High-current LDOs that play an active role in high-performance processors

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High-performance processors such as the latest FPGAs have extremely strict power supply voltage accuracy requirements. Many people may be wondering, "I want a high-current LDO that can meet the voltage accuracy requirements of FPGAs."

This time, we will introduce the high current LDO lineup of the former Linear Technology Corporation, which is used in the power supply design of the latest high-performance processors, starting with the industry's leading high-current LDO capable of 5A output. Please check if there are any products that can be used in your circuit.

How do you meet the power requirements of high-performance processors?

In recent years, the processes of high-performance processors such as FPGAs, ASICs, and DSPs have become increasingly miniaturized, resulting in dramatic improvements in processing power. As a result, power supply requirements have become lower voltage, and extremely high precision such as "voltage accuracy of ± 1 % or less" is now required. On the other hand, as power consumption continues to increase, the number of locations that require low voltage and high current with high accuracy is expected to increase in the future.

How can you meet the power requirements of high-performance processors? One of these is the use of LDO (Low Drop Out) regulators. By placing an LDO between a DC/DC converter and a high-performance processor, voltage stabilization and high precision can be achieved relatively easily and at low cost.

However, the output current of typical LDOs is limited, and unfortunately they are often not suitable for high-performance processors that require large currents. I hear some people lament, ``I wish I had an LDO with a higher current.''

In fact, the former Linear Technology (LTC) provides high-current LDOs that are used as power supplies for high-performance processors. It has the following features and is ideal for stabilizing the voltage passed from a DC/DC converter.

・Good at voltage conversion with little drop
・High output voltage accuracy
・Contributes to space saving and cost reduction

Even in cases where you have given up on LDO due to insufficient current, you can actively use it.

Additionally, LDOs used to power high-performance processors are often required to have the following functions.

・Fast transient response
・Enable function
・Power good function
・Function to suppress fever

The high-current LDO from the former LTC that we are introducing this time fulfills all of these demands at once.

Introducing the lineup of high current LDOs

Let's introduce the products in detail.

[Lineup (1) LT3070/LT3071] 5A output LDO with ultra-low dropout and fast transient response

The first is the LT3070/LT3071, which boasts an output current of 5A, one of the highest in the industry. Ultra-low dropout voltage, fast transient response LDO.

・ Output adapted to the latest processors

-Output voltage: 0.8V~1.8V

-Can be set digitally in 50mV increments

-Output current: 5A

-Multiple parallel connections possible (output of 10A or more is also OK)

・Suppress fever

-Ultra low dropout voltage: 85mV

-Built-in input voltage tracking function (VOIC)

-Loss can be minimized by controlling the front stage power supply

・Fast transient response

-Minimize output capacitor (minimum 15μF)

・Functions optimized for startup/shutdown of processors

-Enable function

-Power Good

-UVLO

-Thermal shutdown

-Reverse current protection

・LT3071 has analog margining function. Output voltage can be varied continuously.

[Lineup (2) LT3072] 2 channels each capable of outputting 2.5A. Fast transient response LDO

The second one is "LT3072". It is a 2-channel LDO, each capable of outputting 2.5A.

・Output adapted to the latest processors

-Output voltage: 0.6V~2.5V

-Can be set digitally in 50mV increments

-Output current: 2.5A each

・Output accuracy that meets the demands of the latest processors

-Low output noise: 12μVrms (10Hz~100Hz)

・Fast transient response

-Minimize output capacitor (minimum 10μF)

・Functions optimized for startup/shutdown of processors

-Enable function

-Power Good

-UVLO

-Thermal shutdown

-Reverse current protection

[Lineup (3) LT3073] 3A output LDO with ultra-high PSRR and fast transient response

The third one is "LT3073". This is an LDO with very high PSRR.

