Servo and high-speed BLDC designers face a packaging contradiction: optical encoders deliver the resolution but not the size, speed or contamination tolerance; Hall-based commutation delivers the robustness but not the resolution. Magnetic encoders close the gap, and the KTH7812 from CONNTEK pushes it further than most — 16-bit absolute angle, one-microsecond update latency, and an operating envelope that reaches 120,000 rpm.
The short answer
The KTH7812 is the encoder to specify when your motor spins too fast for optical encoders, needs absolute position at power-up, and must output standard ABZ/UVW signals to an existing drive — with SPI underneath for configuration and diagnostics.
Verified key parameters
From the KTH7812 product manual (CONNTek, @3.3 V supply):
| Parameter | Value | Condition / Note |
|---|---|---|
| Resolution | 16-bit absolute angle | 65,536 counts/rev |
| INL (non-linear error) | ±0.35° | |
| Output noise (1σ) | 0.015° | |
| Temperature drift | 0.002°/°C | |
| Update latency | 1 µs | Angle refreshed every microsecond |
| Startup time | 1 ms | |
| Supply | 3.0–3.6 V (3.3 V) or 4.5–5.5 V (5 V) | Both supported |
| Working current | 11.6 mA @ 3.3 V | 13.6 mA @ 5 V |
| Magnetic field range | 30 – 150 mT | 60 mT typical operating point |
| Maximum speed | 120,000 rpm | |
| ABZ output | Programmable 4–4096 steps/rev | With hysteresis and index Z |
| UVW output | Programmable 1–8 pole pairs | For BLDC commutation |
| Interface | SPI, registers + MTP | CRC output on SPI |
| Diagnostics | Field-strength detection/alarm | On-chip |
| Package | QFN-16L | |
| Temperature | −40 to +125 °C | |
| ESD | ±5 kV HBM |
The three specs that decide motor designs
1 µs latency, 120,000 rpm. An optical encoder sampling at a few kHz turns to mush above a few thousand rpm — quantisation eats the electrical angle faster than the drive can use it. The KTH7812 refreshes absolute angle every microsecond. At 120,000 rpm (2 kHz mechanical), the rotor moves 0.72° per sample; at servo speeds of 6,000 rpm it moves 0.036° — the encoder is never the bottleneck in the loop.
±0.35° INL with 0.002°/°C drift. For commutation, angle error is torque ripple. A ±0.35° envelope with near-zero thermal drift keeps ripple stable across a temperature cycle — the difference between a drive that tunes once at 25 °C and one that retunes itself every time the housing warms up.
Programmable ABZ and UVW. Existing drives speak ABZ (incremental with index) or UVW (commutation sectors). The KTH7812 configures either over SPI — 4 to 4096 ABZ steps per revolution, 1 to 8 UVW pole pairs — and stores the configuration in on-chip MTP. One encoder SKU then serves multiple drive platforms, which distributors and motor plants both appreciate.
In-axis and off-axis, both supported
The manual covers in-axis (magnet on the rotor shaft end), off-axis (magnet ring on a rotating disc, sensor reading laterally) and multi-pole-pair magnet installation, with recommended magnet geometries for each. Off-axis mounting — the one that lets you keep the motor shaft untouched — is where magnetic encoders displace optics in compact servos, gimbal motors and robot joints.
The field-strength diagnostic deserves mention: the encoder monitors magnet field strength and raises an alarm if the magnet shifts or degrades — a free health-check on the mechanical assembly that optical encoders cannot offer.
Integration notes
- Two voltage worlds — 3.3 V and 5 V variants with matching field and current specs; the 5 V part simplifies legacy drive interfaces
- CRC on SPI reads — angle data over a noisy cable benefits from the built-in CRC option in electrically hostile environments
- Zero-point programming — mechanical zero is set via register, removing the manual alignment step optical encoders need at install
- Hysteresis on ABZ — configurable, to prevent edge chatter at sector boundaries under vibration
Frequently asked questions
Can it replace an optical encoder on an existing servo?
Electrically yes — ABZ output with programmable steps/rev and an index pulse is the standard drive interface. Mechanically you add a diametral magnet to the shaft and mount the QFN-16L at the specified gap. Off-axis installations need the calibration procedure from the manual (register-based, no physical shimming).
What magnet does it need?
Any diametral magnet producing 30–150 mT at the die — 60 mT is the typical operating point. The manual specifies magnet material and geometry per installation type; NdFeB diametral magnets are the default.
How does 120,000 rpm compare with optical encoders?
Optical encoders typically top out between 10,000 and 30,000 rpm — the LED and the code disc set the ceiling. The KTH7812's solid-state sensing with 1 µs updates is specified to 120,000 rpm, which is why it appears in high-speed spindle and turbo-machinery designs.
Does it do commutation for BLDC directly?
Yes. UVW output with 1–8 programmable pole pairs feeds gate drivers directly for six-step or FOC startup, and the SPI absolute-angle readback serves the FOC closed loop once running.
Sourcing note
The KTH7812 with its full manual, magnet selection guide and reference layouts is available through Mandu. Send your motor's speed, pole count and mounting plan for a selection review, samples and pricing.