Attention to good layout practices is always recommended. For best operational performance of the device, use good printed circuit board (PCB) layout practices:

• To avoid converting common-mode signals into differential signals and thermal electromotive forces (EMFs), make sure that both input paths are symmetrical and well-matched for source impedance and capacitance.
• As shown in Figure 9-14, keep the external gain resistor close to the RG pins to keep the loop inductance as low as possible and to avoid a potential parasitic coupling path. Even slight mismatch in parasitic capacitance at the gain setting pins can degrade CMRR over frequency. In applications that implement gain switching using switches or PhotoMOS® relays to change the value of R_G, select the component so that the switch capacitance is as small as possible, and most importantly, so that capacitance mismatch between the RG pins is minimized.
• Noise can propagate into analog circuitry through the power pins of the device and of the circuit as a whole. Bypass capacitors reduce the coupled noise by providing low-impedance power sources local to the analog circuitry.
  • Connect low-ESR, 0.1-µF ceramic bypass capacitors between each supply pin and ground, placed as close as possible to the device. A single bypass capacitor from V+ to ground is applicable for single-supply applications.
• To reduce parasitic coupling, run the input traces as far away as possible from the supply or output traces. If these traces cannot be kept separate, crossing the sensitive trace perpendicular to the noisy trace is much better than in parallel.
• Leakage on the FDA_IN+ and FDA_IN– pins can cause in a dc offset error in the output voltages. Additionally, excessive parasitic capacitance at these pins can result in decreased phase margin and affect the stability of the output stage. If these pins are not used to implement deliberate capacitive feedback, follow best practices to minimize leakage and parasitic capacitance. Consider implementing keep-out areas in any ground planes that lie immediately below the pins.
• Minimize the number of thermal junctions. Ideally, the signal path is routed within a single layer without vias.
• Keep sufficient distance from major thermal energy sources (circuits with high power dissipation). If not possible, place the device so that the effects of the thermal energy source on the high and low sides of the differential signal path are evenly matched.
• Solder the thermal pad to the PCB. For the INA851 to properly dissipate heat, connect the thermal pad to a plane or large copper pour that is electrically connected to VS–, even for low-power applications.
• Keep the traces as short as possible.