 0V TO 5V AV = 2.3 LOOP FILTER VCO 270pF SHDN PGND AGND 4 3 6 SHUTDOWN RELATIVE POWER (10dB/DIV) 0dB VCC = 3V COUT = 270pF 1340 TA01 900MHz FREQUENCY (120kHz/DIV) 1340 TA02 1 LTC1340 W W U W ABSOLUTE MAXIMUM RATINGS Supply Voltage (VCC) ................................................. 7V Input Voltage (AVCC) ............................................... 14V Input Voltage (SHDN, IN) ............... – 0.3V to VCC + 0.3V Output Voltage (CP, OUT) ............ – 0.3V to AVCC + 0.3V Output Short-Circuit Duration .......................... Indefinite Commercial Temperature Range ................. 0°C to 70°C Extended Commercial Operating Temperature Range (Note 1) ............. – 40°C to 85°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec.)................. 300°C U W U PACKAGE/ORDER INFORMATION TOP VIEW CP VCC SHDN PGND 1 2 3 4 8 7 6 5 AVCC OUT AGND IN MS8 PACKAGE 8-LEAD PLASTIC MSOP ORDER PART NUMBER LTC1340CMS8 MS8 PART MARKING CP 1 8 AVCC VCC 2 7 OUT SHDN 3 6 AGND PGND 4 5 IN LTBM TJMAX = 125°C, θJA = 200°C/ W ORDER PART NUMBER TOP VIEW LTC1340CS8 S8 PART MARKING S8 PACKAGE 8-LEAD PLASTIC SO 1340 TJMAX = 125°C, θJA = 130°C/ W Consult factory for Industrial and Military grade parts. ELECTRICAL CHARACTERISTICS TA = 25°C, unless otherwise noted. (Note 1) SYMBOL PARAMETER CONDITIONS MIN VCC Input Supply Voltage ICC Supply Current IOUT = 0, 2.7V ≤ VCC ≤ 6V Shutdown, 2.7V ≤ VCC ≤ 6V ● ● VOL Low Output Voltage Swing VCC = 2.7V, 6V, IOUT = 0µA VCC = 2.7V, 6V, IOUT = 14µA ● ● VOH High Output Voltage Swing VCC = 2.7V, IOUT = 0µA VCC = 6V, IOUT = 0µA VCC = 2.7V, IOUT = 14µA VCC = 6V, IOUT = 14µA ● ● ● ● 4.6 10.5 4.25 9.75 I OUT Output Sink/Source Current 0.6V ≤ VOUT ≤ 4.25V, VCC = 2.7V 0.6V ≤ VOUT ≤ 9.75V, VCC = 6V ● ● ±14 ±14 t OUT Output Transition Time COUT = 1nF, ∆VOUT = ±4V ● VIN Input Voltage Range IB Input Bias Current ● ● TYP MAX 6 V 500 1 900 10 µA µA 0.25 0.6 V V 2.7 V V V V ±20 ±20 ±35 ±35 µA µA 200 285 µs VCC V ±0.01 ±1 ±10 nA nA 0 0.1V ≤ VIN ≤ VCC ● VOS Input Offset Voltage AV Amplifier Gain gm Amplifier Transconductance UNITS ● 0.15 0.35 0.60 V VIN = 1V, AVCC = 5V ● 2.1 2.3 2.5 V/V VOUT = 2.5V, AVCC = 5V VOUT = 2.5V, AVCC = 5V 1200 800 1800 ● 2300 3200 ROUT Output Impedance VOUT = 1/2AVCC en Output Noise Voltage 1kHz to 100kHz, COUT = 1nF 15 BW – 3dB Signal Bandwidth COUT = 1nF 125 kHz PSRR Power Supply Rejection Ratio AVCC = 4V to 6V, COUT = 1nF 90 dB ISHDN Shutdown Logic Input Current 0.1V ≤ VSHDN ≤ VCC 2 1 µmho µmho ● 60 ±0.01 MΩ 25 ±1 µVRMS µA LTC1340 ELECTRICAL CHARACTERISTICS SYMBOL PARAMETER TA = 25°C, unless otherwise noted. (Note 1) CONDITIONS MIN tSTART Charge Pump Start-Up Time CCP = 0.1µF, VCC = 2.7V, IOUT = 0 VRIPPLE Charge Pump Output Ripple at CP CCP = CVCC = 0.1µF, VCC = 2.7V, IOUT = 0 (Note 2) f CP Charge Pump Frequency (Note 3) ● ● The ● denotes specifications which apply over the specified temperature range. Note 1: C grade device specifications are guaranteed over the 0°C to 70°C temperature range. In addition, C grade device specifications are assured over the – 40°C to 85°C temperature range by design or correlation, but are not production tested. 