參數(shù)資料
型號(hào)： REF193ES
廠商： Analog Devices, Inc.
英文描述： Precision Micropower, Low Dropout, Voltage References
中文描述： 精密微功耗，低壓差，電壓基準(zhǔn)
文件頁(yè)數(shù)： 18/23頁(yè)
文件大小： 238K
代理商： REF193ES
REF19x Series
–18–
REV. D
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 16, a membrane ON/OFF switch is used to control the
operation of the reference. During an initial power-on condi-
tion, the SLEEP pin is held to GND by the 10 k
resistor.
Recall that this condition disables (read: three-state) the
REF19x output. When the membrane ON switch is pressed,
the SLEEP pin is momentarily pulled to V
IN
, enabling the
REF19x output. At this point, current through the 10k
is
reduced and the internal current source connected to the
SLEEP pin takes control. Pin 3 assumes and remains at the
same potential as V
IN
. When the membrane OFF switch is
pressed, the SLEEP pin is momentarily connected to GND,
which once again disables the REF19x output.
NC
NC
V
IN
1
2
3
4
8
7
6
5
NC
NC
OUTPUT
ON
OFF
10k
V
1k
V
5%
REF19x
1
F
TANT
Figure 16. Membrane Switch Controlled Power Supply
Current-Boosted References with Current Limiting
While the 30 mA rated output current of the REF19x series is
higher than typical of other reference ICs, it can be boosted to
higher levels if desired, with the addition of a simple external
PNP transistor, as shown in Figure 17. Full time current limit-
ing is used for protection of the pass transistor against shorts.
U1
(SEE TABLE)
R4
2
V
R1
1k
V
R2
1.5k
V
Q2
2N3906
C2
100
m
F/25V
D1
1N4148
(SEE TEXT
ON SLEEP)
R3
1.82k
V
C1
10
m
F/25V
(TANTALUM)
S
F
C3
0.1
m
F
F
S
R1
Q1
TIP32A
(SEE TEXT)
+V
S
= 6 TO 9V
(SEE TEXT)
V
S
COMMON
V
C
V
COMMON
OUTPUT TABLE
U1
REF192
REF193
REF196
REF194
REF195
V
OUT
(V)
2.5
3.0
3.3
4.5
5.0
+V
OUT
3.3V
@ 150mA
Figure 17. A Boosted 3.3 V Reference with Current
Limiting
In this circuit, the power supply current of reference U1 flowing
through R1–R2 develops a base drive for Q1, whose collector
provides the bulk of the output current. With a typical gain of
100 in Q1 for 100 mA–200 mA loads, U1 is never required to
furnish more than a few mA, so this factor minimizes tempera-
ture related drift. Short circuit protection is provided by Q2,
which clamps drive to Q1 at about 300 mA of load current with
values as shown. With this separation of control and power
functions, dc stability is optimum, allowing best advantage use
of premium grade REF19x devices for U1. Of course, load
management should still be exercised. A short, heavy, low DCR
(DC Resistance) conductor should be used from U1–6 to the
V
OUT
sense point “S,” where the collector of Q1 connects to the
load, point “F.”
Because of the current limiting configuration, the dropout volt-
age circuit is raised about 1.1 V over that of the REF19x de-
vices, due to the V
BE
of Q1 and the drop across current sense
resistor R4. However, overall dropout is typically still low
enough to allow operation of a 5 V to 3.3 V regulator/reference
using the REF196 for U1 as noted, with a V
S
as low as 4.5 V
and a load current of 150 mA.
The requirement for a heat sink on Q1 depends on the maxi-
mum input voltage and short circuit current. With V
S
= 5 V
and a 300 mA current limit, the worst case dissipation of Q1 is
1.5 W, less than the TO-220 package 2 W limit. However, if
smaller TO-39 or TO-5 packaged devices such as the 2N4033
are used, the current limit should be reduced to keep maximum
dissipation below the package rating. This is accomplished by
simply raising R4.
A tantalum output capacitor is used at C1 for its low ESR
(Equivalent Series Resistance), and the higher value is required
for stability. Capacitor C2 provides input bypassing and can be
an ordinary electrolytic.
Shutdown control of the booster stage is shown as an option,
and when used some cautions are in order. Because of the
additional active devices in the V
S
line to U1, direct drive to
Pin 3 does not work as with an unbuffered REF19x device. To
enable shutdown control, the connection to U1-2 is broken at
the “X,” and diode D1 then allows a CMOS control source V
C
to drive U1-3 for ON-OFF operation. Startup from shutdown is
not as clean under heavy load as it is in basic REF19x series and
can require several milliseconds under load. Nevertheless, it is
still effective and can fully control 150 mA loads. When shutdown
control is used, heavy capacitive loads should be minimized.
相關(guān)PDF資料
PDF描述
REF193FS Precision Micropower, Low Dropout, Voltage References
REF193GS Precision Micropower, Low Dropout, Voltage References
REF193GRU Precision Micropower, Low Dropout, Voltage References
REF193GBC Precision Micropower, Low Dropout, Voltage References
REF196GRU CONNECTOR ACCESSORY
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
REF193ES3 制造商:未知廠家 制造商全稱:未知廠家 功能描述:REF19x Series: Precision Micropower. Low Dropout. Low Voltage References Data Sheet (Rev. E. 1/03)
REF193FS 制造商:AD 制造商全稱:Analog Devices 功能描述:Precision Micropower, Low Dropout, Voltage References
REF193FS3 制造商:未知廠家 制造商全稱:未知廠家 功能描述:REF19x Series: Precision Micropower. Low Dropout. Low Voltage References Data Sheet (Rev. E. 1/03)
REF193GBC 制造商:AD 制造商全稱:Analog Devices 功能描述:Precision Micropower, Low Dropout, Voltage References
REF193GP 制造商:Rochester Electronics LLC 功能描述:- Bulk
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