Article: Power Delivery in a Modern Processor
By: Jason Creighton (asdf.delete@this.example.com), May 12, 2020 8:15 am
Room: Moderated Discussions
Travis Downs (travis.downs.delete@this.gmail.com) on May 12, 2020 7:53 am wrote:
> What is the purpose of the LDO? Does it even reduce power draw? The voltage drop is a dead loss
> in an LDO, in the sense that the reduced power I * (Vin - Vout) is just dissipated in the regulator,
> but is there a secondary effect that saves power? Or is it just to better control the voltage
> for another purpose (one could be to move power dissipation away from the core)?
Linear voltage regulators (eg, an LDO) are used to produce a cleaner power rail with less ripple compared to switching regulators. When a really clean voltage rail is required, it's not uncommon to have a switching power supply (in this case, the motherboard VRM) that gets "close" to the desired voltage followed by a linear regulator (the on-die LDO) to smooth it out.
The downside is that, indeed, this burns some extra power, but there's always power loss in power supply design, so it's not necessarily a bad trade-off.
Jason
> What is the purpose of the LDO? Does it even reduce power draw? The voltage drop is a dead loss
> in an LDO, in the sense that the reduced power I * (Vin - Vout) is just dissipated in the regulator,
> but is there a secondary effect that saves power? Or is it just to better control the voltage
> for another purpose (one could be to move power dissipation away from the core)?
Linear voltage regulators (eg, an LDO) are used to produce a cleaner power rail with less ripple compared to switching regulators. When a really clean voltage rail is required, it's not uncommon to have a switching power supply (in this case, the motherboard VRM) that gets "close" to the desired voltage followed by a linear regulator (the on-die LDO) to smooth it out.
The downside is that, indeed, this burns some extra power, but there's always power loss in power supply design, so it's not necessarily a bad trade-off.
Jason