HT54123ARZ from HTCSEMI, in a SOP-8. 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	VR	input	Reference/negative differential amplifier input. Connected to the ZCT (Zero Current Transformer) secondary side (typically through resistor RL) and to the internal reference voltage generator via the feedback network. Sets the trip threshold together with VI.
2	VI	input	Signal/positive differential amplifier input from the ZCT secondary coil. Compared against VR by the internal differential amplifier (gain ~1000) to detect earth leakage current.
3	GND	power_in	Ground / negative supply return for the IC. Reference for VCC and all internal bias.
4	OD	output	Differential amplifier output. Provides the amplified ZCT signal; an external capacitor (C2, ~0.047 µF between OD and NR) is connected here to integrate the amplifier output. Typical IO(D) ~20 µA (VR-VI=30 mV, VOD=1.2 V).
5	SC	output	SCR gate drive output. Sources a ~0.4 mA output pulse (typ. 400 µA, up to 800 µA) to trigger the external SCR gate when the latch is activated, energizing the trip coil that opens the circuit breaker.
6	NR	passive	Noise-reduction / integration node. External capacitor to ground (typ. 0.047 µF C2) sets the integration time constant of the amplified signal to obtain adequate trip delay per KSC4613. A capacitor between pin 6 and pin 7 (~0.047 µF) may also be added when noise is high.
7	OS	output	Level comparator / latch output. Presents the pulse signal after the internal latch circuit; used with an external capacitor (C3, ~0.047 µF) and drives (through the latch) the SC output that fires the SCR. Latch-on voltage typ. 1.0 V.
8	VCC	power_in	Positive supply pin, powered directly from the rectified AC line via series resistor RS and capacitor CS. Operating range 12-20 V (abs. max 20 V, ICC max 8 mA); internal Zener protection and voltage regulator provide the bias voltage. Typical ICC ~400 µA at VCC=12 V.

Key specifications

Parameter	Value
Manufacturer	HTCSEMI
Package	SOP-8
Category	Op-amp/Cmp
Pins	8

Ordering variants

Same part, different packaging or reel option.

HT54123ARZ
HT54123ARZSOP
HT54123ARZR
HT54123ARZDIP

CAD (KiCad official)

Symbol: HT54123ARZ
Footprint: Package_SO:SOIC-8_3.9x4.9mm_P1.27mm
3D model: SOP-8 (KiCad packages3D, STEP)

Provenance

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

Datasheet: HTCSEMI datasheet (10 pp, sha256 7feefbbddc0101ef, 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