Micromodule (àModule) Power Design
175
Jian Li Gina Le
Dual 13A μModule regulator with
digital interface for remote monitoring
& control of power
point-of-load, the LTM4676 features configurability and telemetry-monitoring of power and power management parameters over PMBus—an open standard I2C-based digital serial interface protocol. The LTM4676 combines best-in- class analog switching regulator performance with precision mixed signal data acquisition. It features ±1% maximum DC output voltage error and ±2.5% current read back accu- racy over temperature (TJ=−40°C to 125°C), and integrated 16-bit delta-sigma ADC and EEPROM.
The LTM4676’s 2-wire serial interface allows outputs to be margined, tuned and ramped up and down at programma- ble slew rates with sequencing delay times. Input and output currents and voltages, output power, temperature, uptime and peak values are readable. The device is comprised of fast, dual analog control loops, precision mixed signal circuitry, EEPROM, power MOSFETs, inductors and supporting components housed in a 16mm × 16mm × 5.01mm BGA (ball grid array) package.
The LTM4676 operates from a 4.5V to 26.5V input sup- ply and steps down VIN to two outputs ranging from 0.5V to 5.4V. Two outputs can current share to provide up to 26A (i.e., 13A + 13A as one output).
Digital power system management:
set, monitor, change and log power
Managing power and implementing flexibility in a high rail count circuit board can be challenging, requiring hands-on prob- ing with digital voltmeters and oscilloscopes, and often rework of PCB components. To simplify power management, espe- cially from a remote location, there is a trend to configure and monitor power via a digital communications bus. Digital power system management (PSM) enables on-demand telemetry capability to set, monitor, change and log power parameters.
Dual μModule regulator with precision READ/WRITE of power parameters
The LTM4676 is a dual 13A output constant frequency switching mode DC/DC μModule (micromodule) regu- lator (Figure 175.1). In addition to delivering power at a
Figure 175.1 • LTM4676: Dual 13A Output μModule Regulator with PMBus Interface Analog Circuit Design: Design Note Collection. http://dx.doi.org/10.1016/B978-0-12-800001-4.00175-7
Internal or external compensation
The LTM4676 offers both internal or external compensation, which can optimize the transient response over a wide oper- ating range. Figure 175.2 shows that the peak-to-peak output voltage is only 94mV with a 50% load step.
Current share for up to 100A at 1VOUT
The LTM4676 uses a constant frequency peak current mode control architecture, which offers a cycle-by-cycle cur- rent limit and easy current sharing among multiple phases.
Paralleling modules can achieve much higher output current capability. For example, four LTM4676 μModule regula- tors can be paralleled to provide up to 100A output current.
Figure 175.3 shows the thermal picture. With 300LFM of air- flow, the hot spot temperature rise is only 64.3°C. The even thermal distribution among modules is due to excellent cur- rent sharing performance. Figure 175.4 is a photo of the demo board with four LTM4676 μModule regulators assembled to provide 100A at 1V.
Conclusion
Linear Technology’s digital power system management (PSM) products provide users with critical power-related data. One can access load current, input current, output voltages, com- pute power consumption, efficiency, and access other power management parameters via a digital bus. This enables predic- tive analytics, minimizes operating costs, increases reliability and ensures smart energy management decisions can be made.
On-demand digital control and monitoring of system power with the LTM4676 eliminates PCB layout and cir- cuit component manipulation and accelerates system charac- terization, optimization and data mining during prototyping, deployment and field operation.
For demo kits, free download of the LTPowerPlay GUI and PSM training videos, please visit www.linear.com and type
“PSM” in the SEARCH box.
Figure 175.2 • Transient Response of the LTM4676 in Figure 175.1 at VIN= 12V, VOUT1= 1.8V, IO= 6.5A ∼ 13A
Figure 175.3 • Four LTM4676 Current Sharing: Thermal Picture at VIN= 12V, VOUT= 1.0V/100A, 300LFM Airflow
Figure 175.4 • Four LTM4676, Each in a 16mm × 16mm × 5.01mm LGA Package Deliver 100A at 1VOUT
176
Jaino Parasseril
36V input, low output noise, 5A
μModule regulator for precision data acquisition systems
The switching frequency can be adjusted between 200kHz and 1MHz with the RT resistor, or the SYNC pin can syn- chronize the internal oscillator to an external clock. The 5A current limit can be reduced by utilizing the IMAX pin. The PGOOD pin can be used to detect when the output voltage is within 10% of the target value.
PCB trace voltage compensation using SENSEP
The resistance of PCB traces between the μModule regula- tor and the load can result in voltage drops that cause a load regulation error at the point of load. As the output current increases, the voltage drop increases accordingly. To eliminate this voltage error, the LTM8028’s SENSEP pin can be con- nected directly to the load point.
Programmable output voltage
The output voltage can be digitally programmed in 50mV increments by controlling the LTM8028’s 3-state inputs:
VO0, VO1 and VO2. Additionally, the MARGA pin can be used for output margining via analog control that adjusts the output voltage by up to ±10%.
Introduction
Low output noise, fast transient response and high efficiency are just a few of the stringent power supply demands made by applications featuring high data rate FPGA I/O channels and high bit count data converters. The power supply designer faces the difficult task of meeting all of these requirements with as few components as possible, since no single topology easily meets all three.
