TD1688 from Techcode Semicon, in a ESOP-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	SW	output	Power switching output; drain of the internal N-channel power MOSFET (RDS(ON) ≈ 0.7Ω). Connects to the external inductor and Schottky freewheeling diode to supply the output LC filter. Switches between VIN and near-GND at 480 kHz.
2	EN	input	On/Off enable input. Pull above VEN_R ≈ 1.35V (falling threshold ≈ 1.17V, hysteresis ≈ 180mV) to turn the device on. For automatic enable, connect to VIN through a 1MΩ resistor. Absolute max 6V.
3	NC	unconnected	Not connected. Leave floating or tie to ground; no internal bond.
4	FB	input	Feedback input to the internal error amplifier. Regulates to a 0.812V bandgap reference (0.792-0.832V). Connect to the tap of an external resistor divider from VOUT to GND. Frequency-foldback engages when FB < 300mV to limit short-circuit current.
5	GND	power_in	Signal/analog ground and voltage reference for the regulated output. Isolate this node from the D1-to-C1 high-current ground path to prevent switching current spikes from being induced into the sensitive analog reference.
6	NC	unconnected	Not connected. Leave floating or tie to ground; no internal bond.
7	VIN	power_in	Supply voltage input. Operates from 11V to 60V unregulated input (absolute max 60V). Requires a local bypass capacitor (C1, typ. 1µF ceramic X5R/X7R) to prevent large voltage spikes at the input.
8	BST	passive	Bootstrap capacitor node for the high-side gate driver. Connect a 0.1µF capacitor between SW and BST to form a floating supply that drives the power switch gate above VIN. Absolute max VBST = VSW-0.3 to VSW+6V.
9	GND	power_in	Exposed thermal pad. Electrically GND. Connect to the system ground plane with a large copper area for good thermal conductivity and low-impedance return; critical for maintaining junction temperature within limits (θJA ≈ 50°C/W).

Key specifications

Parameter	Value
Manufacturer	Techcode Semicon
Package	ESOP-8
Category	PMIC
Pins	9

Ordering variants

Same part, different packaging or reel option.

TD1688M
TD1688MR

CAD (KiCad official)

Symbol: TD1688
Footprint: Package_SO:SOIC-8-1EP_3.9x4.9mm_P1.27mm_EP2.41x3.3mm
3D model: ESOP-8 (KiCad packages3D, STEP)

3D model downloads

Two STEP files. Same geometry, different body top:

File	Size	Use it when
`td1688.step`	193 KB	You want the bare part, or you mark your own boards.
`td1688-etched.step`	1.3 MB	You want the part with `TD1688` already on it.

The marking in the etched file is real recessed geometry cut into the solid, not a texture or a decal: 331 faces against 63 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: Techcode Semicon datasheet (8 pp, sha256 4efdec95ca3aa43f, 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