Datasheet ADA4500-2 (Analog Devices) - 21

link to page 21 link to page 21 link to page 16 link to page 16
ADA4500-2 Data Sheet
The ADA4500-2 solves the crossover distortion problem by using Figure 62 shows the elimination of the crossover distortion in an on-chip charge pump in its input structure to power the input the ADA4500-2. This solution improves the CMRR performance differential pair (see Figure 61). The charge pump creates a tremendously. For example, if the input varies from rail to rail supply voltage higher than the voltage of the supply, allowing on a 5 V supply rail, using a part with a CMRR of 70 dB minimum, the input stage to handle a wide range of input signal voltages an input-referred error of 1581 μV is introduced. The ADA4500-2, without using a second differential pair. With this solution, the with its high CMRR of 90 dB minimum (over its full operating input voltage can vary from one supply voltage to the other with temperature) reduces distortion to a maximum error of 158 μV no distortion, thereby restoring the full common-mode dynamic with a 5 V supply. The ADA4500-2 eliminates crossover distortion range of the op amp. without unnecessary circuitry complexity and increased cost.
VCP 300 ADA4500-2 BIAS6 240 VSY = 5.0V CHARGE PUMP 180 VDD VDD 120 BIAS5 60 V) (µ 0 VIN+ VIN– OS M1 M2 BIAS4 V –60 –120 –AV OUT –180 –240 BIAS3 –300
8
0 1 2 3 4 5
-10 7
VCM (V)
61 10 Figure 62. Charge Pump Design Eliminates Crossover Distortion 102
VSS VSS
17-
OVERLOAD RECOVERY
106 Figure 61. ADA4500-2 Input Structure When the output is driven to one of the supply rails, the Some charge pumps are designed to run in an open-loop ADA4500-2 is in an overload condition. The ADA4500-2 recovers configuration. Disadvantages of this design include: a large ripple quickly from the overload condition. Typical op amp recovery voltage on the output, no output regulation, slow start-up, and a times can be in the tens of microseconds. The ADA4500-2 typically large power-supply current ripple. The charge pump in this op recovers from an overload condition in 1 μs from the time the amp uses a feedback network that includes a controllable clock overload condition is removed until the output is active again. driver and a differential amplifier. This topology results in a low This is important in, for example, a feedback control system. The ripple voltage; a regulated output that is robust to line, load, and fast overload recovery of the ADA4500-2 greatly reduces loop process variations; a fast power-on startup; and lower ripple on delay and increases the response time of the control loop (see the power supply current.1 The charge pump ripple does not Figure 41 to Figure 44). show up on an oscilloscope; however, it can be seen at a high frequency on a spectrum analyzer. The charge pump clock speed adjusts between 3.5 MHz (when the supply voltage is 2.7 V) to 5 MHz (at VSY = 5 V). The noise and distortion are limited only by the input signal and the thermal or flicker noise. 1 Oto, D.H.; Dham, V.K.; Gudger, K.H.; Reitsma, M.J.; Gongwer, G.S.; Hu, Y.W.; Olund, J.F.; Jones, H.S.; Nieh, S.T.K.; "High-Voltage Regulation and Process Considerations for High-Density 5 V-Only E2PROM's," IEEE Journal of Solid-State Circuits, Vol. SC-18, No.5, pp.532-538, October 1983. Rev. B | Page 20 of 24 Document Outline FEATURES APPLICATIONS PIN CONFIGURATION GENERAL DESCRIPTION TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS VSY = 2.7 V ELECTRICAL CHARACTERISTICS VSY = 5.0 V ELECTRICAL CHARACTERISTICS ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE ESD CAUTION PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION RAIL-TO-RAIL OUTPUT RAIL-TO-RAIL INPUT (RRI) ZERO CROSS-OVER DISTORTION OVERLOAD RECOVERY POWER-ON CURRENT PROFILE APPLICATIONS INFORMATION RESISTANCE AND CAPACITANCE SENSOR CIRCUIT ADAPTIVE SINGLE-ENDED-TO-DIFFERENTIAL SIGNAL CONVERTER The Challenge The Solution OUTLINE DIMENSIONS ORDERING GUIDE