2.5 TYP MAX 1.2 5 UNITS ms 200 µVP-P 4 MHz Note 2: The charge pump output ripple is not tested but is correlated with a PCB ground plane and high quality, low ESR, low ESL metalized polyester 0.1µF capacitors. Note 3: The internal oscillator typically runs at 2MHz, but the charge pump refreshes the output on both phases of the clock, resulting in an effective 4MHz operating frequency. U W TYPICAL PERFORMANCE CHARACTERISTICS 8 7 6 VCC = 2.7V 5 0.60 144 0.55 –10 72 –20 36 0 –30 PHASE –40 –36 –50 –72 3 –60 –108 2 –70 1 –80 4 0 1 2 3 4 INPUT VOLTAGE (V) 5 6 VCC = 2.7V TA = 25°C COUT = 1nF –144 10 100 FREQUENCY (kHz) 1 1340 G01 OUTPUT LOW VOLTAGE (V) IOH = 14µA, VCC = 5V 9.0 COUT = 1nF VIN = VSHDN = VCC 4.9 IOH = 0, VCC = 2.7V 4.8 4.7 IOH = 14µA, VCC = 2.7V 4.6 0.35 0.30 0.25 –25 25 50 75 0 TEMPERATURE (°C) 0.4 100 125 1340 G03 Transconductance vs Supply Voltage 0.5 IOH = 0, VCC = 5V 9.2 8.9 0.40 Output Low Voltage vs Temperature 9.4 9.1 0.45 1340 G02 Output High Voltage vs Temperature 9.3 0.50 0.15 –50 –216 1000 –90 VCC = 2.7V TO 6V COUT = 1nF VSHDN = VCC 0.20 –180 2100 VCC = 2.7V OR 5V COUT = 1nF VIN = 0V VSHDN = VCC TRANSCONDUCTANCE (µmho) 0 OUTPUT HIGH VOLTAGE (V) 180 108 0 VCC = 5V VOLTAGE GAIN (dB) 9 GAIN 10 PHASE SHIFT (DEG) OUTPUT VOLTAGE (V) 10 20 VCC = 6V TA = 25°C COUT = 1nF IOUT = 0 VSHDN = VCC INPUT OFFSET VOLTAGE (V) 12 11 Input Offset Voltage vs Temperature Gain and Phase Shift vs Frequency DC Transfer Curve IOL = 14µA 0.3 0.2 IOL = 0 0.1 2050 TA = 25°C VOUT = 1/2AVCC VSHDN = VCC 2000 1950 1900 1850 4.5 4.4 –50 –25 25 50 75 0 TEMPERATURE (°C) 100 125 1340 G04 0 –50 –25 25 50 75 0 TEMPERATURE (°C) 100 125 1340 G05 1800 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V) 6.0 6.5 1340 G06 3 LTC1340 U W TYPICAL PERFORMANCE CHARACTERISTICS Transconductance vs Temperature Supply Current vs Supply Voltage 3000 VOUT = 1/2AVCC VSHDN = VCC 2600 SUPPLY CURRENT (µA) 2200 2000 1800 VCC = 5V 1600 TA = 25°C VSHDN = VCC 800 VCC = 6V 2400 700 VCC = 2.7V VSHDN = VCC 650 SUPPLY CURRENT (µA) 2800 TRANSCONDUCTANCE (µmho) Supply Current vs Temperature 900 700 600 500 400 VCC = 6V 600 VCC = 5V 550 500 450 400 1400 VCC = 2.7V 300 1200 1000 –50 350 200 –25 25 50 75 0 TEMPERATURE (°C) 100 125 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V) 6.0 DATA TAKEN ON LTC DEMO BOARD DC152 –40 –50 –60 –66 –70 LTC1340 –80 22.5 VIN = VSHDN = VCC = 5V 20.0 17.5 15.0 12.5 10.0 7.50 5.0 1000 100 10 1.50 0 –50 –90 0 125 10000 AVCC = 5V COUT = 1nF INPUT BIAS CURRENT (pA) –30 OUTPUT VOLTAGE NOISE (µV/RMS) RELATIVE POWER (dB) –20 MEASUREMENT BANDWIDTH 100kHz 100 Input Bias Current vs Temperature 25.0 10 MEASUREMENT BANDWIDTH 30kHz 25 50 75 0 TEMPERATURE (°C) 1340 G09 Output Voltage Noise vs Temperature GSM 900 MS Spectrum Due to Modulation 0 –25 1340 G08 1340 G07 –10 300 –50 6.5 200 400 600 1200 1800 3000 6000 FREQUENCY FROM THE CARRIER(kHz) –25 25 50 75 0 TEMPERATURE (°C) 100 125 1 –50 –25 25 50 75 0 TEMPERATURE (°C) 100 1340 G12 1340 G11 1340 G10 Shutdown Input Threshold vs Temperature 125 Rail-to-Rail Step Response at VCC = 2.7V Rail-to-Rail Step Response at VCC = 6V SHUTDOWN INPUT THRESHOLD (V) 2.4 2.2 VCC = 6V 2.0 VCC = 5V 1.8 1.6 VCC = 4V 1.4 VCC = 3V 0V 0V 1.2 VCC = 2.7V 1.0 0.8 –50 –25 25 50 75 0 TEMPERATURE (°C) VIN = 0.3V TO 6V COUT = 1nF 100 125 1340 G13 4 1340 G14 VIN = 0.3V TO 2.6V COUT = 1nF 1340 