LMH6657_16 Datasheet, PDF (19/35 Pages) Texas Instruments – 270-MHz Single Supply, Single and Dual Amplifiers

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8 Application and Implementation
LMH6657, LMH6658
SNOSA35G – AUGUST 2002 – REVISED JULY 2015
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
8.1.1 Output Characteristics
8.1.1.1 Output Current Capability
The LMH6657/6658 output swing for a given load can be determined by referring to the Output Voltage vs.
Output Current plots in Typical Characteristics. Characteristic Tables show the output current when the output is
1V from either rail. The plots and table values can be used to predict closed loop continuous value of current for
a given load. If left unchecked, the output current capability of the LMH6657 and LMH6658 could easily result in
junction temperature exceeding the maximum allowed value specified under Absolute Maximum Ratings. Proper
heat sinking or other precautions are required if conditions as such exist.
Under transient conditions, such as when the input voltage makes a large transition and the output has not had
time to reach its final value, the device can deliver output currents in excess of the typical plots mentioned above.
Plots shown in Figure 51 and Figure 52 depict how the output current capability improves under higher input
overdrive voltages:
10
V_S = ±5V
25°C
10
V_S = ±5V
25°C
1 20mV
500mV
1 ^-20mV
-500mV
0.1
0
50
100
150
200
I_OUT (mA)
Figure 51. V_OUT vs. I_SOURCE (for Various Overdrive)
0.1
0
50
100 150 200 250
I_OUT (mA)
Figure 52. V_OUT vs. I_SINK (for Various Overdrive)
The LMH6657 and LMH6658 output stage is designed to swing within approximately one diode drop of each
supply voltage by utilizing specially designed high speed output clamps. This allows adequate output voltage
swing even with 5-V supplies and yet avoids some of the issues associated with rail-to-rail output operational
amplifiers. Some of these issues are:
• Supply current increases when output reaches saturation at or near the supply rails
• Prolonged recovery when output approaches the rails
The LMH6657 and LMH6658 output is exceedingly well-behaved when it comes to recovering from an overload
condition. As can be seen from Figure 53, the LMH6657 and LMH6658 will typically recover from an output
overload condition in about 18 ns, regardless of the duration of the overload.
Copyright © 2002–2015, Texas Instruments Incorporated
Product Folder Links: LMH6657 LMH6658
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