LMH6657_16 Datasheet, PDF (18/35 Pages) Texas Instruments – 270-MHz Single Supply, Single and Dual Amplifiers

LMH6657, LMH6658
SNOSA35G – AUGUST 2002 – REVISED JULY 2015
Feature Description (continued)
18
R_L = 100:
16
A_V = +10, POS
14
A_V = +10, NEG
12
A_V = +1, POS
10 ^{AV = +6, POS}
8
6 ^AV ^{= +6, NEG}
A_V = +2, POS
4
2
A_V = +1, NEG
0
A_V = +2, NEG
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0
V_O (V_PP)
Figure 49. Output 20%-80% Transition vs. Output Voltage
Swing (Noninverting Gain)
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18
R_L = 100:
16
A_V = -10, NEG
14
12
10 ^{AV = -5, NEG}
8
6 ^AV ^{= -5, POS}
A_V = -10, POS
A_V = -1, POS
4
A_V = -1, NEG
2
0
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0
V_O (V_PP)
Figure 50. Output 20%-80% Transition vs. Output Voltage
Swing (Inverting Gain)
Beyond a gain of 5 or so, the LMH6657/6658 output transition would be limited by bandwidth. For example, with
a gain of 5, the −3dB BW would be around 30MHz corresponding to a rise time of about 12ns (10% - 90%).
Assuming a near linear transition, the 20%-80% transition time would be around 9ns which matches the
measured results as shown in Figure 49.
When the output is heavily loaded, output swing may be limited by current capability of the device. Refer to
Output Current Capability section for more details.
7.3 Device Functional Modes
7.3.1 Output Phase Reversal
This is a problem with some operational amplifiers. This effect is caused by phase reversal in the input stage due
to saturation of one or more of the transistors when the inputs exceed the normal expected range of voltages.
Some applications, such as servo control loops among others, are sensitive to this kind of behavior and would
need special safeguards to ensure proper functioning. The LMH6657 and LMH6658 is immune to output phase
reversal with input overload. With inputs exceeded, the LMH6657 and LMH6658 output will stay at the clamped
voltage from the supply rail. Exceeding the input supply voltages beyond the Absolute Maximum Ratings of the
device could however damage or otherwise adversely effect the reliability or life of the device.
18
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