A TSSOP-28 package carries 28 gull-wing leads on a 9.7 mm × 4.4 mm plastic body that stands no taller than 1.2 mm, with the leads on a 0.65 mm pitch. It is registered to JEDEC outline MO-153 (variation AE) and mounts on a two-row surface-mount land about 5.8 mm across. This guide gives the exact dimensions, the pin-numbering rule with a real pinout, a verified footprint, and the thermal and sourcing trade-offs that decide whether the TSSOP-28 package belongs in your design.

Key takeaways

• Body: 9.6–9.8 mm long × 4.3–4.5 mm wide, ≤ 1.2 mm tall, 0.65 mm lead pitch, 14 leads per side (MPS drawing MF-PO-D-0024, JEDEC MO-153 variation AE).
• Footprint: 28 pads, 1.60 mm × 0.40 mm, on 0.65 mm pitch, 5.80 mm span between rows (MPS recommended land).
• Same width as TSSOP-24: the 4.4 mm body, 6.4 mm lead span, 0.65 mm pitch and 1.2 mm height are shared; only the length grows, from 7.8 mm to 9.7 mm.
• Thermal: a plain leaded TSSOP runs near 100 °C/W junction-to-ambient; the exposed-pad (HTSSOP) version drops that to the mid-20s to mid-30s °C/W when its pad is soldered to copper (TI TLC5940, DRV8952 datasheets).
• Handling: the standard part is MSL 1; the exposed-pad HTSSOP version is MSL 2 and needs a dry-pack regime (TI addendums for MSP430G2553IPW28 and TLC5940PWP).

What “TSSOP-28” actually specifies

TSSOP stands for Thin Shrink Small Outline Package. The “28” is the lead count: 14 gull-wing leads down each long side. The family comes in three body widths — 3.0 mm, 6.1 mm, and the 4.4 mm width used by the 28-lead part — with a standard 0.65 mm pitch (a denser 0.5 mm pitch exists on some variants). The whole family is registered to JEDEC MO-153; the 28-lead 4.4 mm-body member is variation AE. Against an SOIC of the same lead count it is thinner and finer-pitch, which is the point: a sub-1.2 mm mounted height in far less board area.

One thing catches sourcing engineers out. The same physical outline ships under many vendor codes. Texas Instruments calls it PW, and PWP for the exposed-pad PowerPAD version; NXP registers it as SOT361-2; Analog Devices uses RU; ST lists it as TSSOP28 or HTSSOP-28. So “TSSOP-28” names an outline, not one drawing. Match the specific vendor drawing to the exact part number before you build the library part.

TSSOP-28 dimensions

A TSSOP-28 package measures 9.6–9.8 mm long and 4.3–4.5 mm wide, stands 1.2 mm tall at most, and spaces its 28 leads on a 0.65 mm pitch, with a lead span of 6.2–6.6 mm across the tips. Those four numbers — body, height, pitch, span — are what you place and route to.

The full mechanical set below is from Monolithic Power’s outline drawing MF-PO-D-0024, which conforms to JEDEC MO-153 variation AE; NXP’s SOT361-2 gives the same 4.4 mm × 9.7 mm × 0.95 mm body. All values in millimetres.

Feature	Symbol	Min	Max
Body length	D	9.60	9.80
Body width	E1	4.30	4.50
Lead span (tip to tip)	E	6.20	6.60
Overall height	A	—	1.20
Standoff height	A1	0.05	0.15
Lead pitch	e	0.65 (basic)	—
Lead width	b	0.19	0.30
Lead thickness	c	0.09	0.20
Lead-foot length	L	0.45	0.75
Lead-foot angle	θ	0°	8°

The relationship to the 24-lead part is worth holding in mind: the body width (4.4 mm), lead span (6.4 mm nominal), height (1.2 mm max) and 0.65 mm pitch are identical. Adding four leads only lengthens the body, from 7.8 mm to 9.7 mm. If you already have a TSSOP-24 footprint, the TSSOP-28 land is the same pad on the same pitch, extended by two more pads per side.

