STLED316SMTR 6-Digit LED Controller with Key Scan — Specs, Pinout, Alternatives & Sourcing (2026)

What is the STLED316SMTR and why use it for 6-digit LED panels?

The STLED316SMTR is a STMicroelectronics serial-interfaced 6-digit LED controller with integrated key scan, housed in a 24-pin SO-24 surface-mount package (verified from the XAIPART product database, accessed 2026-10-06). It exposes 14 open-drain driver outputs split as 8 segment lines (SEG0–SEG7) plus 6 digit commons (DIG0–DIG5); each segment output is rated at 40 mA continuous sink current (verified). A built-in 2×2 key-scan matrix supports up to 4 mechanical keys without external diodes, and the 3-wire SPI-compatible interface (CLK, DIN, STB) keeps the host MCU pin budget low.

The IC runs from a single 4.5 V to 5.5 V supply on VDD, drives LEDs with up to 3 V forward voltage, and operates across the industrial -40 °C to +85 °C range. The MTR suffix denotes tape-and-reel packaging for high-volume SMT assembly, and the part is RoHS-compliant (Pb-free). Lifecycle status is active, with 99999 units of verified distributor stock on file. Reference pricing starts at $1.85 at quantity 1 and falls to $1.02 at quantity 1,000 (verified as of 2026-10-06). MOQ is 1 unit; lead time is typically stock to 8 weeks from authorised distributors including Mouser, DigiKey, and the ST eStore.

For an engineer evaluating a 6-digit 7-segment front panel, the STLED316SMTR consolidates display multiplexing, key scanning, and current regulation into a single SO-24 part, replacing roughly 10 discrete components compared with a software-multiplexed MCU-only design.

How do you design in the STLED316SMTR for a 5 V 6-digit front panel?

Designing in the STLED316SMTR follows the standard ST 7-segment controller pattern: bring up the supply, program the display through the 3-wire serial interface, and dimension the external RSET and decoupling network against the verified 40 mA per-segment sink rating. Below is a step-by-step procedure that maps each design decision to a verified spec.

Step 1 — Supply, decoupling, and grounding

Power the STLED316SMTR from a clean 4.5 V to 5.5 V rail on VDD (pin 23). Place a 100 nF X7R decoupling capacitor within 3 mm of VDD and a 10 µF bulk capacitor on the same net to suppress transients during display multiplexing. Because each digit can pull 8 segments × 40 mA = 320 mA at peak, the bulk capacitor must source that current without dipping VDD below the 4.5 V minimum. Tie GND (pin 4) to a low-impedance ground plane; the open-drain sinks depend on this return path for accurate current regulation.

Step 2 — RSET and segment current

The verified maximum segment output current is 40 mA per segment open-drain. The datasheet's typical application circuit shows the recommended RSET resistor value for a given target brightness; consult the STMicroelectronics datasheet for the precise formula. As a starting reference, with a 5.0 V VDD and a red 7-segment LED with Vf ≈ 2.0 V at 20 mA, headroom across the external current-setting network is roughly 3.0 V, comfortably supporting the 40 mA per-segment ceiling from the verified spec.

Step 3 — Wiring the 3-wire SPI-compatible interface

The serial interface uses three pins: STB (strobe/chip-select, active high, pin 1), CLK (serial clock, pin 2), and DIN (serial data input, pin 3). Configure the host MCU peripheral for SPI mode 0 (CPOL=0, CPHA=0) per the verified FAQ entry, and drive STB high only during command writes. The interface is write-only from the host, simplifying firmware: a single SPI peripheral plus one GPIO is sufficient.

Step 4 — Driving the 7-segment panel

Connect SEG0–SEG6 to segments A–G of a common-anode or common-cathode 7-segment display, and SEG7 to the decimal point. Wire DIG0–DIG5 to the six digit commons through per-digit current-limiting resistors where required by the panel topology. Because the verified FAQ notes the open-drain outputs support both common-anode and common-cathode panels, the same STLED316SMTR part number can be reused across mixed display inventories.

Step 5 — Key-scan matrix wiring

The integrated 2×2 key-scan matrix uses pins KS0 (pin 19), KS1 (pin 20), KI0 (pin 21), and KI1 (pin 22). Each intersection supports one mechanical switch, giving up to 4 keys total without external diodes. The built-in debounce logic removes the need for host-side debounce code, freeing MCU cycles for the main application. Wire switches between KS rows and KI columns as shown in the datasheet's key-scan reference design.

Step 6 — Thermal and PCB layout notes

The 24-pin SO package has a 7.5 mm body width and dissipates heat primarily through the copper pours on the segment/digit traces. With 14 outputs at 40 mA continuous capability and a 1/6 multiplex duty cycle per digit, average per-segment current is 40 mA × 1/6 ≈ 6.7 mA, well within the SO-24 thermal envelope for the -40 °C to +85 °C industrial range. Keep high-current SEG/DIG traces short and wide, and flood the area under the IC with a ground pour.

Engineer takeaway: a working STLED316SMTR front panel needs only VDD decoupling, an RSET resistor, the 14-segment/digit PCB traces, and 4 key pads — total external BOM is roughly 6 to 10 passive components.

Which parts are direct drop-in alternatives for the STLED316SMTR?

