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PDF LTC1340CS8 Data sheet ( Hoja de datos )
| Número de pieza | LTC1340CS8 | |
| Descripción | Low Noise/ Voltage-Boosted Varactor Driver | |
| Fabricantes | Linear Technology | |
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FEATURES
s Generates 5V Varactor Drive from a 3V Supply
s Wide Supply Voltage Range: 2.7V to 6V
s Requires Only Three External Components
s Micropower Operation: 400µA at 3V Supply
s Shutdown Mode Drops Supply Current Below 1µA
s Low Output Noise: 15µVRMS
s Amplifier Gain: 2.3
s Up to 500kHz Signal Bandwidth
s MS8 and SO-8 Packages
s Very Low Input Bias Current: 10nA Max
s Amplifier Offset Maintains Phase Detector
in Linear Region
U
APPLICATIONS
s 5V Varactor Drive from a Single Li-Ion Cell
s 5V Varactor Drive from Three NiCd/NiMH Cells
s Cellular Telephones
s Portable RF Equipment
s Radio Modems
s Wireless Data Transmission
, LTC and LT are registered trademarks of Linear Technology Corporation.
LTC1340
Low Noise, Voltage-Boosted
Varactor Driver
DESCRIPTION
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 volt-
ages 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 synthe-
sizer 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 user-
adjustable 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 rail-
to-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.
TYPICAL APPLICATION
Low Voltage Frequency Synthesizer
3V
PHASE
DETECTOR
0.1µF
218
VCC CP AVCC
0.1µF
LTC1340
5 IN
OUT 7 0V TO 5V
LOOP
FILTER
AV = 2.3
SHDN PGND AGND
3 46
270pF
VCO
SHUTDOWN
1340 TA01
Spectral Plot of VCO Output Driven by LTC1340
Resolution Bandwidth = 300Hz
0dB
VCC = 3V
COUT = 270pF
900MHz
FREQUENCY (120kHz/DIV)
1340 TA02
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LTC1340
Charge Pump Frequency vs
Temperature
4.0
VSHDN = VCC
3.8
VCC = 6V
3.6 VCC = 5V
3.4
VCC = 2.7V
3.2
3.0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1340 G16
Large-Signal Response
Small-Signal Response
0V
VIN = 0.5V TO 2V
VCC = 2.7V
COUT = 1nF
COUT = 0pF
COUT = 220pF
COUT = 470pF
COUT = 1nF
1340 G17
1340 G18
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 shut-
down, 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 rever-
sal or unusual behavior, allowing a direct connection to the
output of virtually any phase detector or loop filter pow-
ered 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
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| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet LTC1340CS8.PDF ] | |
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