LMH6554LEE/NOPB National Semiconductor, LMH6554LEE/NOPB Datasheet - Page 13

• Manufacturer Part Number: LMH6554LEE/NOPB
• Description: IC OP AMP DIFF 2.8GHZ 14LLP
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LMH6554LEE/NOPB

• Amplifier Type: Differential
• Number Of Circuits: 1
• Output Type: Differential
• Slew Rate: 6200 V/µs
• -3db Bandwidth: 2.8GHz
• Current - Input Bias: 1µA
• Voltage - Input Offset: 6500µV
• Current - Supply: 52mA
• Current - Output / Channel: 150mA
• Voltage - Supply, Single/dual (±): 4.7 V ~ 5.25 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 14-LLP
• No. Of Amplifiers: 1
• Input Offset Voltage: 3mV
• Bandwidth: 2.8GHz
• Supply Voltage Range: 4.7V To 5.25V
• Supply Current: 52mA
• Amplifier Case Style: LLP
• No. Of Pins: 14
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Gain Bandwidth Product: -
• Other names: LMH6554LEETR

Output Noise Performance and
Measurement
Unlike differential amplifiers based on voltage feedback ar-
chitectures, noise sources internal to the LMH6554 refer to
the inputs largely as current sources, hence the low input re-
ferred voltage noise and relatively higher input referred cur-
rent noise. The output noise is therefore more strongly
coupled to the value of the feedback resistor and not to the
closed loop gain, as would be the case with a voltage feed-
back differential amplifier. This allows operation of the
LMH6554 at much higher gain without incurring a substantial
noise performance penalty, simply by choosing a suitable
feedback resistor.
Figure 6
figure for the LMH6554 in a 50Ω system. A feedback resistor
value of 200Ω is chosen for the LLP package to minimize
output noise while simultaneously allowing both high gain (7
V/V) and proper 50Ω input termination. Refer to the section
titled Single Ended Input Operation for calculation of resistor
and gain values. Noise figure values at various frequencies
are shown in the plot titled Noise Figure in the Typical Per-
formance Characteristics section.
Driving Capacitive Loads
As noted previously, capacitive loads should be isolated from
the amplifier output with small valued resistors. This is par-
ticularly the case when the load has a resistive component
that is 500Ω or higher. A typical ADC has capacitive compo-
nents of around 10 pF and the resistive component could be
1000Ω or higher. If driving a transmission line, such as 50Ω
FIGURE 6. Noise Figure Circuit Configuration
FIGURE 5. Driving a 10-bit Gigasample ADC
shows a circuit configuration used to measure noise
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coaxial or 100Ω twisted pair, using matching resistors will be
sufficient to isolate any subsequent capacitance. For other
applications see the Suggested R
charts in the Typical Performance Characteristics section.
Balanced Cable Driver
With up to 5.68 V
LMH6554 can be configured as a cable driver. The LMH6554
is also suitable for driving differential cables from a single
ended source as shown in
Power Supply Bypassing
The LMH6554 requires supply bypassing capacitors as
shown in
pacitors should be leadless SMT ceramic capacitors and
should be no more than 3 mm from the supply pins. These
capacitors should be star routed with a dedicated ground re-
turn plane or trace for best harmonic distortion performance.
Thin traces or small vias will reduce the effectiveness of by-
pass capacitors. Also shown in both figures is a capacitor from
the VCM and V
impedance and can provide a coupling path into the amplifier
for external noise sources, possibly resulting in loss of dy-
namic range, degraded CMRR, degraded balance and higher
distortion.
FIGURE 8. Split Supply Bypassing Capacitors
FIGURE 7. Fully Differential Cable Driver
Figure 8
EN
and
PP
pins to ground. These inputs are high
differential output voltage swing the
Figure
Figure
9. The 0.01 μF and 0.1 μF ca-
7.
OUT
vs. Capacitive Load
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