Exposed-pad members (HTSSOP, TSSOP-EP), registered as MO-153 variation AET, add a metal pad on the underside for heat removal. The body and leads track the standard part; the pad changes the footprint and the thermal behaviour, both covered below.

TSSOP-28 pinout and pin numbering

Pin numbering is a package convention, not a per-device property. Hold the part with its marked face up: pin 1 is the lead nearest the pin-1 identifier — a dot or bevelled corner — at one end. Numbering increases down that side to pin 14, jumps to pin 15 on the diagonally opposite corner, and increases back up to pin 28. Counter-clockwise, always.

What each pin does is entirely part-specific — the package fixes only geometry and numbering. As a concrete map, here is TI’s MSP430G2553 microcontroller in the 28-lead TSSOP (PW), from its datasheet, viewed from the top (primary port names shown):

Pin	Left side	Right side	Pin
1	DVCC	DVSS	28
2	P1.0	XIN / P2.6	27
3	P1.1	XOUT / P2.7	26
4	P1.2	TEST / SBWTCK	25
5	P1.3	RST / NMI / SBWTDIO	24
6	P1.4	P1.7	23
7	P1.5	P1.6	22
8	P3.1	P3.7	21
9	P3.0	P3.6	20
10	P2.0	P3.5	19
11	P2.1	P2.5	18
12	P2.2	P2.4	17
13	P3.2	P2.3	16
14	P3.3	P3.4	15

Power sits at the corners here — DVCC on pin 1, DVSS on pin 28 — with the reset and JTAG/Spy-Bi-Wire cluster (RST, TEST, XOUT, XIN) grouped at the top of the right side. Swap in a different 28-lead part, such as TI’s TLC5940 LED driver, and the pin geometry is identical while the signal names change completely; the TLC5940 runs its 16 outputs OUT0–OUT15 down and around from pin 7.

TSSOP-28 land pattern (footprint)

The recommended land pattern for a TSSOP-28 places 28 pads, each 1.60 mm long × 0.40 mm wide, on the 0.65 mm pitch, with a 5.80 mm span between the two rows (Monolithic Power MF-PO-D-0024). That 5.80 mm span is set by the lead geometry, not the body, so it is the same as a TSSOP-24 land; you simply add two pads per side.

Choose the density by process. That MPS land sits at roughly the IPC-7351 Nominal (Density Level B) point, which fits a general reflow line. If the board sees hand-rework or you want inspectable toe fillets, generate the Level A (Most) land with longer toes. Reserve Level C (Least) for fine-pitch reflow backed by automated optical inspection. Most CAD libraries generate all three from the IPC-7351 rules; pick the level to match your assembly, not the tightest one available.

On stencils, a 0.125 mm foil with a 1:1 aperture on the signal pads is a sound default. For the exposed-pad HTSSOP-28, do not flood the thermal pad: window the paste to roughly 70–80% coverage and add tented or plugged vias down to an inner plane, or the part will float and the joint will void.

Standard vs exposed-pad: the thermal decision

Heat is the main reason to think twice about a plain TSSOP-28. A standard leaded TSSOP in this family sits near 100 °C/W junction-to-ambient on a JEDEC board — the 24-lead TCA9548A measures 108.8 °C/W in the same PW outline, and the longer 28-lead body improves that only slightly, because heat still leaves mainly through the leads. That is fine for logic, interface and low-power MCU parts, and tight for anything dissipating hundreds of milliwatts.

Adding an exposed pad rewrites the number. Measured junction-to-ambient for two exposed-pad 28-pin HTSSOP parts on a JEDEC board:

Device (28-pin HTSSOP, exposed pad)	RθJA	Notes
TI TLC5940 (PWP)	36.7 °C/W	RθJC(bot) 2.3 °C/W, ψJT 0.6 °C/W
TI DRV8952 (PWP)	24.5 °C/W	H-bridge driver, larger pad copper

That is roughly a three-to-four-times improvement over the ~100 °C/W leaded part, and it comes with a condition: the pad only works when it is soldered to copper. The TLC5940 datasheet plots the same package with the PowerPAD soldered and unsoldered, and the difference is large — an unsoldered pad throws away most of the benefit. The design rule follows directly: if the part dissipates more than a few hundred milliwatts, choose the exposed-pad (HTSSOP/PWP) option and give the pad a via array to an inner plane. A bare TSSOP-28 hits its thermal limit first. For a board-specific estimate, use the low ψJT (0.6 °C/W for the TLC5940) with a measured top-of-package temperature.

