LPUART vs UART for SLM

Question

Hello, 
 We are developing a board with both nrf91 and nrf54 boards. We are looking to make the nrf91 a SLM with a UART interface to support the LTE functionality of the nrf54. 
 We had some questions around this implementation, noting that we are highly power constrained. 
 1. D o we need to use LPUART or do the new chips have a power efficient UART which makes LPUART unnecessary ( Is there a significant difference between LPUART and standard UART?) 
 2. What is the estimated power draw of the LPUART and UART when not transmitting data? 
 3. Is LPUART supported on the nrf9151? Thanks in advance!

SwRa · Accepted Answer

Hi Sam, 
 LPUART (Low Power UART) is specifically designed to reduce power consumption compared to standard UART. The standard UART peripheral, when enabled (especially in receive mode), keeps the high-frequency clock running and draws significant current even when idle. LPUART achieves lower power by using additional handshake lines (REQ/RDY) to allow the UART to be fully disabled when not in use, waking only when needed for data transfer. You can refer this discussion as well: Using low-power VS non low-power mode peripherals 
 The LPUART can be fully suspended when not in use, reducing the current draw to the system's sleep current (which can be in the range of a few microamps, depending on the chip and configuration). When enabled, the UART peripheral can draw around ~1 mA constantly, even when not transmitting or receiving data, because it keeps the HFCLK running. 
 3. Is LPUART supported on the nrf9151? 
 It is supported on the RF9160 SoC, I expect it to be supported in the nRf9151 as well.. But I can see that it is not listed in the supported boards in the sample. I will check this with the team and get back to you. 
 Regards, 
 Swathy

LPUART vs UART for SLM

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