Datasheet ADR430, ADR431, ADR433, ADR434, ADR435 (Analog Devices) - 18

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ADR430/ADR431/ADR433/ADR434/ADR435 Data Sheet VIN RLW PROGRAMMABLE CURRENT SOURCE VOUT 2 VIN SENSE
Together with a digital potentiometer and a Howland current
ADR43x RLW
pump, the ADR435 forms the reference source for a programmable
A1 V OP191 OUT
current as
V FORCE OUT 6 + RL
 R2 + A R2B 
GND
 
4
008  R1 I  = × (4) L W V   04500- R2B   Figure 37. Advantage of Kelvin Connection  
DUAL POLARITY REFERENCES
and Dual polarity references can easily be made with an operational D V = × (5) amplifier and a pair of resistors. To avoid defeating the accuracy W V N REF 2 obtained by the ADR43x, it is imperative to match the resistance where: tolerance as wel as the temperature coefficient of al the components. D is the decimal equivalent of the input code.
VIN
N is the number of bits.
1µF 0.1µF 2
In addition, R1' and R2' must be equal to R1 and (R2
V
A + R2B),
IN VOUT 6 +5V R1 R2
respectively. In theory, R2B can be made as small as needed to
ADR435 10kΩ 10kΩ U1
achieve the necessary current within the A2 output current
+10V
driving capability. In this example, the OP2177 can deliver a
GND TRIM 5 4 V+
maximum output current of 10 mA. Because the current pump
OP1177 –5V
employs both positive and negative feedback, C1 and C2
U2 V–
capacitors are needed to ensure that the negative feedback
R3 5kΩ
009 prevails and, therefore, avoids oscillation. This circuit also
–10V
04500- al ows bidirectional current flow if the VA and VB inputs of Figure 38. +5 V and −5 V References Using ADR435 the digital potentiometer are supplied with the dual polarity
+2.5V
references, as shown in Figure 40.
+10V C1 2 10pF VIN VOUT 6 VDD R1' R2' ADR435 R1 50kΩ 1kΩ U1 5.6kΩ 2 VDD V 5 GND TRIM IN TRIM 5 4 R2 ADR435 V+ 5.6kΩ V+ U1 U2 C2 OP2177 OP1177 AD5232 V V DD 10pF A2 OUT 6 U2 GND V– A R2B V– 4 –2.5V V+ R1 10Ω
010
50kΩ VSS B W –10V OP2177
04500-
A1 R2A
Figure 39. +2.5 V and −2.5 V References Using ADR435
V– 1kΩ + I VL L VSS –
011
IL
04500- Figure 40. Programmable Current Source Rev. M | Page 18 of 22 Document Outline Features Applications Pin Configurations General Description Table of Contents Revision History Specifications ADR430 Electrical Characteristics ADR431 Electrical Characteristics ADR433 Electrical Characteristics ADR434 Electrical Characteristics ADR435 Electrical Characteristics Absolute Maximum Ratings Thermal Resistance ESD Caution Typical Performance Characteristics Theory of Operation Basic Voltage Reference Connections Noise Performance High Frequency Noise Turn-On Time Applications Information Output Adjustment Reference for Converters in Optical Network Control Circuits High Voltage Floating Current Source Kelvin Connection Dual Polarity References Programmable Current Source Programmable DAC Reference Voltage Precision Voltage Reference for Data Converters Precision Boosted Output Regulator Outline Dimensions Ordering Guide