LM169BH National Semiconductor, LM169BH Datasheet - Page 5

• Manufacturer Part Number: LM169BH
• Description: Precision Voltage Reference
• Manufacturer: National Semiconductor

Application Hints
The LM169 LM369 can be applied in the same way as any
other voltage reference The adjacent Typical Applications
Circuits suggest various uses for the LM169 LM369 The
LM169 is recommended for applications where the highest
stability and lowest noise is required over the full military
temperature range The LM369 is suitable for limited-tem-
perature operation The curves showing the Noise vs Ca-
pacitance in the Typical Performance Characteristics sec-
tion show graphically that a modest capacitance of 0 1 to
0 3 microfarads can cut the broadband noise down to a lev-
el of only a few microvolts less than 1 ppm of the output
voltage The capacitor used should be a low-leakage type
For the temperature range 0 to 50 C polyester or Mylar
will be suitable but at higher temperatures a premium film
capacitor such as polypropylene is recommended For oper-
ation at
ensure sufficiently low leakage Ceramic capacitors may
seem to do the job but are not recommended for produc-
tion use as the high-K ceramics cannot be guaranteed for
low leakage and may exhibit piezo-electric effects convert-
ing vibration or mechanical stress into excessive electrical
noise
Additionally the inherent superiority of the LM169 369’s
buried Zener diode provides freedom from low-frequency
noise wobble and jitter in the frequency range 0 01 to 10
Hertz where capacitive filtering is not feasible
Pins 1 3 7 and 8 of the LM169 369 are connected to
internal trim circuits which are used to trim the device’s out-
put voltage and Tempco during final testing at the factory
Do not connect anything to these pins or improper opera-
tion may result These pins would not be damaged by a
short to ground or by Electrostatic Discharges however
keep them away from large transients or AC signals as
stray capacitance could couple noises into the output
These pins may be cut off if desired Alternatively a shield
foil can be laid out on the printed circuit board surrounding
these pins and pin 5 and this guard foil can be connected to
ground or to V
coupling and DC leakages
The trim pin (pin 5) should also be guarded away from noise
signals and leakages as it has a sensitivity of 15 millivolts of
Typical Applications
NOTE Pin numbers for H M or N packages
V
out
per microampere The trim pin can also be used in
a
Series Reference
125 C a Teflon capacitor would be required to
out
effectively acting as a guard against AC
TL H 9110–2
Shunt Reference with Optional Trim
5
the circuits shown to provide an output trim range of
millivolts Trimming to a wider range is possible but is not
recommended as it may degrade the Tempco and the
Tempco linearity at temperature extremes For example if
the output were trimmed up to 10 240V the Tempco would
be degraded by 8 ppm C As a general rule Tempco will
be degraded by 1 ppm C per 30 mV of output adjustment
The output can sink current as well as source it but the
output impedance is much better for sourcing current Also
the LM169 369 requires a 0 1
0 1 F in series with 10 ) bypass from the output to ground
for stable operation in shunt mode (output sinking current)
The output has a class-B stage so if the load current chang-
es from sourcing to sinking an output transient will occur
To avoid this transient it may be advisable to preload the
output with a few milliamperes of load to ground The
LM169 369 does have an excellent tolerance of load ca-
pacitance and in cases of load transients electrolytic or
tantalum capacitors in the range 1 to 500 microfarads have
been shown to improve the output impedance without de-
grading the dynamic stability of the device The LM169 369
are rated to drive an output of
cy any load current larger than 1 mA can cause thermal
errors (such as 1 mA
or 2 microvolts) and degrade the ultimate precision of the
output voltage
The output is short-circuit-proof to ground However avoid
overloads at high ambient temperatures as a prolonged
short-circuit may cause the junction temperature to exceed
the Absolute Maximum Temperature The device does not
include a thermal shut-down circuit If the output is pulled to
a positive voltage such as
will be limited but overheating may occur Avoid such over-
loads for voltages higher than
onds or at high ambient temperatures
The LM169 369 has an excellent long-term stability and is
suitable for use in high-resolution Digital Voltmeters or Data
Acquisition systems Its long-term stability is typically 3 to 10
ppm per 1000 hours when held near T
ter when operated at room temperature Contact the factory
for availability of devices with proven long-term stability
TL H 9110 – 3
c
5V
a
15 or
Series Reference with
c
g
for Reduced Noise
a
4 ppm 100 mW
10 mA but for best accura-
Optional Filter
20 V for more than 5 sec-
F tantalum capacitor (or
a
20V the output current
max
and slightly bet-
e
TL H 9110– 4
0 2 ppm
g
10