Datasheet AD8615, AD8616, AD8618 (Analog Devices) - 11

link to page 11
Data Sheet AD8615/AD8616/AD8618 APPLICATIONS INFORMATION INPUT OVERVOLTAGE PROTECTION
This reduces the overshoot and minimizes ringing, which in turn improves the frequency response of the AD8615/AD8616/ If the voltage applied at either input exceeds the supplies, place AD8618. One simple technique for compensation is the snubber, external resistors in series with the inputs. The resistor values which consists of a simple RC network. With this circuit in place, can be determined by the equation output swing is maintained and the amplifier is stable at all gains. V  V IN SY  5 mA Figure 38 shows the implementation of the snubber, which RS reduces overshoot by more than 30% and eliminates ringing The extremely low input bias current allows the use of larger that can cause instability. Using the snubber does not recover resistors, which allows the user to apply higher voltages at the the loss of bandwidth incurred from a heavy capacitive load. inputs. The use of these resistors adds thermal noise, which
VS = ±2.5V
contributes to the overall output voltage noise of the amplifier.
AV = 1 CL = 500pF
For example, a 10 kΩ resistor has less than 13 nV/√Hz of
)
thermal noise and less than 10 nV of error voltage at room
IV /D
temperature.
V OUTPUT PHASE REVERSAL (100m GE A
The AD8615/AD8616/AD8618 are immune to phase inversion,
T L
a phenomenon that occurs when the voltage applied at the input of
VO
the amplifier exceeds the maximum input common mode. Phase reversal can cause permanent damage to the amplifier and can create lock ups in systems with feedback loops. 7 -03 48
VS = ±2.5V TIME (2µs/DIV)
46 0
VIN = 6V p-p A
Figure 37. Driving Heavy Capacitive Loads Without Compensation
V = 1 RL = 10kΩ ) IV /D VEE (2V GE + VOUT V V– IN LTA V+ VO – 200Ω 500pF – V 500pF
38
CC 200mV
0 8- 64 04 Figure 38. Snubber Network 36 0 8-
TIME (2ms/DIV)
64 04 Figure 36. No Phase Reversal
VS = ±2.5V AV = 1 R DRIVING CAPACITIVE LOADS S = 200Ω CS = 500pF ) CL = 500pF
Although the AD8615/AD8616/AD8618 are capable of driving
V /DI
capacitive loads of up to 500 pF without oscillating, a large amount
0mV
of overshoot is present when operating at frequencies above
(10
100 kHz. This is especially true when the amplifier is configured
GE A
in positive unity gain (worst case). When such large capacitive
T L
loads are required, the use of external compensation is highly
VO
recommended. 9 03 8-
TIME (10µs/DIV)
64 04 Figure 39. Driving Heavy Capacitive Loads Using the Snubber Network Rev. G | Page 11 of 20 Document Outline Features Applications General Description Pin Configuration Table of Contents Revision History Specifications Absolute Maximum Ratings Thermal Resistance ESD Caution Typical Performance Characteristics Applications Information Input Overvoltage Protection Output Phase Reversal Driving Capacitive Loads Overload Recovery Time D/A Conversion Low Noise Applications High Speed Photodiode Preamplifier Active Filters Power Dissipation Power Calculations for Varying or Unknown Loads Calculating Power by Measuring Ambient Temperature and Case Temperature Calculating Power by Measuring Supply Current Outline Dimensions Ordering Guide