LMH6657 Datasheet, PDF (16/29 Pages) National Semiconductor (TI) – 270MHz Single Supply, Single & Dual Amplifiers

LMH6657, LMH6658
SNOSA35F – AUGUST 2002 – REVISED MARCH 2013
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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 51. Output 20%-80% Transition vs. Output Voltage Swing (Non-Inverting Gain)
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 52. 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 51.
When the output is heavily loaded, output swing may be limited by current capability of the device. Refer to
Output Current Capability section, below, for more details.
Output Characteristics
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 (Typical Performance Characteristics section). 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 LMH6657/6658 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 53 and 54 below depict how the output current capability improves under higher input
overdrive voltages:
16
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