A quick worked example shows the stakes. Dissipate 250 mW in a bare leaded TSSOP-28 at ~100 °C/W and the junction rises about 25 °C above ambient; at an 85 °C ambient that lands near a 110 °C junction — under the usual 150 °C limit, but with thin margin. Put the same 250 mW into the TLC5940 HTSSOP at 36.7 °C/W and the rise is about 9 °C. Push to 1 W and the gap is decisive: the leaded part would notionally rise about 100 °C, over the limit at any warm ambient, while the exposed-pad part rises roughly 37 °C. Above a few hundred milliwatts on a TSSOP-28, the pad stops being optional.

TSSOP-28 vs the alternatives

When a 28-lead part is on the table, these are the packages an engineer actually cross-shops. Pitch, size, height, thermal and hand-solderability side by side:

Package (28-lead)	Pitch	Body L × W	Height	RθJA	Hand-solder
TSSOP (PW)	0.65 mm	9.7 × 4.4 mm	1.2 mm	~100	Yes, with care
HTSSOP (PWP)	0.65 mm	9.7 × 4.4 mm	1.2 mm	25–37	Difficult (pad)
SSOP / QSOP	~0.635 mm	~10.2 × 5.3 mm	~2.0 mm	higher	Yes
SOIC-28 (wide)	1.27 mm	~17.9 × 7.5 mm	~2.65 mm	moderate	Easy
VQFN-32	0.5 mm	5.0 × 5.0 mm	1.0 mm	~34	No — reflow

The TSSOP and HTSSOP figures come from TI datasheets (TCA9548A for the leaded magnitude, TLC5940 and DRV8952 for the exposed pad); the SSOP/QSOP and wide-SOIC entries are family-typical and should be confirmed against the specific part’s drawing, and the VQFN row is the common 32-lead step-down (TLC5940 RHB) rather than a 28-lead part. The pattern is stable: TSSOP-28 is the middle path — finer and thinner than SOIC, more solderable and reworkable than QFN, and warmer than either a QFN or a well-vias exposed pad.

Sourcing, MSL, and compliance

Standard TSSOP-28 parts are usually MSL 1 — unlimited floor life at a 260 °C reflow. TI’s MSP430G2553IPW28 is MSL 1 per its package addendum. The exposed-pad HTSSOP-28 version of a comparable part is not: TI’s TLC5940PWP is MSL 2, with a one-year floor life once the dry-pack is opened. The leaded package saves you a bake regime that the exposed-pad and QFN options impose.

The standard lead finish is NIPDAU (matte tin over nickel-palladium); commodity parts are RoHS-compliant. In tape and reel, a 28-lead TSSOP typically ships 2,000 parts per 330 mm reel on 16 mm carrier tape (both the MSP430 PW28 and the TLC5940 PWP ship this way).

On cost, the package is cheap and the silicon sets the price. A jelly-bean MCU in this footprint — the MSP430G2553 in 20- and 28-pin TSSOP — runs in the low single dollars: the 20-pin MSP430G2553IPW20 lists at $3.33 in single units at DigiKey, but with an 18-week factory lead time (August 2026). The lesson is availability, not unit cost: even a commodity part in a standard package can carry a long lead, so check stock and lead time per orderable, not per package.

Second sourcing within a family is a real advantage here. The entire MSP430G2x13/G2x53 line — G2153, G2213, G2253, G2313, G2353, G2413, G2453, G2513 and G2553 — shares the identical PW28 footprint, so a memory or peripheral change is a drop-in swap on the same land. Across vendors, MO-153 being an open registration means logic and interface parts in TSSOP-28 usually have pin-compatible alternates as well.

