REF191 View Datasheet(PDF) - Analog Devices
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REF191 Datasheet PDF : 28 Pages
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APPLICATIONS
OUTPUT SHORT-CIRCUIT BEHAVIOR
The REF19x family of devices is completely protected from
damage due to accidental output shorts to GND or to V+. In the
event of an accidental short-circuit condition, the reference
device shuts down and limits its supply current to 40 mA.
V+
VOUT
SLEEP (SHUTDOWN)
GND
Figure 20. Simplified Schematic
DEVICE POWER DISSIPATION CONSIDERATIONS
The REF19x family of references is capable of delivering load
currents to 30 mA with an input voltage that ranges from
3.3 V to 5 V. When these devices are used in applications with
large input voltages, exercise care to avoid exceeding the
maximum internal power dissipation of these devices.
Exceeding the published specifications for maximum power
dissipation or junction temperature can result in premature
device failure. The following formula should be used to
calculate a device’s maximum junction temperature or
dissipation:
PD
=
TJ − TA
θJA
In this equation, TJ and TA are the junction and ambient
temperatures, respectively; PD is the device power dissipation;
and θJA is the device package thermal resistance.
OUTPUT VOLTAGE BYPASSING
For stable operation, low dropout voltage regulators and
references generally require a bypass capacitor connected from
their VOUT pins to their GND pins. Although the REF19x family
of references is capable of stable operation with capacitive loads
exceeding 100 μF, a 1 μF capacitor is sufficient to guarantee
rated performance. The addition of a 0.1 μF ceramic capacitor
in parallel with the bypass capacitor improves load current
transient performance. For best line voltage transient
performance, it is recommended that the voltage inputs of these
devices be bypassed with a 10 μF electrolytic capacitor in
parallel with a 0.1 μF ceramic capacitor.
REF19x Series
SLEEP MODE OPERATION
All REF19x devices include a sleep capability that is
TTL/CMOS-level compatible. Internally, a pull-up current
source to VIN is connected at the SLEEP pin. This permits the
SLEEP pin to be driven from an open collector/drain driver. A
logic low or a 0 V condition on the SLEEP pin is required to
turn off the output stage. During sleep, the output of the
references becomes a high impedance state where its potential
would then be determined by external circuitry. If the sleep
feature is not used, it is recommended that the SLEEP pin be
connected to VIN (Pin 2).
BASIC VOLTAGE REFERENCE CONNECTIONS
The circuit in Figure 21 illustrates the basic configuration for
the REF19x family of references. Note the 10 μF/0.1 μF bypass
network on the input and the 1 μF/0.1 μF bypass network on
the output. It is recommended that no connections be made to
Pin 1, Pin 5, Pin 7, and Pin 8. If the sleep feature is not required,
Pin 3 should be connected to VIN.
10µF
REF19x
NC 1
VIN 2
0.1µF SLEEP 3
8 NC
7 NC
OUTPUT
6
4
5 NC
+1µF
TANT
NC = NO CONNECT
Figure 21. Basic Voltage Reference Configuration
0.1µF
MEMBRANE SWITCH-CONTROLLED POWER
SUPPLY
With output load currents in the tens of mA, the REF19x family
of references can operate as a low dropout power supply in
hand-held instrument applications. In the circuit shown in
Figure 22, a membrane on/off switch is used to control the
operation of the reference. During an initial power-on condition,
the SLEEP pin is held to GND by the 10 kΩ resistor. Recall that
this condition (read: three-state) disables the REF19x output.
When the membrane on switch is pressed, the SLEEP pin is
momentarily pulled to VIN, enabling the REF19x output. At this
point, current through the 10 kΩ resistor is reduced, and the
internal current source connected to the SLEEP pin takes
control. Pin 3 assumes and remains at the same potential as VIN.
When the membrane off switch is pressed, the SLEEP pin is
momentarily connected to GND, which once again disables the
REF19x output.
Rev. I | Page 19 of 28
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