G15 LTC1340 U W TYPICAL PERFORMANCE CHARACTERISTICS Charge Pump Frequency vs Temperature Small-Signal Response Large-Signal Response 4.0 VSHDN = VCC COUT = 0pF FREQUENCY (MHz) 3.8 3.6 VCC = 6V COUT = 220pF VCC = 5V COUT = 470pF VCC = 2.7V 3.4 0V COUT = 1nF 3.2 3.0 –50 VIN = 0.5V TO 2V VCC = 2.7V COUT = 1nF –25 25 50 75 0 TEMPERATURE (°C) 100 1340 G18 1340 G17 125 1340 G16 U U U PIN FUNCTIONS CP (Pin 1): Charge Pump Output. This is the output of the internal charge pump. The voltage at CP is nominally twice the VCC input voltage. Connect CP to an external 0.1µF filter capacitor and AVCC. VCC (Pin 2): Supply Input. This is the input supply to the charge pump. VCC can range from 2.7V to 6V and requires a 0.1µF bypass capacitor to PGND. SHDN (Pin 3) Shutdown. If SHDN is high (>VCC – 0.5V), the LTC1340 operates normally. If SHDN is pulled low (< 0.5V), the LTC1340 enters shutdown mode and the supply current drops to less than 1µA typically. In shutdown, the charge pump output voltage collapses and the OUT pin enters a high impedance state. If SHDN returns high, the charge pump output requires 1.2ms typically to resume full voltage. PGND (Pin 4): Power Ground. This is the charge pump ground. Connect PGND to the system power supply return. IN (Pin 5): Signal Input. The internal amplifier amplifies the signal input at this pin typically by 2.3 to the OUT pin. IN accepts signals from GND to VCC without phase reversal or unusual behavior, allowing a direct connection to the output of virtually any phase detector or loop filter powered from VCC. AGND (Pin 6): Signal Ground. Connect AGND to the ground plane in close proximity to the VCO ground. There is an internal parasitic resistance of 50Ω between AGND and PGND. OUT (Pin 7): Driver Output. OUT is the output of the internal gm amplifier and the internal feedback network. It swings from GND to AVCC, and drives a varactor load directly. The OUT pin requires an external capacitor (≥ 220pF) to AGND to ensure stability. OUT typically sinks or sources 20µA. AVCC (Pin 8): Amplifier Supply. LTC recommends a direct connection from AVCC to CP and also recommends a 0.1µF filter capacitor from CP to PGND. 5 LTC1340 W BLOCK DIAGRAM CCP 0.1µF (EXTERNAL) AVCC CP 47.9pF LTC1340 PGND VCC 0.1µF SHDN DOUBLER CHARGE PUMP WITH INTERNAL FLYING CAPACITOR – 1.15M 62.3pF 50Ω VS 0.62V 1.5M + + – OUT ±20µA COUT (EXTERNAL) AGND PGND IN 1340 BD U W U U APPLICATIONS INFORMATION Overview The LTC1340 is a monolithic IC that combines a charge pump and a low noise amplifier to provide a 0V to 5V swing to drive a varactor diode-based PLL system from a single 3V supply. Traditional PLL frequency synthesizers used in cellular phones and other portable RF systems use varactor diodes as the voltage variable element in the VCO. Typical varactor diodes require at least 4V of control voltage swing to obtain their full range of capacitance adjustment. Newer battery-powered systems, operating from low voltage power supplies, have trouble providing this bias voltage without an additional step-up circuit. The LTC1340 design provides a 5V signal swing suitable for biasing such a varactor diode when powered from a 3V or higher voltage supply. The internal op amp and feedback network with