RE46C191S16TF from Microchip Tech, in a SOIC-16. Pinout and pin descriptions extracted from the manufacturer datasheet by ds2sf; symbol, footprint, and 3D from KiCad-official CAD.

Pinout

Pin	Name	Type	Function
1	VSS	power_in	Negative supply voltage (0 V / battery negative). All internal ground reference; C1 bulk capacitor should be located closest to this pin.
2	IRED	output	Provides a regulated, programmable pulsed current sink for the infrared emitter diode. Programmable levels 50/100/150/200 mA typical (IIRED = 45-220 mA range) with 100-400 us on-time.
3	VDD	power_in	Positive supply / battery voltage input. Operating range 2.0-5.0 V (absolute max 5.5 V); typical two-AA battery application. C2 decoupling capacitor must be located as close as possible to this pin.
4	TEST	input	Digital input used to invoke Test modes and the nine-minute Timer/Hush mode (push-to-test / hush button). Has an internal pull-down (IPD1 typ 10 uA). VIH >= 6.2 V (VBST = 9V), VIL <= 2.7 V. Absolute VIN range -0.3 V to VDD + 0.3 V.
5	TEST2	input	Test input used for Test and Programming modes (EEPROM calibration/parametric programming). Has an internal pull-down (IPD1 typ 10 uA). Absolute VIN range -0.3 V to VDD + 0.3 V.
6	IRP	input	Photo diode anode connection to the internal photo integrator/amplifier. Input leakage +/-200 pA over VDD-VSS.
7	IRN	input	Photo diode cathode connection to the internal photo integrator/amplifier. Input leakage +/-200 pA over VDD-VSS.
8	RLED	output	Open-drain NMOS output to drive a visible (red) LED. Sinks load current for the low-battery test and provides visual indication for Alarm and Hush modes. VOL2 <= 300 mV at IOL = 10 mA, VBST = 9 V.
9	GLED	output	Open-drain NMOS output to drive a visible (green) LED providing visual indication of an Alarm Memory condition. VOL3 <= 300 mV at IOL = 10 mA, VBST = 3.6 V.
10	FEED	input	Feedback electrode input from the DC-DC boost converter divider through a current-limiting resistor (used to sense VBST). Absolute VIN range -10 V to +22 V. If unused, this pin must be connected to VDD or VSS.
11	IRCAP	passive	Connection for the IRED reservoir capacitor. Charged from VBST during smoke check; IIRCAP typ 500 uA. IRCAP turn-on/off thresholds 4.0 V / 4.4 V typical (VBST = 5 V).
12	IO	bidirectional	Bidirectional interconnect I/O for daisy-chaining multiple detectors (up to 40 units so any unit's alarm signals all others). Includes internal pull-down and charge-dump device (~1.3 s post-alarm). Active-high alarm signal driven from boosted rail; VIH2 >= 2.0 V, VIL2 <= 0.8 V.
13	HB	output	Piezoelectric horn driver output connected to the metal electrode of the transducer. Push-pull driver; VOL1 <= 500 mV / VOH1 >= 8.5 V at IOL = 16 mA, VBST = 9 V. Driven complementary to HS to produce a bridged waveform.
14	HS	output	Piezoelectric horn driver complementary output to HB, connected to the ceramic electrode of the transducer. Same drive levels as HB (VOL <= 500 mV, VOH >= 8.5 V at 16 mA, VBST = 9 V).
15	VBST	power_out	Boosted voltage produced by the internal DC-DC converter (feedback set by external divider on FEED). Nominal VBST1 ~3.6 V (smoke-check / GLED) and VBST2 ~9.6 V (horn/RLED). Absolute max 13 V. Requires an external inductor (LX pin), Schottky diode and reservoir capacitor.
16	LX	output	Open-drain NMOS switch output that drives the boost-converter inductor. The inductor connects between LX and VDD; provides a low-resistance path to VSS during the switch on-phase. Absolute VLX -0.3 V to 13 V; can source current pulses > 1 A in High Boost mode.

Key specifications

Parameter	Value
Manufacturer	Microchip Tech
Package	SOIC-16
Category	Optoisolators
Pins	16

Ordering variants

Same part, different packaging or reel option.

RE46C191S16TFS16F
RE46C191S16TF
RE46C191S16TFSS20
RE46C191S16TFSS20T

CAD (KiCad official)

Symbol: RE46C191S16TF
Footprint: Package_SO:SOIC-16_3.9x9.9mm_P1.27mm
3D model: SOIC-16 (KiCad packages3D, STEP)

Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

Datasheet: Microchip Tech datasheet (48 pp, sha256 c8476c22f235f9ff, retrieved 2026-08-17, tier: lcsc)
Extractor: ds2sf (Claude). Every pin and dimension is cited to a datasheet page; it refuses to fabricate.
CAD: KiCad official libraries (CC-BY-SA 4.0).

Datasheet PDF