LMH6552MA NSC [National Semiconductor], LMH6552MA Datasheet - Page 15

• Manufacturer Part Number: LMH6552MA
• Description: 1 GHz Fully Differential Amplifier
• Manufacturer: NSC [National Semiconductor]

ADC+Amplifier combinations. The use of the LMH6552 to
drive an ADC is determined by the application and the desired
sampling process (Nyquist operation, sub-sampling or over-
sampling). See application note (AN-236) for more details on
the sampling processes and application note (AN-1393) for
details on 'Using High Speed Differential Amplifiers to Drive
ADC's'. For more information regarding a particular ADC, re-
fer to the particular ADC datasheet for details.
TABLE 2. DIFFERENTIAL INPUT ADC's COMPATIBLE
WITH LMH6552 DRIVER
Product Number
ADC1173
ADC1175
ADC08351
ADC1175-50
ADC08060
ADC08L060
ADC08100
ADC08200
ADC081000
ADC08D1000
ADC10321
ADC10D020
ADC10030
ADC10040
ADC10065
ADC10DL065
ADC10080
ADC11DL066
ADC11L066
ADC12010
ADC12020
ADC12040
ADC12D040
ADC12DL040
ADC12DL065
ADC12DL066
ADC12L063
CLC5957
ADC12L080
ADC12C170
ADC14L020
ADC14L040
ADC14155
Sampling
(MSPS)
1000
1000
Rate
Max
100
200
170
155
15
20
42
50
60
60
20
20
27
40
65
65
80
66
66
10
20
40
40
40
65
66
63
70
80
20
40
Resolution
10
10
10
10
10
10
10
11
11
12
12
12
12
12
12
12
12
12
12
12
14
14
14
8
8
8
8
8
8
8
8
8
8
Channels
SINGLE
SINGLE
SINGLE
SINGLE
SINGLE
SINGLE
SINGLE
SINGLE
SINGLE
SINGLE
SINGLE
SINGLE
SINGLE
SINGLE
SINGLE
SINGLE
SINGLE
SINGLE
SINGLE
SINGLE
SINGLE
SINGLE
SINGLE
SINGLE
DUAL
DUAL
DUAL
DUAL
DUAL
DUAL
DUAL
DUAL
DUAL
15
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
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 15 V
of linear drive current the LMH6552 makes an excellent cable
driver as shown in Figure 9. The LMH6552 is also suitable for
driving differential cables from a single ended source.
POWER SUPPLY BYPASSING
The LMH6552 requires supply bypassing capacitors as
shown in Figure 10 and Figure 11. The 0.01 µF and 0.1 µF
capacitors 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.
A small capacitor, ~0.01 µF, placed across the supply rails,
and as close to the chip's supply pins as possible, can further
improve HD2 performance. Thin traces or small vias will re-
duce the effectiveness of bypass capacitors. Also shown in
both figures is a capacitor from the V
ground. These inputs are high impedance and can provide a
coupling path into the amplifier for external noise sources,
possibly resulting in loss of dynamic range, degraded CMRR,
degraded balance and higher distortion.
FIGURE 9. Fully Differential Cable Driver
PP
differential output voltage swing and 80 mA
OUT
CM
vs. Capacitive Load
and ENABLE pins to
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