XR-2207 Datasheet, PDF (6/24 Pages) Exar Corporation – Voltage-Controlled Oscillator

XR-2207
PRECAUTIONS
The following precautions should be observed when
operating the XR-2207 family of integrated circuits:
1. Pulling excessive current from the timing terminals
will adversely affect the temperature stability of the
circuit. To minimize this disturbance, it is
recommended that the total current drawn from pins
4, 5, 6, and 7 be limited to  6mA. In addition,
permanent damage to the device may occur if the
total timing current exceeds 10mA.
2. Terminals 2, 3, 4, 5, 6 , and 7 have very low internal
impedance and should, therefore, be protected from
accidental shorting to ground or the supply voltage.
3. The keying logic pulse amplitude should not exceed
the supply voltage.
SYSTEM DESCRIPTION
The XR-2207 functional blocks are shown in the block
diagram given in Figure 1. They are a voltage controlled
oscillator (VCO), four current switches which are
controlled by binary keying inputs, and two buffer
amplifiers for triangle and squarewave outputs. Figure 2
is a simplified XR-2207 schematic diagram that shows the
circuit in greater detail.
The VCO is a modified emitter-coupled current controlled
multivibrator. Its oscillation is inversely proportional to the
value of the timing capacitor connected to pins 2 and 3,
and directly proportional to the total timing current I_T. This
current is determined by the resistors that are connected
from the four timing terminals (pins 4, 5, 6 and 7) to
ground, and by the logic levels that are applied to the two
binary keying input terminals (pins 8 and 9). Four different
oscillation frequencies are possible since I_T can have four
different values.
The triangle output buffer has a low impedance output
(10Ω TYP) while the squarewave is an open-collector
type. An external bias input allows the XR-2207 to be
used in either single or split supply applications.
V_CC
V_CC
S2
I+ C
0.1µF
RL
Binary
8
Keying Inputs ₉
0.1µF
10
12
3
V+ C1
C2
A
B
XR-2207
GND
13
SWO
14
TWO
11
BIAS
R1 R 2 R 3 R4 V-
4 5 6 7 12
R1 R2 R3 R4
Square Wave
Output
Triangle Wave
Output
V_CC
5.1K
3.9K
S1
Rev. 2.02
Figure 3. Test Circuit for Single Supply Operation
6