The nominal output impedance of the MAX9979 is 50Ω. This nominal 50Ω driver output resistance is adjustable by ±2.5Ω with a 360mΩ resolution. This flexibility in output resistance adjustment helps to match load impedance and thus to avoid any kind of reflections on a high-speed signal. It also helps to optimize power transfer.
Driver output impedance can be set using the RO serial bits in the DCL calibration register, as shown in Table 1.
Table 1. Output Resistance Control
| SERIAL-INTERFACE BITS | DRIVER OUTPUT RESISTANCE (Ω) | |||
|---|---|---|---|---|
| RO3_ | RO2_ | RO1_ | RO0_ | |
| 0 | 0 | 0 | 0 | RO - 2.88 |
| 0 | 0 | 0 | 1 | RO - 2.52 |
| 0 | 0 | 1 | 0 | RO -2.16 |
| 0 | 0 | 1 | 1 | RO - 1.80 |
| 0 | 1 | 0 | 0 | RO - 1.44 |
| 0 | 1 | 0 | 1 | RO - 1.08 |
| 0 | 1 | 1 | 0 | RO - 0.72 |
| 0 | 1 | 1 | 1 | RO - 0.36 |
| 1 | 0 | 0 | 0 | RO + 0* |
| 1 | 0 | 0 | 1 | RO + 0.36 |
| 1 | 0 | 1 | 0 | RO + 0.72 |
| 1 | 0 | 1 | 1 | RO + 1.08 |
| 1 | 1 | 0 | 0 | RO + 1.44 |
| 1 | 1 | 0 | 1 | RO + 1.80 |
| 1 | 1 | 1 | 0 | RO + 2.16 |
| 1 | 1 | 1 | 1 | RO + 2.52 |
*Power-on-reset and RST default value.