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REF01 View Datasheet(PDF) - Analog Devices

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REF01 Datasheet PDF : 20 Pages
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REF01/REF02/REF03
THEORY OF OPERATION
REF01, REF02, and REF03 are high precision, low drift 10.0 V,
5.0 V, and 2.5 V voltage references available in a variety of
packages. These devices are standard band gap references (see
Figure 33). The band gap cell contains two NPN transistors
(Q18 and Q19) that differ in emitter area by a factor of 2. The
difference in the VBE values of these transistors produces a
proportional-to-absolute temperature current (PTAT) through
R14, and, when combined with the VBE of Q19, produces a band
gap voltage, VBG, that is almost constant over temperature.
With an internal op amp and the feedback network created by
R5 and R6, VO is set precisely at 10.0 V, 5.0 V, or 2.5 V. Precision
laser trimming of various resistors and other proprietary circuit
techniques are used to further enhance the initial accuracy,
temperature curvature, and drift performance of the device.
The PTAT voltage is brought out directly from the band gap,
unbuffered, at the TEMP pin. Since this voltage output has a
stable 1.96 mV/°C temperature coefficient, users can estimate
the temperature change of the device by simply monitoring the
change in voltage at this pin.
R1
R2
R3
Q1
Q2 Q7
Q8
Q3
D1
D2
Q4
Q23
VIN
R4
Q9
Q10
VO
D3
C1
Q13
Q12
R12
R13
Q14 Q15
R5
I1
R20
TRIM
Q18
R27
TEMP R14
Q19
Q16
R32
R24
R17 R11
VBG
Q17
Q20
R6
R41
R42
GND
Figure 33. REF0x Simplified Schematic
INPUT AND OUTPUT CAPACITORS
Figure 34 shows the basic input/output capacitor configuration
for the REF0x series of references.
U1
VIN
C1
0.1µF
REF01/
REF02/
REF03
VIN VOUT
TEMP TRIM
GND
VO
C2
0.1µF
While the REF0x series of references are designed to function
stably without any external components, connecting a 0.1 μF
ceramic capacitor to the output is highly recommended to
improve stability and filter out low level voltage noise. An
additional 1 μF to 10 μF electrolytic, tantalum, or ceramic
capacitor can be added in parallel to improve transient perfor-
mance in response to sudden changes in load current; however,
the designer should keep in mind that doing so increases the
turn-on time of the device.
A 1 μF to 10 μF electrolytic, tantalum, or ceramic capacitor
can also be connected to the input to improve transient
response in applications where the supply voltage may fluctuate.
An additional 0.1 μF ceramic capacitor should be connected in
parallel to reduce supply noise.
Both input and output capacitors should be mounted as close to
the device pins as possible.
OUTPUT ADJUSTMENT
The REF0x trim terminal can be used to adjust the output
up or down from the internally trimmed, nominal output
voltage. This feature allows the system designer to trim out
system errors due to changes in line and load conditions,
thermal hysteresis, output offset due to solder reflow, or other
error sources. The basic trim circuit configuration is shown
in Figure 35.
Table 7 also lists the range of output voltages obtainable from
each model in this configuration.
U1
REF01/
REF02/
REF03
VIN
VIN VOUT
VO
TEMP TRIM
GND
R1
470k
POT
10k
R2
1k
Figure 35. Optional Trim Adjustment Circuit
Table 7. Adjustment Range Using Trim Circuit
Model
VOUT, Low Limit
VOUT, High Limit
REF01
9.70 V
10.05 V
REF02
4.95 V
5.02 V
REF03
2.3 V
2.8 V
Adjustment of the output does not significantly affect the
temperature performance of the reference itself, provided the
temperature coefficients of the resistors used are low.
Figure 34. Basic REF0x Capacitor Configuration
Rev. K | Page 14 of 20
 

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