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LTC1340 Low Noise, Voltage-Boosted Varactor Driver
FEATURES
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DESCRIPTION
The LTC(R)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 15VRMS, minimizing frequency deviation in PLL frequency synthesizer systems. Supply current is 400A typically with a 3V supply, and drops to 1A 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 20A, 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: 400A at 3V Supply Shutdown Mode Drops Supply Current Below 1A Low Output Noise: 15VRMS 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
APPLICATIONS
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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.
TYPICAL APPLICATION
Low Voltage Frequency Synthesizer
3V
Spectral Plot of VCO Output Driven by LTC1340 Resolution Bandwidth = 300Hz
0dB VCC = 3V COUT = 270pF
0.1F
2 VCC 5 IN LOOP FILTER
1 CP LTC1340
8 AVCC
0.1F
PHASE DETECTOR
OUT 7 0V TO 5V AV = 2.3 270pF
VCO
SHDN PGND AGND 4 3 6
1340 TA01
SHUTDOWN
RELATIVE POWER (10dB/DIV)
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900MHz FREQUENCY (120kHz/DIV)
1340 TA02
1
LTC1340
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 ................. 0C to 70C Extended Commercial Operating Temperature Range (Note 1) ............. - 40C to 85C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec.)................. 300C
PACKAGE/ORDER INFORMATION
TOP VIEW CP VCC SHDN PGND 1 2 3 4 8 7 6 5 AVCC OUT AGND IN
ORDER PART NUMBER LTC1340CMS8 MS8 PART MARKING LTBM
MS8 PACKAGE 8-LEAD PLASTIC MSOP
TJMAX = 125C, JA = 200C/ W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS TA = 25C, unless otherwise noted. (Note 1)
SYMBOL PARAMETER VCC ICC VOL VOH Input Supply Voltage Supply Current Low Output Voltage Swing High Output Voltage Swing IOUT = 0, 2.7V VCC 6V Shutdown, 2.7V VCC 6V VCC = 2.7V, 6V, IOUT = 0A VCC = 2.7V, 6V, IOUT = 14A VCC = 2.7V, IOUT = 0A VCC = 6V, IOUT = 0A VCC = 2.7V, IOUT = 14A VCC = 6V, IOUT = 14A 0.6V VOUT 4.25V, VCC = 2.7V 0.6V VOUT 9.75V, VCC = 6V COUT = 1nF, VOUT = 4V 0.1V VIN VCC
q q
CONDITIONS
q q q q q q q q q q q q q
I OUT t OUT VIN IB VOS AV gm ROUT en BW PSRR ISHDN
Output Sink/Source Current Output Transition Time Input Voltage Range Input Bias Current Input Offset Voltage Amplifier Gain Amplifier Transconductance Output Impedance Output Noise Voltage - 3dB Signal Bandwidth Power Supply Rejection Ratio Shutdown Logic Input Current
VIN = 1V, AVCC = 5V VOUT = 2.5V, AVCC = 5V VOUT = 2.5V, AVCC = 5V VOUT = 1/2AVCC 1kHz to 100kHz, COUT = 1nF COUT = 1nF AVCC = 4V to 6V, COUT = 1nF 0.1V VSHDN VCC
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TOP VIEW CP 1 VCC 2 SHDN 3 PGND 4 8 AVCC 7 OUT 6 AGND 5 IN
ORDER PART NUMBER LTC1340CS8 S8 PART MARKING 1340
S8 PACKAGE 8-LEAD PLASTIC SO
TJMAX = 125C, JA = 130C/ W
MIN 2.7
TYP 500 1
MAX 6 900 10 0.25 0.6
UNITS V A A V V V V V V
4.6 10.5 4.25 9.75 14 14 0 0.01 0.15 2.1 1200 800 0.35 2.3 1800 1 15 125 25 20 20 200 35 35 285 VCC 1 10 0.60 2.5 2300 3200
A A s V nA nA V V/V mho mho M VRMS kHz dB
q q
q
60
90 0.01 1
A
LTC1340
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER tSTART VRIPPLE f CP Charge Pump Start-Up Time Charge Pump Output Ripple at CP Charge Pump Frequency
TA = 25C, unless otherwise noted. (Note 1)
MIN
q
CONDITIONS CCP = 0.1F, VCC = 2.7V, IOUT = 0 CCP = CVCC = 0.1F, VCC = 2.7V, IOUT = 0 (Note 2) (Note 3)
q
TYP 1.2 200
MAX 5
UNITS ms VP-P MHz
2.5
4
The q denotes specifications which apply over the specified temperature range. Note 1: C grade device specifications are guaranteed over the 0C to 70C temperature range. In addition, C grade device specifications are assured over the - 40C to 85C temperature range by design or correlation, but are not production tested.
