[FAQ] DS320PR810: Does redriver power consumption vary with data rate?

Applicable to all TI PCIe redrivers for Gen 4:

• DS160PR410, DS160PR810, DS160PR1601, DS160PR412, DS160PR421

And Gen 5 devices as well:

• DS320PR410, DS320PR810, DS320PR1601, SN75LVPE5412, SN75LVPE5421

Intuitively, it may seem like there should be a connection between data rate and power consumption. In PCIe Gen 4, bits are transmitted at a rate of 16 GHz for example, and at Gen 5 this rate is doubled to 32 GHz. Even when the root complex and endpoint aren't intending to send any data to each other, the PCIe transmitters will constantly send idle bits to maintain the link. In integrated circuits, power consumption is often associated with the switching behavior of amplifiers, so it could appear that the power consumption would be higher at a data rate where the output amplifier must switch twice as frequently. However, TI redrivers use an architecture with a relatively constant current output at all times and the frequency of switching has little effect on the overall power draw. As such, the power consumption of a TI redriver given in its respective datasheet is applicable to all data rates that the device might be operating at.

Note that this constant power consumption is a characteristic of linear redrivers, which only boost signals using analog methods. Retimers, more complex ICs that have digital functions such as clock data recovery (CDR), are expected to have variable power consumption based on the data rate. Indeed, many PCIe endpoints have their own comprehensive CDR subsystems and experience the same effect. The heatsink of a network card operating at PCIe Gen 5 may feel hot to the touch, but only somewhat warm when running at Gen 4.