PGA460-Q1: Listen INP/INN pins protection feature

Ninomiya-san,

INP and INN are specified to the correct ratings of -0.3V to 2.0V. There is some internal circuitry that has a diode-clipping like effect, but this effect is dependent on the value of the external AC-capacitive coupling capacitors (C_INP and C_INN). This is why calculating the AC-capacitive coupling values (per the equations given in the PGA460 datasheet table 101) is important to prevent damage to the INP and INN pins. Applying a fixed DC value beyond 2.0V without the external AC coupling capacitor will damage the pins, since the coupling capacitors are required to eliminate/remove DC bias.

To synchronize two PGA460 devices, the user has two options:
1) Use two independent communication channels from the MCU to issue commands in parallel. Pros: complete isolation of PGA460 communication per device without any concern for the UART_ADDR value. Cons: Requires an MCU with two USART ports.
2) Use a USART or OWU bus for devices programmed to different UART_ADDR values (up to 8 devices on one bus), and use broadcast commands (listed in PGA460 datasheet table 3) to execute write-only commands simultaneously. Pros: Use of a single bus allows use of a simple MCU. Cons: There is no broadcast command to selectively burst-and/or-listen specific device addresses. Each sensor will need to burst/listen sequentially.

Is the customer attempting to triangulate and track an object by using two PGA460 devices? There is a triangulation code example available in the PGA460 Energia Library and Code Example ( www.ti.com/.../slac741 ), but this assumes there is one PGA460 wired for both transmit and receive, while the other is only wired for receive. I have an in-progress appnote discussing triangulation if this is the customer's intent.