XR-2209 Datasheet, PDF (5/20 Pages) Exar Corporation – Voltage-Controlled Oscillator

XR-2209
PRECAUTIONS
SYSTEM DESCRIPTION
The following precautions should be observed when
operating the XR-2209 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 pin 4
be limited to  6mA. In addition, permanent damage
to the device may occur if the total timing current
exceeds 10mA.
2. Terminals 2, 3, and 4 have very low internal
impedance and should, therefore, be protected from
accidental shorting to ground or the supply voltage.
The XR-2209 functional blocks are shown in the block
diagram given in Figure 1. They are a voltage controlled
oscillator (VCO), and two buffer amplifiers for triangle and
squarewave outputs. Figure 2 is a simplified XR-2209
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 resistor that is connected
from the timing terminals (pin 4) to ground.
The triangle output buffer has a low impedance output
(10W typ.) while the squarewave is an open-collector
type. An external bias input allows the XR-2209 to be
used in either single or split supply applications.
V_CC
V_CC
S2
I+ _C
R_L
1mF
12
3
V_CC C1
C2
7
SWO
Square Wave
Output
8
TWO
Triangle Wave
XR-2209
Output
BIAS ⁵
V_CC
5.1K
TR
V_EE
4
6
5.1K
1mF
I-
R
S1
Rev. 2.02
Figure 3. Test Circuit for Single Supply Operation
5