Dual SPST-NC analog switch for precision signal routing
The MAX321CSA+ from Maxim Integrated is a dual-channel SPST-NC (normally-closed) analog switch in an 8-SOIC surface-mount package. It routes analog or digital signals with a maximum on-resistance of 35 Ohm and channel-to-channel matching of 300 mOhm, keeping gain errors tight across both channels. Switching is fast — 150 ns turn-on, 100 ns turn-off — so it handles sample-and-hold front ends and audio muting without missing edges. The normally-closed configuration means the signal path stays connected when the control voltage is low, a useful fail-safe for preamp inputs or reference lines that should not float on power loss.
Supply and signal range — what ±2.7 V to ±8 V buys you
The dual-supply range is ±2.7 V to ±8 V. With a 1:1 multiplexer/demultiplexer circuit, each switch passes signals rail-to-rail. Charge injection is 2 pC. Off-leakage maxes at 100 pA.
Crosstalk and channel isolation at 1 MHz
Channel-to-channel crosstalk is rated at -85 dB at 1 MHz. In a dual-switch package, that isolation keeps a signal on one channel from bleeding into the other — important when switching separate audio left/right paths or when one channel carries a precision reference while the other handles a dynamic signal. Off-channel capacitance is 9 pF per channel, so the isolation holds up into the low-MHz region.
Package and temperature grade
The 8-SOIC (0.154", 3.90 mm width) footprint is a standard analog-switch package — no surprises for layout reuse. The operating temperature range is 0°C to 70°C, commercial grade. That limits this part to indoor, controlled environments: benchtop instruments, audio gear, telecom line cards, and general-purpose industrial control panels that stay above freezing. Not rated for under-hood automotive or outdoor telecom cabinets without climate control.