Dual SPST switch with 35 Ohm on-resistance
The MAX320CSA+ is a dual single-pole single-throw (SPST) normally-open analog switch from Analog Devices, packaged in an 8-SOIC. Each switch presents a maximum 35 Ohm on-resistance, with channel-to-channel matching held to 300 mOhm — the resistance mismatch between the two channels stays under a third of an ohm, which matters when the switch pair carries a differential signal where gain matching depends on the series resistance. Switching is specified at 150 ns turn-on and 100 ns turn-off maximum. For a multiplexed data-acquisition front-end scanning at 500 kHz, the 150 ns settling window sets the minimum sample period before the downstream ADC starts conversion.
Signal integrity: crosstalk, charge injection, leakage
Crosstalk between channels is rated at -85 dB at 1 MHz. In a precision analog multiplexer switching a 10 Vpp signal, -85 dB means the coupled noise on the off channel is roughly 560 µV — below the LSB of a 16-bit ADC with a 5 V reference, so the adjacent channel bleed does not limit the system resolution at that frequency. Charge injection is 2 pC typical. When the switch opens, the 2 pC charge dumped onto the hold capacitor in a sample-and-hold stage produces a voltage step of 2 pC / C_hold — for a 10 nF hold cap that is 200 µV, a known error term that the downstream ADC's acquisition time must absorb before conversion starts. Maximum off-channel leakage current is 100 pA. In a high-impedance sensor front-end with a 10 MOhm source, 100 pA leakage develops 1 mV of offset error — negligible for a 12-bit system but worth budgeting in a 24-bit precision path where the leakage floor competes with the sensor's own bias current. Each channel's off-capacitance is 9 pF on both source and drain sides. The 9 pF CS(off) and CD(off) set the AC feedthrough floor — at 1 MHz the capacitive coupling through the open switch is roughly 1/(2π × 9 pF × 1 MHz) ≈ 18 kOhm, which in a 10 kOhm load creates a measurable signal bleed that the crosstalk spec already captures.
The switch operates from a dual supply of ±2.7 V to ±8 V. With a ±5 V rail the analog signal swing reaches ±4.5 V before hitting the supply headroom — the 35 Ohm Ron is specified at that supply condition and increases as the supply drops toward ±2.7 V. Temperature range is 0°C to 70°C ambient — commercial grade. The switch is specified for indoor bench equipment, lab instrumentation, and telecom line cards where the enclosure stays climate-controlled. No industrial or automotive temperature coverage on this variant.
Package and board integration
Housed in an 8-SOIC (0.154-inch body width, 3.90 mm width) surface-mount package, supplied in Tube. The footprint matches the industry-standard SOIC-8 land pattern — no special pad geometry required.