XR2207 Exar Corporation, XR2207 Datasheet - Page 6

• Manufacturer Part Number: XR2207
• Description: Voltage-Controlled Oscillator
• Manufacturer: Exar Corporation

PRECAUTIONS
The following precautions should be observed when
operating the XR-2207 family of integrated circuits:
1. Pulling excessive current from the timing terminals
2. Terminals 2, 3, 4, 5, 6 , and 7 have very low internal
3. The keying logic pulse amplitude should not exceed
XR-2207
will adversely affect the temperature stability of the
circuit. To
recommended that the total current drawn from pins
4, 5, 6, and 7 be limited to
permanent damage to the device may occur if the
total timing current exceeds 10mA.
impedance and should, therefore, be protected from
accidental shorting to ground or the supply voltage.
the supply voltage.
Rev. 2.02
minimize
Keying Inputs
0.1 F
this
Binary
Figure 3. Test Circuit for Single Supply Operation
disturbance,
0.1 F
6mA. In addition,
10
8
9
S1
A
B
GND
V
V+
R1
CC
1
it
R1
R2
C1
I+
4
XR-2207
2
is
R 2
R3 R4
5
C
6
R 3
6
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
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
different values.
The triangle output buffer has a low impedance output
(10
type. An external bias input allows the XR-2207 to be
used in either single or split supply applications.
C2
R4
3
7
TYP) while the squarewave is an open-collector
V-
12
SWO
TWO
BIAS
13
14
11
3.9K
RL
5.1K
S2
Square Wave
Triangle Wave
Output
Output
V
CC
V
CC
T
can have four
T
. This