built-in offset provide a gain of 2.3 so that a 0.35V to 2.5V swing at the noninverting input provides a 0V to 5V swing at the output. The onboard charge pump provides the boosted voltage necessary to drive the varactor and requires only a single 0.1µF output filter capacitor to complete the boost circuit. The amplifier requires one capacitor (typically 1nF) at its output to set amplifier noise bandwidth and to ensure amplifier stability. The performance characteristics of the LTC1340 are designed to meet the requirements of GSM and similar cellular phone transceivers without requiring additional circuitry. The LTC1340’s high level of functional integra- 6 tion allows it to replace several power supply and regulator components in a typical PLL synthesizer. This results in significant space and complexity savings. Charge Pump The LTC1340 features a self-contained doubling charge pump with internal flying capacitors. The charge pump refreshes the output on each phase of the internal 2MHz clock, giving an effective 4MHz switching frequency. An external 0.1µF capacitor at the CP pin acts as a charge reservoir and provides filtering to minimize clock feedthrough to the amplifier section. The CP pin can be connected directly to the amplifier power supply at AVCC. In addition, it can be filtered with an RC or LC network prior to its connection to AVCC. The LTC1340 minimizes interaction between the charge pump and the amplifier through careful internal shielding. Amplifier The LTC1340 includes an internal gm amplifier with an onchip feedback network to amplify the input signal to the gained output level. The amplifier requires an external capacitor from its output to AGND to provide closed-loop stability, noise bandwidth limiting and to further reduce charge pump feedthrough. The – 3dB signal bandwidth of the amplifier is given by the following equation: BW–3dB = gm/(2π)( COUT)(AV) LTC1340 U U W U APPLICATIONS INFORMATION Amplifier transconductance is typically 1800µmho. With a 1nF external capacitor at the amplifier output, the bandwidth is 125kHz. The amplifier transconductance varies with temperature and process. The minimum recommended COUT is 220pF with a typical bandwidth of 566kHz. should require no additional filtering. Additional filtering to reduce feedthrough noise is possible by inserting a resistor or a ferrite bead between OUT and COUT. The slew rate of the amplifier is: The two sections of the LTC1340 are carefully shielded from each other inside the chip, but care must also be taken in the external hookup to minimize noise at the amplifier output. The two halves of the chip should only meet electrically where the CP and AVCC pins connect together and at the common point of AGND and PGND. Separate PGND and AGND as much as possible. AGND is the amplifier ground. Connect it to a ground plane and as close to the VCO ground as possible. Bypass VCC and CP to PGND with a 0.1µF capacitor. Select high quality, low ESR and low ESL surface mount ceramic capacitors for both the CP and the VCC bypass capacitors. Poor grade capacitors will result in unacceptable ripple amplitude or ringing characteristics. Connect both terminals of the bypass capacitors as close to the chip as possible to