Design Notes
LED Matrix Drive
- Topology: common-anode rows with P-channel MOSFET high-side switches and constant-current column sinks.
- Row decoder outputs are active-low; each selected output pulls one MOSFET gate low.
- 100 kΩ gate-to-source resistors keep rows off if the decoder is unpowered or disconnected.
- 470 Ω series resistors limit 74HCT154 peak gate-charge current and damp switching edges.
- BLANK and ROW_ENABLE_N are pulled up to local +5 V so the display remains disabled if the controller is absent.
Driver Current Programming
- STP16CP05 datasheet table specifies approximately 20 mA per channel with R-EXT ≈ 1.006 kΩ.
- Use 1.00 kΩ, 1% on each driver.
Power Budget
- LED peak: 10 columns × 20 mA = 200 mA.
- Logic and driver allowance: approximately 50 mA.
- Design peak estimate: 250 mA at 5 V.
- Input PTC: 500 mA hold rating.
Multiplexing Sequence
- Assert OE/BLANK to disable column sinks.
- Disable row decoder or select a non-display address.
- Shift 32 bits through the cascaded drivers.
- Pulse LATCH.
- Set ROW_A[3:0] to 0–9.
- Enable the decoder.
- Deassert OE/BLANK for the desired dwell time.
- Repeat for the next row.
Use 2–5 µs dead time after disabling the old row and after enabling the new row during initial firmware bring-up. Shift all 32 bits every update and force unused outputs off.
External Interface Protection
- DATA, CLK, LATCH, BLANK, ROW_A0–ROW_A3, and ROW_ENABLE_N each use 4.7 kΩ series protection.
- SDO_OUT uses a 3.3 kΩ / 6.8 kΩ divider, producing approximately 3.37 V from a 5 V high level.
- The external controller should not actively drive HIGH into an unpowered matrix board; use low or high-impedance states during power sequencing.
Open Layout Constraint
- LED centers must be placed on a 10 mm × 10 mm grid during the PCB-layout phase.