The STLED316SMTR occupies a narrow niche: 6 digits, 14 open-drain outputs, 5 V supply, 3-wire SPI, SO-24. The verified XAIPART database lists four alternatives, summarised in the table below. Only the STLED316SMTR column carries fully verified specifications; alternative columns use only the data explicitly provided in the verified alternative entries.

Per the verified FAQ, the STLED316S is the closest same-brand drop-in because it shares the SO-24 pinout and die family. The STLED316M is also a SO-24 footprint match but carries a segment-current specification difference noted in the verified alternative entry as '-5 mA vs -40 mA'; the STLED316SMTR's verified maximum segment output current is 40 mA, so designers substituting the STLED316M should verify the lower rating against their brightness target before PCB respin. The TM1637 matches the SO-24 footprint but uses a 2-wire proprietary interface, requiring firmware changes (verified). The TM1638 supports 10 digits but requires a larger SO-28 footprint, so it is NOT a same-footprint drop-in (verified).

Engineer takeaway: for true PCB drop-in with no firmware changes, stay within the STLED316 family. The TM1637 fits the SO-24 footprint but forces a firmware rewrite for the 2-wire protocol.

What is the current supply and lifecycle position of the STLED316SMTR?

The STLED316SMTR is in active production (verified lifecycle status: active) and is broadly stocked at authorised distributors. The XAIPART product database lists 99999 units of stock as of 2026-10-06, with a minimum order quantity of 1 unit. Authorised distribution channels include Mouser, DigiKey, and the STMicroelectronics eStore (verified), all of which can typically ship small quantities immediately.

Verified pricing tiers (as of 2026-10-06)

The active lifecycle designation means STMicroelectronics is still releasing the part in production volumes, with no end-of-life or last-time-buy notice on file. The verified base price of $1.02 sits at the qty-1000 tier and represents a 45% reduction from the $1.85 qty-1 entry point. Lead time per the verified FAQ is typically stock to 8 weeks depending on order volume; sample quantities ship immediately. The ST eStore is recommended for scheduled production orders above 5,000 units to avoid independent-broker supply.

Procurement risk flags

• Counterfeit risk: the SO-24 tape-and-reel format is a common counterfeit target. Source exclusively from authorised distributors (Mouser, DigiKey, ST eStore) and verify date code and lot traceability on incoming inspection.
• Demand spikes: display-driver ICs historically see demand spikes during appliance and industrial HMI design-in cycles. Place production orders 8-12 weeks ahead of need to buffer against allocation events.
• RoHS verification: the part is RoHS-compliant (Pb-free) per the verified spec; however, automotive and medical buyers should request the full material declaration and conflict-mineral report directly from STMicroelectronics before approving the part for end-product qualification.

Engineer takeaway: with active lifecycle status, 99999 units of verified stock, and 5 price breaks ending at $1.02, the STLED316SMTR is currently a low-risk, low-cost-procurement part for both prototyping and high-volume runs.

What should buyers watch when sourcing the STLED316SMTR in 2026?

Four near-term trends will shape STLED316SMTR sourcing and design-in decisions through 2026, each anchored to a verified spec or pricing data point.

1. Front-panel interface migration

The 3-wire SPI-compatible interface (CLK, DIN, STB) on the STLED316SMTR remains a strength when paired with low-pin-count MCUs. Buyers planning 2026 and 2027 production should confirm with STMicroelectronics FAEs whether an I²C variant is on the family roadmap. Locking the SPI timing into new PCB layouts without that confirmation creates respin risk if the interface migrates within the product lifecycle.

2. LED forward-voltage envelope

The verified LED forward-voltage range is 'up to 3 V', which covers standard red, green, yellow, and amber 7-segment displays. White and blue 7-segment LEDs with Vf above 3.0 V sit at the edge of this envelope and may exhibit reduced headroom at 5.0 V VDD. Designers targeting white or blue indicators should build a brightness sample and measure margin against the verified spec before committing to production volumes.

3. Price floor at volume

The verified qty-1000 unit price is $1.02 as of 2026-10-06, a 45% reduction from the $1.85 qty-1 price. Volume buyers planning 2026 production runs should request annual-volume quotes directly from the ST eStore or authorised distributors, which historically yield pricing below the listed tiers. Cross-reference the STLED316 family datasheets on the official STLED316SMTR product page for the latest authorised-channel pricing.

4. Key-scan count for richer HMIs

The integrated 2x2 key-scan matrix supports up to 4 keys (verified). Designs requiring 6, 8, or more front-panel buttons will need an external key-scan expander or a different controller. For designs that may evolve beyond 4 keys, evaluate the SO-24 pin budget early so the workspace holds.

For deeper context on companion front-panel ICs, MCUs, and clocking parts used alongside the STLED316SMTR, see the XAIPART guides on the SI53112-A00AGM zero-delay buffer, the PIC32MX795F512H-80V/PT MCU, and the PIC32MX564F064H-I/PT. The full XAIPART component catalog and technical blog index cover hundreds of similar pillar references.

Engineer takeaway: lock the SPI interface, verify Vf margin for non-red displays, push for annual-volume pricing below $1.02, and confirm key-scan headroom before committing the SO-24 footprint to a multi-year production run.