minimize charge pump output ripple amplitude and ground currents in the rest of the system. Keep IN and OUT away from VCC, CP and AVCC as much as possible. Crosstalk from VCC, CP and AVCC PCB traces to IN and OUT PCB traces can be minimized by routing AGND PCB traces as shield as shown in Figures 1 and 2. Connect the 1nF output capacitor close to the varactor diode and return it to the AGND plane. The SHDN and IN pins, should not be allowed to go below PGND potential as the ESD diode forms an NPN and bleeds the charge pump output. SR = IOUT/COUT The amplifier typically sinks or sources 20µA, allowing it to slew a 1nF output capacitance at 20V/ms, or 5V in 250µs. The on-chip amplifier feedback network is set for a DC gain of 2.3 with an input offset of 0.35V as shown in the typical curves. The amplifier allows a rail-to-rail input swing with a 3V supply and provides a 5V swing at the output. The output swings to within millivolts of the AVCC voltage and to about 100mV above AGND. The input stage of the amplifier is powered from AVCC and accepts full GND to VCC rail-to-rail input signals without exceeding the input common mode range. The output noise of the amplifier is typically 15µVRMS at frequencies between 1kHz and 100kHz. There are two feedthrough signals at the amplifier OUT pin from the charge pump, the main component at 4MHz and the second harmonic signal at 8MHz. The 4MHz feedthrough is typically below 50µV with COUT equal to 1nF and CCP equal to 0.1µF. The feedthrough signal decreases in amplitude when larger COUT is used. Most systems Hookup LTC1340CS8 PIN 1 0.1µF 0.1µF 1nF VARACTOR DIODE 1340 F01 Figure 1. Suggested Surface Mount PCB Layout for LTC1340CS8 Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 7 LTC1340 U U W U APPLICATIONS INFORMATION 0.1µF PIN 1 0.1µF VARACTOR DIODE 1nF LTC1340CMS8 1340 F02 Figure 2. Suggested Surface Mount PCB Layout for LTC1340CMS8 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. MS8 Package 8-Lead Plastic MSOP (LTC DWG # 05-08-1660) 0.040 ± 0.006 (1.02 ± 0.15) 0.007 (0.18) 0.118 ± 0.004* (3.00 ± 0.10) 0.006 ± 0.004 (0.15 ± 0.10) 8 7 6 5 0° – 6° TYP SEATING PLANE 0.021 ± 0.004 (0.53 ± 0.01) 0.012 (0.30) 0.118 ± 0.004** (3.00 ± 0.10) 0.192 ± 0.004 (4.88 ± 0.10) 0.025 (0.65) TYP 1 2 3 4 * DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE ** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE MSOP08 0596 S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) 0.189 – 0.197* (4.801 – 5.004) (LTC DWG # 05-08-1610) 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0.053 – 0.069 (1.346 – 1.752) 0°– 8° TYP 0.016 – 0.050 0.406 – 1.270 0.014 – 0.019 (0.355 – 0.483) *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 8 7 6 5 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) BSC 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 1 2 3 4 SO8 0695 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1261, LTC1429, LTC1550, LTC1551 GaAs FET Bias Generators Regulated negative voltage generator from a single positive supply 8 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 ● (408) 432-1900 FAX: (408) 434-0507● TELEX: 499-3977 ● www.linear-tech.com 1340f LT/TP 0697 7K • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 1997