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參數(shù)資料
| 型號： | REF195GSZ |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 基準(zhǔn)電壓源/電流源 |
| 英文描述： | Precision Micropower, Low Dropout Voltage References |
| 中文描述： | 1-OUTPUT THREE TERM VOLTAGE REFERENCE, 5 V, PDSO8 |
| 封裝： | ROHS COMPLIANT, MS-012AA, SOIC-8 |
| 文件頁數(shù)： | 20/28頁 |
| 文件大?。?/td> | 407K |
| 代理商： | REF195GSZ |
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REF19x Series
Rev. I | Page 20 of 28
ON
OFF
10k
1k
5%
NC
NC
OUTPUT
V
IN
NC
NC
REF19x
NC = NO CONNECT
8
7
6
5
1
2
3
4
1μF
TANT
+
0
Figure 22. 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 is 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 23. Full-time current
limiting is used to protect the pass transistor against shorts.
U1
REF196
(SEE TABLE)
R4
2
R1
1k
R2
1.5k
Q2
2N3906
+
C2
100μF
25V
D1
R3
1.82k
C1
10μF/25V
(TANTALUM)
S
F
C3
0.1μF
F
S
R1
Q1
TIP32A
(SEE TEXT)
+V
= 6V
TO 9V
(SEE TEXT)
V
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
2
6
1N4148
(SEE TEXT
ON SLEEP)
3
+
4
0
Figure 23. Boosted 3.3 V Referenced with Current Limiting
In this circuit, the power supply current of reference U1 flowing
through R1 to 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 to 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 the drive to Q1 at about 300 mA of load current,
with values as shown in Figure 23. With this separation of
control and power functions, dc stability is optimum, allowing
most advantageous use of premium grade REF19x devices for
U1. Of course, load management should still be exercised. A
short, heavy, low dc resistance (DCR) conductor should be used
from U1 to U6 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
voltage circuit is raised about 1.1 V over that of the REF19x
devices, 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 maximum
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 equivalent
series resistance (ESR), 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 an option, and when
used, some cautions are needed. Due to the additional active
devices in the V
S
line to U1, a direct drive to Pin 3 does not
work as with an unbuffered REF19x device. To enable shutdown
control, the connection from U1 to U2 is broken at the X, and
Diode D1 then allows a CMOS control source, V
C
, to drive U1
to U3 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.
NEGATIVE PRECISION REFERENCE WITHOUT
PRECISION RESISTORS
In many current-output CMOS DAC applications where the
output signal voltage must be the same polarity as the reference
voltage, it is often necessary to reconfigure a current-switching
DAC into a voltage-switching DAC using a 1.25 V reference, an
op amp, and a pair of resistors. Using a current-switching DAC
directly requires an additional operational amplifier at the
output to reinvert the signal. A negative voltage reference is
then desirable, because an additional operational amplifier is
not required for either reinversion (current-switching mode) or
amplification (voltage-switching mode) of the DAC output
voltage. In general, any positive voltage reference can be
converted into a negative voltage reference using an operational
amplifier and a pair of matched resistors in an inverting
configuration. The disadvantage to this approach is that the
largest single source of error in the circuit is the relative
matching of the resistors used.
The circuit illustrated in Figure 24 avoids the need for tightly
matched resistors by using an active integrator circuit. In this
circuit, the output of the voltage reference provides the input
drive for the integrator. To maintain circuit equilibrium, the
integrator adjusts its output to establish the proper relationship
between the reference’s V
OUT
and GND. Thus, any desired
negative output voltage can be selected by substituting for the
appropriate reference IC. The sleep feature is maintained in the
circuit with the simple addition of a PNP transistor and a 10 kΩ
resistor.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| REF195GSZ | 制造商:Analog Devices 功能描述:Voltage Reference IC |
| REF195GSZ-REEL | 功能描述:IC VREF SERIES PREC 5V 8-SOIC RoHS:是 類別:集成電路 (IC) >> PMIC - 電壓基準(zhǔn) 系列:REF19 產(chǎn)品培訓(xùn)模塊:Voltage Reference Basics 標(biāo)準(zhǔn)包裝:100 系列:- 基準(zhǔn)類型:旁路，精度 輸出電壓:4.096V 容差:±0.075% 溫度系數(shù):50ppm/°C 輸入電壓:- 通道數(shù):1 電流 - 陰極:1µA 電流 - 靜態(tài):- 電流 - 輸出:10mA 工作溫度:0°C ~ 70°C 安裝類型:表面貼裝 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 供應(yīng)商設(shè)備封裝:8-SOIC 包裝:管件 |
| REF195GSZ-REEL7 | 功能描述:IC VREF SERIES PREC 5V 8-SOIC RoHS:是 類別:集成電路 (IC) >> PMIC - 電壓基準(zhǔn) 系列:REF19 產(chǎn)品培訓(xùn)模塊:Voltage Reference Basics 標(biāo)準(zhǔn)包裝:100 系列:- 基準(zhǔn)類型:旁路，精度 輸出電壓:4.096V 容差:±0.075% 溫度系數(shù):50ppm/°C 輸入電壓:- 通道數(shù):1 電流 - 陰極:1µA 電流 - 靜態(tài):- 電流 - 輸出:10mA 工作溫度:0°C ~ 70°C 安裝類型:表面貼裝 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 供應(yīng)商設(shè)備封裝:8-SOIC 包裝:管件 |
| REF196 | 制造商:AD 制造商全稱:Analog Devices 功能描述:Precision Micropower, Low Dropout Voltage References |
| REF196ES | 制造商:AD 制造商全稱:Analog Devices 功能描述:Precision Micropower, Low Dropout, Voltage References |
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