Power Reference Design for Nvidia CPU Processor Offers Insights into Crypto Mining

By now nearly everyone is familiar with Bitcoin (BTC), from its recent peak of over $64,000 per BTC to its current price just north of $21,000. 

 

Bitcoin, Crypto and Proof of Work Validation

BTC is the most well known digital cryptocurrency and is the leading example of a peer-to-peer electronic cash system where people can transfer money anywhere across the globe, the same as passing a dollar bill across the counter at your local store.

To achieve this, the network uses a proof of work (PoW) blockchain protocol to guarantee the unique digital characteristics of each BTC and to ensure that each blockchain transaction is properly validated. To maintain the integrity of the network, all BTC transactions, including the supply of new BTC, are validated by “digital miners” who compete to solve a SHA-256 based hashing algorithm using specialized processors. Generating the proper hash is computationally intensive, but it is this effort that ensures the integrity of the Bitcoin blockchain…and consumes quite a bit of power.

 

Peer-to-peer electronics cash transactions. Image used courtesy of Experian

 

Powering the Hashing Processors in Crypto Mining

With BTC prices rising significantly recently, Bitcoin mining has grown as an industry. Comprised of both small and large operators, these “digital miners” connect their hash processing hardware to the blockchain, validating on-chain transactions in exchange for mining rewards paid out in crypto.

At the heart of these crypto mining devices are the processors – GPUs, CPUs and ASICs designed with the specific task of solving the hash as quickly and with as little power as possible.

Power is the key to crypto mining, but how is power delivered to these processors?

 

Bitcoin Miner. Image used courtesy of Bitmain

 

Nvidia Tegra T40/T50 Core Processor Power Reference Design

The PMP9128 from Texas Instruments (TI) provides a reference design for powering the Nvidia Tegra CPU and may offer insights for designing board level CPU power for a crypto mining unit.

While Tegra is not the latest generation CPU and is marketed primarily for automotive infotainment applications, much of this power architecture might be translated to crypto mining applications.

To start, the reference design parameters are set as follows:

 

Specification	Parameter
Vin (Min) (V)	6
Vin (Max) (V)	19
Vout (Nom) (V)	1.1
Iout (Max) (V)	15
Output Power (W)	16.5
Isolation	Non-Isolated
Input Type	DC
Topology	Buck-Multiphase

PMP9128 Design Parameters. Image used courtesy of TI

 

In this design, a standard 12 V input is converted, without isolation, to a load voltage of 1.1 V capable of delivering 15 A, or 16.5 W of power to the processor. The schematic BOM has about 50 total components, including 7 active devices.

The main controller for the power conversion is the TPS51632, step down controller with dual PWM outputs designed specifically to power Nvidia CPUs. The design then uses two each of the TPS51604 half bridge gate drivers and CSD87381P 30-V, N channel synchronous buck NexFET™ half bridge power blocks.

Last are two Low Drop Out (LDO) regulators (TPS73101) to generate the internal voltage rails (3.3 V and 1.8 V) for the other active components and I2C interface. The design assumes 5 V is already available at the board level, along with VIN as specified above. All passives are standard components, which is a huge benefit from a cost and supply management perspective. The inductor (L1) is the PIFE25201B-R22MS-63, SMD, powdered iron, 220 nH, 7 A, 0.008 ohm which is still in production, but a suitable replacement could be used.

 

Partial PMP9128 reference schematic. Image used courtesy of TI

 

While the design parameters specify a load of 15 A, each power block can handle up to 25 A with airflow and heat sinking. With this type of thermal management in place the dual channel configuration of the reference design can accommodate up to 50 A of load current.

 

Operating Current	No Airflow	15	A
	With Airflow (200 LFM)	20
	With Airflow + Heat Sink	25

Power Block (CSD87381P) operating current limits. Image used courtesy of TI

 

In addition to the full schematic and BOM, the published reference design also offers a full test report and PCB layout files. The total board area of the supply is 234 mm², including the input and output capacitors and inductor.

 

Scaling to Higher Power Levels

Today’s Bitcoin and other crypto mining machines using the latest processor technologies will likely need more power. However, this reference design should scale as needed through the addition of more dual channel controllers, drivers and FETs operating in parallel to meet higher load requirements.

With aggressive thermal management to include airflow and heat sinking, doubling the channel count of the reference design should accommodate up to 100 A. The latest Cmp Hx GPU from Nvidia for professional mining operations has a rated power level ranging from 125 W to 320 W.

At an output voltage of 1.1 V, as specified in this design, 114 A to 291 A of load current would be required, or up to 12 power blocks and 6 dual channel PWM controllers, again with fans and heat sinks. However, further research is required on parallel load operations with multiple TPS51632 controllers.

 

	30HX	40HX	50HX	90HX
Ethereum Hash Rate(1)	26 MH/s	36 MH/s	45 MH/s	86 MH/s
Rated Power(2)	125 W	185 W	250 W	320 W
Power Connectors(2)	1 x 8-pin	1 x 8-pin	2 x 8-pin	2 x 8-pin
Memory Size	6GB	8GB	10GB	10GB
Starting Availability	Q1	Q1	Q2	Q2

¹Ethereum hash rate applies to the DAG and algorithm in use in Epoch 394 and is provided for reference clocks under room temperature conditions with good cooling.

²Rated Power and Power connectors specified for the reference design. Partner board designs may choose a different configuration.

Nvidia Cmp Hx GPU specifications for professional mining. Image used courtesy of Nvidia

 

Of course, with higher performance comes more cost, space requirements and additional thermal considerations. At the high end, many of the latest processors and mining devices use liquid cooling, in addition to fans and traditional heat sinks, to remove heat and optimize performance and reliability.

 

Closed loop water cooling for Bitcoin miners. Image used courtesy of jetcool

 

Feature image used courtesy of Bitmain