・Maximize the performance of high-speed converters and RFICs

-Ultra low RMS noise: 1.2μVRMS (10Hz~100kHz)

-Ultra low spot noise: 3nV/√Hz (10kHz)

-Ultra low 1/f noise: 7μVP-P (0.1Hz to 10Hz)

-High frequency PSRR: 52dB (1MHz)

-Dropout voltage: 45mV

・Input voltage range: 0.6V to 5.5V

・Output voltage range: 0.5V to 4.2V (digital setting possible)

・Output current: 3A

-Programmable current limit

-Current monitoring function

・Functions optimized for startup/shutdown of processors

-Enable function

-Power Good

-UVLO

-Thermal shutdown

-Temperature monitoring function

[LT307x series] Comparison table

Let's summarize the features of the LT307x series lineup introduced so far. A comparison of the three products is shown below. Specifications of particular note are output current and dropout voltage.

	LT3073	LT3070-1/LT3071	LT3072
Output current and dropout voltage at that time	3A, 45mV	5A, 85mV	2.5A(2ch), 80mV
Output voltage margining	Digital	LT3070-1: Digital LT3071: Analog	analog
PSRRMore	52dB (at 1MHz)	36dB (at 100kHz)	43dB (at 100kHz)
rms noise	1.2µV (10Hz-100kHz)	25µV (10Hz-100kHz)	12µV (10Hz-100kHz)
VIOC function to control front-stage DC/DC	Yes	Yes	Yes

Why is it important? LDO dropout voltage

Why is low dropout voltage important in LDOs?

Dropout voltage is the minimum difference between the input and output voltages required to obtain the expected output voltage from the LDO. For example, if an LDO 's dropout voltage is 200mV (0.2V), it will require an input voltage of at least 5.2V to output 5V.

The heat generated from an LDO is determined by "input/output voltage difference x output current". A large input/output voltage difference generates more heat, so one of the design points is to minimize the difference as much as possible. However, how far that difference can be reduced depends on the LDO 's dropout voltage specifications. If the dropout voltage of an LDO is large, the range of choices will be reduced.

Furthermore, the size of the output current also affects heat generation. Even if the voltage difference conditions are the same, if the output current is 5 times greater, the heat generation will be 5 times greater. Therefore, reducing the input/output voltage difference is even more important for high-current LDOs.

While the dropout voltage of typical LDOs is around 200mV to 500mV, the LT307x series has an extremely low dropout voltage of 45mV to 85mV. Since the input/output voltage difference can be significantly reduced, the problem of LDO heat generation can be overcome even with large currents.

[Lineup (4) LTM4709] Module type now available! 3ch each 3A high performance LDO

Finally, we will introduce the module type high current LDO"LTM4709". This product maintains the performance of the LT3073 with an output current of 3A and a dropout voltage of 45mV, but enables three channels of output with one chip. All necessary peripheral parts are also built-in.

・Built-in peripheral components necessary for LDO

-Capacitor x 3

-Resistance x 2

・Performance remains the same as LT3073, each channel outputs 3A

-Input voltage range: 0.6V to 5.5V

-Output voltage range: 0.5V to 4.2V (programmable setting)

-Low RMS noise: 1.3μVRMS (10Hz to 100kHz)

-Low spot noise: 3nV/√Hz (10kHz)

-High frequency PSRR: 51dB (1MHz)

-Dropout voltage: 45mV

-Ultra-fast transient response

・Each protection function firmly follows the LT3073.

Let's compare the implementation of an equivalent circuit using a single channel LT3073 and a modular LTM4709. In a circuit configuration using three LT3073s, the total size including peripheral components is 302 mm2. On the other hand, the LTM4709 fits within 145 mm2 including peripheral parts. By choosing the LTM4709, the circuit size can be reduced by approximately 50 %.

LT3073 vs LTM4709, total size comparison at 3A x 3 output — Total size comparison when outputting 3A x 3ch

The benefits are not limited to space savings. The LTM4709, which can cover the multiple power supplies required for high-performance processors, contributes in a variety of ways, including labor-saving design, reduced component count, and board cost reduction.

This time, we introduced Analog Devices (formerly LTC)'s high-current LDO, which is useful in power supply design for the latest high-performance processors. We have a unique lineup including 5A output and module types. Why not add it to your options?

Evaluation boards are available for all of the products listed. If you are interested, please try it.

If you have any questions, please feel free to contact us.