All of the Clockworks mic modules are designed to be used with CFG0 (9 V) bus power. This includes all of the AD242x devices and the AD2433. Parts that use CFG4 (24 V) bus power, such as the AD2437, cannot be used directly. Clockworks offers a line of A2B isolators that can be used should you need to mic AD2437/CFG4 systems with these modules.
For Clockworks boards with UTP (2-pin DuraClik) connectors, the tan color indicates 9 V and the red color indicates 24 V.
Don’t be like this idiot and let the magic smoke out!
Clockworks offers a number of different MEMs microphone boards for use in A2B systems. These boards are all bus powered, which allows considerable flexibility in physical placement as the only wiring needed is for A2B. The boards are based on the AD2427 A2B transceiver – except AB0105, where the module would be AD2428 based. AD242x parts (and AD2433) are what ADI calls CFG0-power devices. The main node nominally supplies up to 9 V at 300 mA. In real life there are several resistances and at full load the main node output will be closer to 8 V. This is the differential DC voltage across the A2B lines; the return side is not at ground (0 V) potential relative to the system supply. The ADI A2B transceiver datasheet details the bus power considerations in detail and should be referred to in aiding your specific configuration modeling.
The minimum AD242x Vin power voltage is 3.7 V. There is a Schottky diode to protect the chip from reverse power; the minimum bus voltage at the A port is around 4.1V. Each node will drop around 0.8 V (not necessarily symmetrically on the supply and return sides). This leads to 5 nodes being usable from the minimum voltage perspective. Each node’s pass-through current is lower so the voltage drop per node reduces the farther down the chain it is, which means when the wind is right 6 nodes may work.
The other way to analyze the number of nodes is to consider the power limit. The main node can supply up to 300 mA. Each quad mic node (the designs are all electrically similar) will draw an average of 40 mA and a worst-case value of 50 mA. The actual current a node consumes is a function of the node and the amount of upstream and downstream data being passed through it. The AD2427 datasheet as well as design resources on the ADI website provide details on power estimation. Even with the 50 mA max assumption that is still 6 boards which is the constraint due to voltage drops.
For the mic boards the AD2427’s internal LDOs are used to provide all voltages; the current draw in nominally the same regardless of the bus voltage at the A port. If your system includes other boards with switching based power sections then bus current drawn will increase at lowered bus voltages.
To create a system with 32 mic channels, i.e. 8 quad mic boards, some sort of mid-span power injection is needed. There are a lot of ways to do that; Clockworks’ AB0020 EVM with the AB0001 module plugged into it is a simple and versatile way as its analog outputs could be used to monitor the mic audio without affecting the system processing. There’s a clever way to use the AB0401 module to inject 9 V, but only if you don’t need fault isolation and the supply itself is current limited to 300 mA. If unsure, ask us first – see rule #1 above about not making smoke.
