Current Limit Configuration
The GlowFlora Home PCB uses an MT9700N — a programmable current limiting switch IC — to protect the LED strip and battery from overcurrent. The MT9700N sets its output current limit via a resistor on its ISET pin: the higher the resistance, the lower the current limit.
Formula:
I_lim (mA) = 6800 / R_set (kΩ)A 3-tier solder jumper matrix — 6 resistors, 9 jumpers — lets you select a current limit for any LED count without reflowing components.
Jumper Options
Each tier has four possible states. Select one state per tier by closing the corresponding jumper(s):
| State | Jumpers to close | R contribution |
|---|---|---|
| bypass | 1 jumper (bypass) | Shorts the tier — 0 Ω |
| A | 1 jumper (A) | R_A |
| B | 1 jumper (B) | R_B |
| A + B | 2 jumpers (A and B) | R_A ∥ R_B (parallel) |
R_set = R_T1 + R_T2 + R_T3
A + B means two physical jumpers
Selecting A + B puts both resistors in parallel and requires closing two jumpers on that tier — one for A and one for B. This is still a single tier selection.
Calculator
| Tier | A | B | A ∥ B |
|---|---|---|---|
| T1 | 3.3K | 20K | 2.8K |
| T2 | 3.9K | 2.4K | 1.5K |
| T3 | 6.8K | 3K | 2.1K |
| LEDs | Target | T1 | T2 | T3 | Actual |
|---|---|---|---|---|---|
| 4 | 288 mA | B | A+B | A+B | 289 mA |
| 6 | 432 mA | A | A | A | 486 mA |
| 8 | 576 mA | A | A+B | A | 587 mA |
| 10 | 720 mA | A | A | A+B | 733 mA |
| 12 | 864 mA | A | A+B | B | 873 mA |
| 14 | 1008 mA | A+B | A | bypass | 1010 mA |
| 16 | 1152 mA | A+B | bypass | B | 1166 mA |
| 18 | 1296 mA | A+B | B | bypass | 1300 mA |
| 20 | 1440 mA | bypass | A+B | B | 1516 mA |
| 22 | 1584 mA | bypass | A | bypass | 1744 mA |
| 24 | 1728 mA | bypass | A | bypass | 1744 mA |
| 26 | 1872 mA | bypass | A+B | A+B | 1906 mA |
| 28 | 2016 mA | A | bypass | bypass | 2061 mA |
| 30 | 2160 mA | bypass | bypass | B | 2267 mA |
| 32 | 2304 mA | A+B | bypass | bypass | 2401 mA |
| 34 | 2448 mA | bypass | B | bypass | 2833 mA |
| 36 ⚡ | 2500 mA | bypass | B | bypass | 2833 mA |
| 38 ⚡ | 2500 mA | bypass | B | bypass | 2833 mA |
| 40 ⚡ | 2500 mA | bypass | B | bypass | 2833 mA |
For an exact limit — solder one resistor to the custom pad and leave all tier jumpers open.R (kΩ) = 6800 / Itarget (mA) · Itarget = N × 60 mA × 1.20
ISET must always have a path to GND — at least one non-bypass tier, or a custom pad resistor.
2.5 A board limit — PCB traces and connector are rated to 2.5 A.