The BU1851GUW key encoder IC is an 8x8 keyboard encoder IC that supports 64 keys and is compatible with QWERTY keyboards. It adopts the architecture that the information of the only key whose status is changed, such as push or release, is encoded into the 8 bits data. This can greatly reduce the CPU load which tends to become heavier as the number of keys increase. (Previously, all key's status is stored in the registers.) Furthermore, auto sleep function contribute to low power consumption, when no keys are pressed. It is also equipped with the various functions such as ghost key rejection, N-key Rollover, Built-in power on reset and oscillator.
This technical note introduces the BU1851GUW key‑encoder IC, which can monitor up to a 8 × 8 matrix (64 keys) and provides functions such as ghost‑key rejection, N‑key rollover, and an auto‑sleep mode for low power consumption. The document details the device architecture, pin assignments, functional block diagram, and typical application circuits.
The note also lists absolute maximum ratings, operating conditions, package specifications, and the 3‑wire communication protocol used to transfer encoded key data to a host controller. Ordering information and legal notices are included at the end of the document.
| Supply voltage range (VDD) | 2.20 V – 3.60 V |
|---|---|
| Input voltage range (Vin) | -0.2 V – (VDD + 0.2 V) |
| Operating temperature range | -30 °C – +85 °C |
| Stand‑by current | < 5 µA |
| Package power dissipation | 272 mW |
| External clock frequency (CLKSEL) | 0.8 MHz – 1.2 MHz |
| External resistor (Rxi) | 118.8 kΩ – 121.2 kΩ |
It can monitor up to a 64‑matrix (8 × 8) of keys, i.e., 64 keys.
The device enters standby when XRST is set high; it then waits for a key press.
POREB enables the power‑on reset; it is active low and must be low for the reset to function.