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 0.1F 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.
TYPICAL PERFORMANCE CHARACTERISTICS
DC Transfer Curve
12 11 10 9 8 7 6 5 4 3 2 1 0 0 1 2 3 4 INPUT VOLTAGE (V) 5 6
1340 G01
INPUT OFFSET VOLTAGE (V)
OUTPUT VOLTAGE (V)
VOLTAGE GAIN (dB)
TA = 25C COUT = 1nF IOUT = 0 VSHDN = VCC
Output High Voltage vs Temperature
9.4 9.3 IOH = 0, VCC = 5V IOH = 14A, VCC = 5V COUT = 1nF VIN = VSHDN = VCC IOH = 0, VCC = 2.7V 9.2 9.1 9.0 8.9 4.9 4.8 4.7 4.6 4.5 4.4 -50 -25 25 50 75 0 TEMPERATURE (C) 100 125 IOH = 14A, VCC = 2.7V
OUTPUT HIGH VOLTAGE (V)
OUTPUT LOW VOLTAGE (V)
0.4
TRANSCONDUCTANCE (mho)
UW
VCC = 6V VCC = 5V VCC = 2.7V
1340 G04
Gain and Phase Shift vs Frequency
20 10 0 -10 -20 -30 -40 -50 -60 -70 -80 -90 1 10 100 FREQUENCY (kHz) VCC = 2.7V TA = 25C COUT = 1nF PHASE GAIN 180 144 108 72 36 0 -36 -72 -108 -144 -180 -216 1000
1340 G02
Input Offset Voltage vs Temperature
0.60 0.55 0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 -50 -25 25 50 75 0 TEMPERATURE (C) 100 125 VCC = 2.7V TO 6V COUT = 1nF VSHDN = VCC
PHASE SHIFT (DEG)
1340 G03
Output Low Voltage vs Temperature
0.5 VCC = 2.7V OR 5V COUT = 1nF VIN = 0V VSHDN = VCC IOL = 14A
2100 2050 2000 1950 1900 1850 1800
Transconductance vs Supply Voltage
TA = 25C VOUT = 1/2AVCC VSHDN = VCC
0.3
0.2 IOL = 0 0.1
0 -50
-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
6.5
1340 G05
1340 G06
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LTC1340 TYPICAL PERFORMANCE CHARACTERISTICS
Transconductance vs Temperature
3000 2800
TRANSCONDUCTANCE (mho)
VOUT = 1/2AVCC VSHDN = VCC
2600 2400 2200 2000 1800 1600 1400 1200 1000 -50 -25
SUPPLY CURRENT (A)
700 600 500 400 300 200
SUPPLY CURRENT (A)
VCC = 6V
VCC = 5V VCC = 2.7V
25 50 75 0 TEMPERATURE (C)
GSM 900 MS Spectrum Due to Modulation
10 25.0
OUTPUT VOLTAGE NOISE (V/RMS)
0 -10
INPUT BIAS CURRENT (pA)
RELATIVE POWER (dB)
-20 -30 -40 -50 -60 -66 -70 -80 -90 0
MEASUREMENT BANDWIDTH 30kHz
MEASUREMENT BANDWIDTH 100kHz
DATA TAKEN ON LTC DEMO BOARD DC152
LTC1340 200 400 600 1200 1800 3000 6000 FREQUENCY FROM THE CARRIER(kHz)
1340 G10
Shutdown Input Threshold vs Temperature
2.4
SHUTDOWN INPUT THRESHOLD (V)
2.2 2.0 1.8 1.6 1.4
VCC = 6V VCC = 5V VCC = 4V VCC = 3V 0V VIN = 0.3V TO 6V COUT = 1nF 125 0V VIN = 0.3V TO 2.6V COUT = 1nF
1.2 1.0 0.8 -50 VCC = 2.7V
1340 G14 1340 G15
-25
25 50 75 0 TEMPERATURE (C)
4
UW
100
1340 G07
Supply Current vs Supply Voltage
900 800 TA = 25C VSHDN = VCC 700 650 600 550 500 450 400
Supply Current vs Temperature
VSHDN = VCC VCC = 6V
VCC = 5V
VCC = 2.7V 350 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V) 6.0 6.5 300 -50
125
-25
25 50 75 0 TEMPERATURE (C)
100
125
1340 G08
1340 G09
Output Voltage Noise vs Temperature
10000
AVCC = 5V COUT = 1nF 22.5 20.0 17.5 15.0 12.5 10.0 7.50 5.0 1.50 0 -50 -25 25 50 75 0 TEMPERATURE (C) 100 125
Input Bias Current vs Temperature
VIN = VSHDN = VCC = 5V 1000
100
10
1 -50
-25
25 50 75 0 TEMPERATURE (C)
100
125
1340 G11
1340 G12
Rail-to-Rail Step Response at VCC = 6V
Rail-to-Rail Step Response at VCC = 2.7V
100
1340 G13
LTC1340 TYPICAL PERFORMANCE CHARACTERISTICS
Charge Pump Frequency vs Temperature
4.0 VSHDN = VCC 3.8
FREQUENCY (MHz)
VCC = 6V VCC = 5V VCC = 2.7V COUT = 220pF COUT = 470pF 0V COUT = 1nF VIN = 0.5V TO 2V VCC = 2.7V COUT = 1nF -25 25 50 75 0 TEMPERATURE (C) 100 125
3.6
3.4
3.2
1340 G18
3.0 -50
