
Precision Single Power Supply
VOLTAGE-TO-FREQUENCY CONVERTER
VFC121
International Airport Industrial Park Mailing Address: PO Box 11400 Tucson, AZ 85734 Street Address: 6730 S. Tucson Blvd. Tucson, AZ 85706
Tel: (520) 746-1111 Twx: 910-952-1111 Cable: BBRCORP Telex: 066-6491 FAX: (520) 889-1510 Immediate Product Info: (800) 548-6132
APPLICATIONS
G
INTEGRATING A/D CONVERSION
G
ANALOG SIGNAL TRANSMISSION
G
PHASE-LOCKED LOOP VCO
G
GALVANICALLY ISOLATED SYSTEMS
FEATURES
G
SINGLE SUPPLY OPERATION:
+4.5V to +36V
G
f
O
= 1.5MHz max
G
LOW NONLINEARITY: 0.03% max at
100kHz, 0.1% max at 1MHz
G
HIGH INPUT IMPEDANCE
G
VOLTAGE REFERENCE OUTPUT
G
THERMOMETER OUTPUT: 1mV/
°
K
DESCRIPTION
The VFC121 is a monolithic voltage-to-frequency
converter consisting of an integrating amplifier, volt-
age reference, and one-shot charge pump circuitry.
High-frequency complementary NPN/PNP circuitry is
used to implement the charge-balance technique,
achieving speed and accuracy far superior to previous
single power supply VFCs.
The high-impedance input accepts signals from ground
potential to V
S
– 2.5V. Power supplies from 4.5V to
36V may be used. A 2.6V reference voltage output
may be used to excite sensors or bias external cir-
cuitry. A thermometer output voltage proportional to
absolute temperature (
°
K) may be used as a tempera-
ture sensor or for temperature compensation of appli-
cations circuits.
Frequency output is an open-collector transistor. A
disable pin forces the output to the high impedance
state, allowing multiple VFCs to share a common
transmission path.
2.6V
V
T
One
Shot
V
REF
V
REF
Comparator
Integrator
I
REF
12
11
10
9
13
2
14
8
6
3
5
4
R
TRIM
+V
S
+5V
Ground
(Optional)
R
PULL UP
V
PULL UP
C
INT
= 2700pF
V
IN
= 0 to +2V
R
BIAS
= 8k
(Optional)
R
IN
R
IN
= 8k
C
OS
= 1200pF
f
OUT
=
0 to 100kHz
1989 Burr-Brown Corporation
PDS-971A
Printed in U.S.A. March, 1992