LMH6551 Datasheet, PDF (13/19 Pages) National Semiconductor (TI) – Differential, High Speed Op Amp

Application Section (Continued)
20133201
FIGURE 4. Split Supply Bypassing Capacitors
The LMH6551 requires supply bypassing capacitors as
shown in Figure 4 and Figure 5. 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 capaci-
tor 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 25kΩ. If a different output common mode
voltage is desired drive this pin with a clean, accurate volt-
age reference.
20133212
FIGURE 5. Single Supply Bypassing Capacitors
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