UC3842-TD from TDSEMIC, 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	COMP	output	Error amplifier output. Used for external loop compensation via an RC network between COMP and VFB (pin 2).
2	VFB	input	Inverting input of the internal error amplifier. Normally connected via a resistor divider from the regulated switching-supply output; compared against the internal 2.5 V reference on the non-inverting input.
3	ISENSE	input	Current-sense input. Voltage proportional to primary-side switch current (across a sense resistor Rs) is applied here. PWM latch resets when this input exceeds the internal 1 V threshold, providing cycle-by-cycle current limiting.
4	RT/CT	passive	Oscillator timing pin. Connect RT from VREF (pin 8) to this pin and CT from this pin to GND to set the oscillator frequency and maximum duty cycle. Maximum operating frequency 500 kHz.
5	GND	power_in	Signal and power ground return for the IC.
6	OUTPUT	output	Totem-pole gate driver output for the external power MOSFET. Capable of sourcing/sinking peak currents up to 1 A. Internally clamped by a 22 V zener.
7	VCC	power_in	Positive supply for the control IC. UVLO turn-on at ~16 V (typ) and turn-off at ~10 V (typ) with ~29 V internal zener clamp. Absolute maximum 30 V. Startup current < 0.5 mA (Ist ≤ 0.3 mA at Vi=14 V).
8	VREF	power_out	5 V (±2%) trimmed bandgap reference output. Sources up to ~30 mA (Isc typ -100 mA). Typically feeds the oscillator timing resistor RT to charge CT on pin 4.

Key specifications

Parameter	Value
Manufacturer	TDSEMIC
Package	SOP-8
Category	PMIC
Pins	8

Ordering variants

Same part, different packaging or reel option.

UC3842-TDM/TR
UC3842-TDN

CAD (KiCad official)

Symbol: UC3842-TD
Footprint: Package_SO:SOIC-8_3.9x4.9mm_P1.27mm
3D model: SOP-8 (KiCad packages3D, STEP)

3D model downloads

Two STEP files. Same geometry, different body top:

File	Size	Use it when
`uc3842-td.step`	122 KB	You want the bare part, or you mark your own boards.
`uc3842-td-etched.step`	2.0 MB	You want the part with `UC3842-TD` already on it.

The marking in the etched file is real recessed geometry cut into the solid, not a texture or a decal: 486 faces against 147 in the bare model. It survives export, section views, and rendering in any CAD tool, and it drops straight into KiCad or Fusion with no extra setup.

Provenance

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

Datasheet: TDSEMIC datasheet (9 pp, sha256 350281e75156b241, retrieved 2026-08-17, tier: lcsc)
Datasheet language: Chinese. Pin names, descriptions, and specs on this page were extracted and translated to English by ds2sf; the linked PDF is the manufacturer original.
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