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 0.1F 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 0.1F 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 1A 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 50 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 20A. AVCC (Pin 8): Amplifier Supply. LTC recommends a direct connection from AVCC to CP and also recommends a 0.1F filter capacitor from CP to PGND.
UW
1340 G16
Large-Signal Response
COUT = 0pF
Small-Signal Response
1340 G17
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LTC1340
BLOCK DIAGRAM
CCP 0.1F (EXTERNAL) PGND
0.1F SHDN
62.3pF VS 0.62V
1.15M
50
+ -
PGND
IN
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 0.1F 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 integration 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 0.1F 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/(2)( COUT)(AV)
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+
-
VCC
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CP LTC1340 AVCC 47.9pF DOUBLER CHARGE PUMP WITH INTERNAL FLYING CAPACITOR 1.5M OUT 20A COUT (EXTERNAL) AGND
1340 BD
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LTC1340
APPLICATIONS INFORMATION
Amplifier transconductance is typically 1800mho. 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. The slew rate of the amplifier is: SR = IOUT/COUT The amplifier typically sinks or sources 20A, allowing it to slew a 1nF output capacitance at 20V/ms, or 5V in 250s. 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 15VRMS 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 50V with COUT equal to 1nF and CCP equal to 0.1F. The feedthrough signal decreases in amplitude when larger COUT is used. Most systems 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. Hookup 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 0.1F 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.
LTC1340CS8
PIN 1
0.1F
0.1F
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.
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1nF
VARACTOR DIODE
1340 F01
7
LTC1340
APPLICATIONS INFORMATION
0.1F
0.1F
PIN 1
LTC1340CMS8
Figure 2. Suggested Surface Mount PCB Layout for LTC1340CMS8
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) 0.006 0.004 (0.15 0.10) 0.192 0.004 (4.88 0.10) 0.025 (0.65) TYP 1 23 4 0.118 0.004* (3.00 0.10) 8 76 5
0.007 (0.18) 0.021 0.004 (0.53 0.01)
0 - 6 TYP SEATING PLANE 0.118 0.004** (3.00 0.10)
* 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
S8 Package 8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0- 8 TYP 0.053 - 0.069 (1.346 - 1.752) 8 0.004 - 0.010 (0.101 - 0.254) 0.228 - 0.244 (5.791 - 6.197) 0.150 - 0.157** (3.810 - 3.988) 0.189 - 0.197* (4.801 - 5.004) 7 6 5
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
RELATED PARTS
PART NUMBER LTC1261, LTC1429, LTC1550, LTC1551 DESCRIPTION GaAs FET Bias Generators COMMENTS Regulated negative voltage generator from a single positive supply
8
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417 q (408) 432-1900 FAX: (408) 434-0507q TELEX: 499-3977 q www.linear-tech.com
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1nF
VARACTOR DIODE
1340 F02
0.012 (0.30)
MSOP08 0596
0.050 (1.270) BSC
1
2
3
4
SO8 0695
1340f LT/TP 0697 7K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1997

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