TLC2940_06 Datasheet, PDF (2/10 Pages) Texas Instruments – HIGH-PERFORMANCE CMOS VOLTAGE-CONTROLLED OSCILLATOR

TLC2940
HIGH-PERFORMANCE CMOS VOLTAGE-CONTROLLED OSCILLATOR
SLAS244 – OCTOBER 1999
Terminal Functions
TERMINAL
I/O^{
NAME
NO.
DESCRIPTION
BIAS
FREFINPUT
7
M Bias supply terminal for internal VCO. The resistor should be located between VDD and this terminal.
3
I Not used. This terminal should be tied to ground.
GND
5 PS Ground
LOGIC VDD
1 PS Power supply for the internal logic circuitry (PFD portion, input/output portion). It is recommended that this
terminal is separated from the VCO supply voltage terminal.
PFD OUT
4
O Not used. This terminal should be unconnected (open).
VCOIN
6
I VCO control voltage input.
VCO OUT
2
O VCO output. This terminal is tied to a low level at inhibit status.
VCO VDD
8 PS Supply voltage for VCO analog portion.
† _{I: Input, O: Output, PS: Power supply/GND, M: Others}
detailed description
The TLC2940 is an analog VCO IC that generates a frequency that is a multiple of a reference frequency for
a PLL block configuration. Normally, a PLL block is composed of a VCO, a phase frequency detector, counter
logic, and a loop filter.
The following is a description for the analog VCO of the TLC2940.
The built-in analog VCO is composed of a ring oscillator portion for oscillation operation and a bias control
portion to generate a bias level to supply to the ring oscillator. The oscillation operation is performed by a bias
resistor (R_BIAS) connected between the bias control (pin 7) and the supply voltage (pin 8). The VCO oscillation
frequency is determined by this resistor value, R_BIAS, that is, the oscillation frequency decreases as the resistor
value increases, and the oscillation frequency increases as the resistor value decreases. The lock frequency
range is from 35 MHz to 75 MHz with a R_BIAS of 1.5 kΩ to 4.3 kΩ at 5-V operation and from 28 MHz to 50 MHz
with a R_BIAS of 1.5 kΩ to 2.7 kΩ at 3-V operation over the recommended supply voltage and operating free-air
temperature range.
Refer to the curves shown in the typical characteristics section for the lock frequency ranges with varying R_BIAS
values.
VCO Oscillation
VCO Oscillation Frequency Range
Bias Resistor (RBIAS)
VCO Control Voltage (VCOIN)
Figure 1. VCO Oscillation Frequency Range Setting
2
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