LTC1340 Просмотр технического описания (PDF) - Linear Technology

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LTC1340

Low Noise, Voltage-Boosted Varactor Driver

Linear Technology 

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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