Design and assembly mistakes that cause returns

• Building the land to the body width. Draw the footprint to the ~5.8 mm lead span, not the 4.4 mm body — pads sized to the body leave the feet with nothing to wet to.
• Reusing a 24-lead footprint verbatim. The pad and pitch are the same, but a TSSOP-28 needs two more pads per side and a longer courtyard; dropping a 28-lead part on a 24-lead land shorts or leaves leads unconnected.
• Pin-1 mirrored. The silkscreen dot must agree with the package pin-1 mark and the reel’s pin-1 quadrant (Q1 for the TLC5940 PWP reel). Mirror it and every placement lands 180° out.
• Flooded thermal pad. On HTSSOP-28 variants, full paste coverage on the pad causes float and voids. Window it to ~70–80% and tent or plug the vias.
• Solder bridges by hand. 0.65 mm pitch across 14 leads a side is hand-solderable but unforgiving; drag-solder with flux and wick the bridges.
• Assuming MSL 1. The standard part is MSL 1, but the exposed-pad version of the same function is MSL 2 — read the reel label, not the generic value.

Frequently asked questions

What are the dimensions of a TSSOP-28 package?

The body is 9.6–9.8 mm long and 4.3–4.5 mm wide, at most 1.2 mm tall, with leads on a 0.65 mm pitch and a 6.2–6.6 mm span across the lead tips (Monolithic Power drawing MF-PO-D-0024, JEDEC MO-153 variation AE). Standoff is 0.05–0.15 mm and lead-foot length is 0.45–0.75 mm.

What is the difference between TSSOP-24 and TSSOP-28?

They share the 4.4 mm body width, 6.4 mm lead span, 0.65 mm pitch and 1.2 mm maximum height. The TSSOP-28 is simply longer — a 9.7 mm body versus 7.8 mm — carrying 14 leads per side instead of 12. Footprints use the same pad and pitch, with two extra pads per side.

What is the pin pitch and footprint of a TSSOP-28?

The pin pitch is 0.65 mm. The recommended land uses 28 pads, each 1.60 mm × 0.40 mm, on that 0.65 mm pitch, with a 5.80 mm span between the two rows (MPS MF-PO-D-0024). Match the IPC-7351 density level to your assembly process rather than defaulting to the tightest land.

Is a TSSOP-28 the same as an HTSSOP-28?

No. An HTSSOP-28 is a TSSOP-28 with an exposed thermal pad on the underside (TI brands it PowerPAD). Outline and pinout match, but the footprint adds the pad and vias, and the moisture rating differs — standard TSSOP-28 is often MSL 1 while the exposed-pad version is MSL 2. Choose HTSSOP when the part runs warm.

Can you hand-solder a TSSOP-28?

Yes. The 0.65 mm pitch is manageable with a chisel tip, plenty of flux and solder wick for bridges; drag-soldering works well across all 14 leads per side. It is harder than an SOIC and easier than a QFN, which has no accessible leads and effectively needs reflow or hot air. The exposed-pad version is harder because the pad needs reflow or a hot plate.

How many pins does a TSSOP-28 have, and what does the 28 mean?

Twenty-eight leads — 14 on each long side. The TSSOP family spans 8 to 80 leads; on the 4.4 mm body used for 28 leads, the count fixes the 9.7 mm body length given the 0.65 mm pitch. TI’s MSP430G2553 in the PW28 package is a common 28-lead TSSOP example.

The bottom line

Choose a TSSOP-28 when you need a fine-pitch, sub-1.2 mm leaded part with a bit more I/O than a 24-lead offers, it still inspects and reworks by hand, and the silicon stays under a few hundred milliwatts. Draw the footprint to the 5.80 mm land, add the two extra pads per side if you are extending a TSSOP-24 library, match the pin-1 mark to the reel quadrant, and read the MSL off the actual reel. If the part runs warm, step to the exposed-pad HTSSOP-28 and via the pad to copper. If you need it smaller or cooler still and own a reflow line, a 32-lead VQFN is the next move. Whichever you pick, match the vendor drawing to the exact part number before you release the library.