Load & Fan Driver · ZTM-PWM

About this module

Lights, heaters, fans, the odd solenoid: every experiment has a pile of small loads that need switching. The ZTM-PWM handles them all from one ZapLink TWI port.

Twelve low-side PWM channels each switch up to 2 A, with 256-step duty control. Because the switching is on the low side, every load can run from its own supply, anything up to 54 V, or from the board's VIN, which is brought out on the load header for convenience. Each channel's current is measured across its own 50 mΩ sense resistor at the ground end, so a 54 V load is measured just as easily as a 5 V one.

Six 4-wire fan channels run open-loop on PWM or closed-loop to a target RPM, with tachometer readback and stall detection. Each fan's supply is jumpered to VIN or VIN_ALT, so 12 V and 24 V fans can share the board.

Power-up is designed so nothing twitches. A hardware supervisor holds the PWM chip in reset until the supplies are good, and the board signals POWER_SAFE on its ZapLink port when it's ready for the bus. Interrupts from all three chip types share one active-low IRQ line, so the host hears about a stalled fan without having to keep asking.

Loads above 2 A

Switch them through a relay, with the ZTM-PWM channel driving the relay coil.

Inductive loads

Inductive loads require suppression at the load. The on-board TVS provides transient protection only and is not intended as the primary repetitive flyback clamp.

Motors, solenoids, pumps, relay coils and anything else with a coil must have their own flyback diode (or other suppression) fitted at the load. That includes a relay used to switch a bigger load.

Used in these projects

• Cirrus 1 cloud chamber. One board runs the base and side illumination LEDs, the ITO glass heater, the TEC heat-sink fans, and the chamber intake and exhaust fans.
• SonoLuma1 sonoluminescence (in development). Planned for fans and auxiliary loads.

KEY FEATURES

• 12 low-side PWM load channels, 2 A each
• Per-channel current monitoring
• Loads can use any supply up to 54 V
• 6 closed-loop 4-wire fan controllers with tach and stall detection
• Two fan supply rails, selectable per fan
• Hardware-supervised power-up with POWER_SAFE signal