VFC101JN BURR-BROWN [Burr-Brown Corporation], VFC101JN Datasheet - Page 7

• Manufacturer Part Number: VFC101JN
• Description: Synchronized VOLTAGE-TO-FREQUENCY CONVERTER
• Manufacturer: BURR-BROWN [Burr-Brown Corporation]

tance on the output line. The rising edge of an output pulse
is determined by the RC time constant of the pull-up resistor
and the stray capacitance.
The synchronized nature of the VFC101 makes viewing its
output on an oscilloscope somewhat tricky. Since all output
pulses align with the clock, it is best to trigger and view the
clock on one of the input channels and the output can then
be viewed on another oscilloscope channel. Depending on
the VFC input voltage, the output waveform may appear as
if the oscilloscope is not properly triggered. The output
might best be visualized by imagining a constant output
frequency which is locked to a submultiple of the clock
frequency with occasional extra pulses or missing pulses to
create the necessary average frequency. It is these extra or
missing pulses that make the output waveform appear as if
the oscilloscope is not properly triggered. This behavior
amounts to a frequency or phase jitter in the output, making
frequency detection with most phase-locked loop circuitry
impractical. For the same reason, fast period measurement
(ratiometric counting) will not provide a stable reading. The
output frequency must be measured (averaged) for N counts
of f
SHORTENED OUTPUT PULSES
With pin 12 connected to +V
duration is equal to one period of the clock input. Shorter
output pulses may be useful in driving optical couplers or
transformers for voltage isolation or noise rejection. This
can be accomplished by connecting capacitor C
in Figure 4. Output pulses cannot be made to exceed one
clock period in duration. Thus, a C
create an output pulse which is longer than one period of the
clock will have the same effect as disabling the one-shot,
FIGURE 4. Circuit and Timing Diagram for Shortened Output Pulses.
CLOCK
to achieve a stable N counts of resolution.
One-Shot
Output
+V
+V
CC
CC
Clock
2
12
f
C
OUT
OS
CC
, the negative output pulse
–V
CC
11
OS
0.1µF
value which would
14
15
f
Common
OUT
Digital
OS
as shown
Output Pulse Width With
Pin 12 Connected to +V
1000pF
0.01µF
7
100pF
0.1µF
10pF
1µF
causing the output pulse to last one clock period. The
minimum practical pulse width of the one-shot circuit is
approximately 100ns. Using C
pulses does not affect the output frequency or the gain
equation.
REFERENCE VOLTAGE
Low gain drift is achieved with a precision internal 5V
reference. This reference is brought to an external pin and
can be used for a variety of purposes. It is used to offset the
noninverting comparator input in voltage-to-frequency mode
(although a precise voltage is not required for this function).
It is very useful in many other applications such as offsetting
the input to accept bipolar input signals. It can source up to
10mA and sink 100 A. Heavy loading of the reference will
change the gain of the VFC. A 10mA load interacting with
a 0.5
equation and reference voltage by 0.1%.
LINEARITY PERFORMANCE
The linearity of the VFC100 is specified as the worst-case
deviation from a straight line defined by low scale and high
scale end point measurements. This worst-case deviation is
expressed as a percentage of the 10V full-scale input. All
units are tested.
Linearity performance and gain error change with full-scale
operating frequency as shown in the typical performance
curves. Integrator voltage swing (determined by C
minor effect on linearity. A small integrator voltage swing
typically leads to best linearity performance.
The best linearity performance at high full-scale frequencies
(above 500kHz) is obtained by using short output pulses
100ns
typical output impedance will change the VFC gain
CC
1µs
t
.
O
Nominal Output Pulse Width, t
10µs
100µs
OS
VFC101
to generate shorter output
O
1ms
t
O
10ms
INT
) has a
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