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ALD2724E 데이터시트(PDF) 2 Page - Advanced Linear Devices |
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ALD2724E 데이터시트(HTML) 2 Page - Advanced Linear Devices |
2 / 10 page 2 Advanced Linear Devices ALD2724E/ALD2724 GENERAL DESCRIPTION (cont'd) an ultra-high input impedance voltage follower/buffer that allows input and output voltage swings from positive to negative supply voltages. This feature is intended to greatly simplify systems design and eliminate higher voltage power supplies in many applications. Each ALD2724E/ALD2724 operational amplifier features individual, user-programmable offset voltage trimming re- sulting in significantly enhanced total system performance and user flexibility. EPAD technology is an exclusive ALD design which has been refined for analog applications where precision voltage trimming is necessary to achieve a desired performance. It utilizes CMOS FETs as in-circuit elements for trimming of offset voltage bias characteristics with the aid of a personal computer under software control. Once programmed, the set parameters are stored indefinitely. EPAD offers the circuit designer a convenient and cost- effective trimming solution for achieving the very highest amplifier/system performance. FUNCTIONAL DESCRIPTION The ALD2724E/ALD2724 utilizes EPADs as in-circuit ele- ments for trimming of offset voltage bias characteristics. Each ALD2724E/ALD2724 operational amplifier has a pair of EPAD-based circuits connected such that one circuit is used to adjust VOS in one direction and the other circuit is used to adjust VOS in the other direction. While each of the basic EPAD device is a monotonically adjustable (offset voltage trimming) programmable device, the VOS of the ALD2724E can be adjusted many times in both directions. Once pro- grammed, the set VOS levels are stored permanently, even when the device power is removed. Functional Description of ALD2724E/ALD2724 The ALD2724E is pre-programmed at the factory under standard operating conditions for minimum equivalent input offset voltage. It also has a guaranteed offset voltage pro- gram range, which is ideal for applications that require electrical offset voltage programming. The ALD2724E is an operational amplifier that can be trimmed stand-alone, with user application-specific pro- gramming or in-system programming conditions. User appli- cation-specific circuit programming refers to a situation where the Total Input Offset Voltage of the ALD2724E can be trimmed with the actual intended operating conditions. Take the example of an application circuit that uses + 5V and -5V power supplies, an operational amplifier input biased at +1V, and an average operating temperature at +85 °C; the circuit can be wired up to these conditions within an environ- mental chamber with the ALD2724E inserted into a test socket while it is being electrically trimmed. Any error in VOS due to these bias conditions can be automatically zeroed out. The Total VOS error, VOST, is now limited only by the adjustable range and the stability of VOS, and the input noise voltage of the operational amplifier. This Total Input Offset Voltage now includes VOS, as VOS is traditionally specified; plus the VOS error contributions from PSRR, CMRR, TCVOS, and noise. Typically, VOST ranges approximately ±25µV for the ALD2724E. In-System Programming refers to the condition where the EPAD adjustment is made after the ALD2724E has been inserted into a circuit board. In this case, the circuit design must provide for the ALD2724E to operate in both normal mode and in programming mode. One of the benefits of in- system programming is that not only the ALD2724E offset voltage from operating bias conditions has been accounted for, any residual errors introduced by other circuit compo- nents, such as resistor or sensor induced voltage errors, can also be programmed and corrected. In this way, the “in- system” circuit output can be adjusted to a desired level eliminating need for another trimming function. The ALD2724 is pre-programmed at the factory under standard operating conditions for minimum equivalent input offset voltage. The ALD2724 offers similar programmable features as the ALD2724E, but with more limited offset voltage program range. It is intended for standard operational amplifier applications where little or no electrical programming by the user is necessary. USER PROGRAMMABLE VOS FEATURE Each ALD2724E/ALD2724 has four additional pins, compared to a conventional dual operational amplifier which has eight pins. These four additional pins are named VE1A, VE2A for op amp A and VE1B, VE2B for op amp B. Each of these pins VE1A, VE2A, VE1B, VE2B (represented by VExx) are connected to a separate, internal offset bias circuit. VExx pins have initial internal bias voltage values of approximately 1 to 2 Volts. The voltage on these pins can be programmed using the ALD E100 EPAD Programmer and the appropriate Adapter Module. The useful programming range of voltages on VExx pins are 1 Volt to 4 Volts. VExx pins are programming pins, used during electrical programming mode to inject charge into the internal EPADs. Increasing voltage on VE1A/VE1B decreases the offset voltage whereas increasing voltage on VE2A/VE2B in- creases the offset voltage of op amp A and op amp B, respectively. During programming, voltages on VExx pins are increased incrementally to program the offset voltage of the opera- tional amplifier to the desired VOS. Note that desired VOS can be any value within the offset voltage programmable ranges, and can be either equal zero, a positive value or a negative value. This VOS value can also be reprogrammed to a different value at a later time, provided that the useful VE1x or VE2x programming voltage range has not been exceeded. The injected charge is then permanently stored. After programming, VExx pins must be left open in order for these voltages to remain at the programmed levels. Internally, VE1 and VE2 are programmed and connected differentially. Temperature drift effects between the two internal offset bias circuits cancel each other and introduce less net temperature drift coefficient change than offset voltage trimming techniques such as offset adjustment with an external trimmer potentiometer. While programming, V+, VE1 and VE2 pins may be alter- nately pulsed with 12V (approximately) pulses generated by the EPAD Programmer. In-system programming requires the ALD2722E application circuit to accommodate these programming pulses. If needed, this requirement can be accomplished by adding resistors at certain appropriate circuit nodes. |
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