Sequential PROPHET-600 - Page 75

Absolute Maximum Ratings
pm 16 on the 3345) internally
connects to the control input
of the exponential generator
(base of Q,). This output is a
current and is given by
22V t
•om - < 1 -i c Rz/3.0)
r t
where V T ■ KT/q » 26 mV
& 20 C. and where lc is the
total current flowing into the
frequency control pm and must
remain positive for proper
operation (a negative input
current will produce the same
output as a zero input current).
Since the frequency control
input pm is a virtual ground
summing node, any number of
control voltages may be summed
simply with input resistors to
this pin.
The current output of the
multiplier is converted to the
required drive voltage with a
resistor from the multiplier
output pm to ground. For
greatest multiplier accuracy,
this resistor. R$. should be 1.8k
and the current flowing out
of pin 2. 22 V t /R t . should be
Close to the current flowing
out of pm 1, 3.0/R*.
Since the components asso
dated with tho tempco generator
and multiplier determine the
maximum voltage excursion
possible at the base of Q|. they
should be selected to provide the
desired frequency control range
of the oscillator. The exponen
tial generator itself is capable of
delivering a current for charging
and discharging the timing
capacitor from greater than
5mA down to less than the
input bias current of the buffer,
thus allowing for a typical fre¬
quency range greater than
500,000 1. The most accurate
portion of this current range,
from 50nA to 100#;A, should be
used for the most critical portion
of the desired frequency range.
Consideration of this critical
range determines the value of
Voltage Between Vcc and V EE Pins
♦ 24V.-0.5V
Voltag- Between V C c and Ground Pins ♦ 18V. -0.5V
Voltage Between V EE and Ground Pins -6 0V.«0.5V
Voltage Between Frequency Control Pm
or Reference Current Pm and Ground Pin
16.0V
Voltage Between Multiplier Output Pm
and Ground Pm
♦ 6.0V, -IV
Current through Any Pm
i40mA
Storage Temperature Range
-55°C to *150°C
Operating Temperature Range
-25°C to ♦ 75“C
CEM 3345 Circuit Block and Connection Diagram
Cp. the timing capacitor. The
oscillation frequency is given by
»-3W<VccC f )
where I eg is the output current
from the exponential generator.
If. for instance, the most impor
tant frequency range is from
5H/ to 10kH/. then Cp should
be lOOOpF at V cc • *I5V (a
low leakage, low tempco capac¬
itor. such as mica, should be
used for Cp).
Next the reference current
for the exponential generator
(Current into pin 13 on the
3340. pin 15 on the 3345) is
selected. This current ideally
should be the geometric mean
of the selected generator current
range, but consideration of
the temperature coefficient of
3