TLC59116: What is the smallest value for Rext?

Hi David,

Theoretically, you should keep the reference current I_ref <= 8mA (120mA / 15 or 40mA / 5, see datasheet Page 20). To get the functional operation, Rext >= V_REXT / I_ref_max = 1.26V * VG / I_ref_max, where VG is the programmable voltage gain. To make the full use of voltage gain range and to ensure the reference current <= 8mA even if the voltage gain is mistakenly set, choose VG = 127/128 and substitute this value into the above equation. This gives Rext >= 1.26V * (127/128) / 8mA ≈ 156.3 ohm.

For a real-life case, you can refer to Figure 1 on Page 9 of the datasheet (note that there is a typo that the output current unit should be mA).

By the way, are you going to push TLC59116 to its maximum output current capability? Is this the reason why you are looking for the minimal Rext value?

Best Regards,

Steven