LMH6551MAX_NOPB Datasheet, PDF (13/28 Pages) Texas Instruments – LMH6551 Differential, High Speed Op Amp

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LMH6551
SNOSAK7C – FEBRUARY 2005 – REVISED MARCH 2013
500
50:
100:
TWISTED PAIR
250
+
a ^{2 V}PP
V_CM
-
250
GAIN = 2
2 V_PP
50:
500
Figure 28. Fully Differential Cable Driver
With up to 15 V_PP differential output voltage swing and 80 mA of linear drive current the LMH6551 makes an
excellent cable driver as shown in Figure 28. The LMH6551 is also suitable for driving differential cables from a
single ended source.
The LMH6551 requires supply bypassing capacitors as shown in Figure 29 and Figure 30. 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. The SMT capacitors should be connected directly to a ground plane. Thin traces or small vias will reduce
the effectiveness of bypass capacitors. Also shown in both figures is a capacitor from the V_CM pin to ground. The
V_CM pin is a high impedance input to a buffer which sets the output common mode voltage. Any noise on this
input is transferred directly to the output. Output common mode noise will result in loss of dynamic range,
degraded CMRR, degraded Balance and higher distortion. The V_CM pin should be bypassed even if the pin in not
used. There is an internal resistive divider on chip to set the output common mode voltage to the mid point of the
supply pins. The impedance looking into this pin is approximately 25 kΩ. If a different output common mode
voltage is desired drive this pin with a clean, accurate voltage reference.
10 PF
V⁺
0.01 PF
10 PF
V⁺
0.01 PF 0.01 PF
+
V_CM
-
0.1 PF
0.1 PF
10 PF
0.01 PF
V^-
Figure 29. Split Supply Bypassing Capacitors
+
V_CM
-
0.1 PF
Figure 30. Single Supply Bypassing Capacitors
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