SBOSA45C february 2022 – may 2023 TMP1826
PRODUCTION DATA
The bus pullup resistance value selected is important for communication as per the speed mode and ensuring that minimal possible energy is consumed in the application. If the resistor value is too small, the design may violate the VOL limits on the SDQ pin.
Consider the total SDQ pins and bus capacitance along with the bus leakage current when selecting the pullup resistor. The pullup resistance value selected must also ensure that the signal level reaches VIH as per the timing requirements for standard and overdrive mode.
In bus powered mode of operation, the device charges the internal capacitor through the SDQ pin and the pullup resistor. This charge on the capacitor is used during bus communication, when the SDQ pin low. For other high current functions like thermal conversion and EEPROM access, the bus is held idle to ensure that the device can draw current through the pullup resistor. The SDQ pin voltage during the high current operation must be maintained to ensure sufficient operating margins. For VPUR ≤ 2.0 V, use Equation 1. For VPUR > 2.0 V, use Equation 2 to calculate the pullup resistor value.
When the device is used in VDD or supply powered mode, a larger pullup resistor value may be used, as the SDQ pin is used only for communication. The user must ensure that the pullup resistor value selected must be able to support the timing for the required bus speed of operation.
For low current consumption devices like the TMP1826, selecting the correct pullup resistor value allows the application to avoid low impedance current path components for bus powered mode of operation while maintaining communication speeds and device parameters as per its electrical specification. For multiple devices on the bus, a low impedance current path is recommended.