For instance, high performance linear regulators achieve the required low output noise and fast transient response, but tend to dissipate more power than a switching topology, resulting in thermal issues. Switching regulators, on the other hand, are generally more efficient and run cooler than linear regulators, but generate significantly more output noise and cannot respond as quickly to transients. Power supply design- ers often resort to combining the two topologies, using a switching regulator to efficiently step down a relatively high bus voltage, followed by a linear post regulator to produce a low noise output. Although it is possible to produce a low noise supply in this way, it requires careful design to achieve high efficiency and fast transient response.
An easier way to reap the benefits of both a linear regula- tor and a switching regulator is to use the LTM8028, which achieves low noise, fast transient response and high efficiency by combining both regulators into a single part.
Integrated switching and linear regulators
The LTM8028 is a 36VIN, 5A μModule regulator that combines a synchronous switching converter and low noise linear regulator in a 15mm × 15mm × 4.92mm BGA package. It operates from an input range of 6V to 36V with an output voltage that can be programmed between 0.8V and 1.8V. The combination of the two converters results in tight tolerance of line and load regula- tion over the −40 °C to 125 °C temperature range.
Figure 176.1 • μModule Regulator Takes a Wide Ranging 6V to 36V Input and Produces a Low Noise 1.8V Output with Up to 5A Output Current
Analog Circuit Design: Design Note Collection. http://dx.doi.org/10.1016/B978-0-12-800001-4.00176-9
DC1738A highlights the LTM8028 capabilities
A 1.8V output application is shown in Figure 176.1. The LTM8028 comes in a 15mm × 15mm × 4.92mm BGA pack- age and is featured in the demonstration circuit DC1738A, shown in Figure 176.2.
Noise test comparison using LTC2185 ADC
When powering high speed analog-to-digital converters (ADCs), it is important to use a power supply that is as clean as possible. Any switching spurs that are present on the power supply rail will translate into AM modulation in the ADC output spectrum. The noise performance of the LTC2185, a 16-bit ADC, was evaluated to see the difference between using (1) a typical LDO, (2) a typical switching regulator, and (3) the LTM8028 low noise μModule regulator. A simplified schematic of the test is shown in Figure 176.3, where the DUT is represented by either of the configurations.
Figure 176.4 shows the FFT plots using the three different methods of powering the LTC2185 when sampling a 70MHz tone at 100Msps. The LDO provides a clean power supply, achieving a SINAD of 76.22dB. However, when powered by
a typical 250kHz switching regulator, there are spurs around the fundamental with an offset frequency of 250kHz. These are switching regulator spurs that are AM modulated around the carrier frequency. The sampling process produces 250kHz spurs at baseband. As a result, the SINAD drops to 71.84dB, around 4dB compared to an LDO. This reduces the LTC2185 to nearly 12-bit performance. In demanding applications where tenths of dBs are significant, losing 4dB of SINAD because of a noisy regulator is unacceptable. In addition to degrading the SINAD of the ADC, these spurs may land on neighboring channels or on other signals of interest, making it impossible to receive meaningful data from those channels.
With the LTM8028, only a few extraneous spurs exist near the desired frequency and the SINAD performance is only 0.03dB worse than the LDO baseline. The spurious content that was very pronounced in the spectrum of the switching regulator is virtually eliminated. As a result, there will not be any performance degradation of the LTC2185 when using a LTM8028 regulator.
Conclusion
The LTM8028 μModule regulator combines a linear regu- lator and a switching regulator to form a DC/DC converter with minimal power loss, low noise and UltraFast transient response, all in a 15mm × 15mm × 4.92mm BGA package.
Figure 176.2 • The LTM8028 Makes it Possible to Build a Minimal Component-Count Regulator that Meets Stringent Noise, Efficiency and Transient Response Requirements
Figure 176.3 • Noise Test Schematic Using Different Supplies to Power 16-Bit LTC2185 ADC
177
Alan Chern Jason Sekanina
Step-down μModule regulator produces 15A output from inputs down to 1.5V—no bias supply required
15A high efficiency output from a low input voltage
The LTM4611 is a switch mode, step-down DC/DC μModule regulator in a compact 15mm × 15mm × 4.32mm LGA surface mount package. The switching controller, MOS- FETs, inductor and supporting components are housed in the package. With a built-in differential remote sense amplifier, the LTM4611 can tightly regulate its output voltage from 0.8V to within 300mV of VIN and deliver 15A output effi- ciently from 1.5V to 5.5V input.
Only a handful of components are needed to create a com- plete point-of-load (POL) solution with the LTM4611 (see Figure 177.1). The CSS capacitor provides smooth start-up on the output and limits the input surge current during power- up. CFF and CP set the loop-compensation for fast transient response and good stability. The output voltage, 1.5V, is set by a single resistor, RSET.
Efficiency is exceptional, even down to the lowest input voltages, as shown in Figure 177.2.
Input and output ripple
Output capacitors should have low ESR to meet output voltage ripple and transient requirements. A mixture of low ESR poly- mer and/or ceramic capacitors is sufficient for producing low output ripple with minimal noise and spiking. Output capacitors
1.5V to 5.5V input, 0.8V to 5V output from a 15mm × 15mm × 4.32mm LGA package
Figure 177.1 • 1.8VIN to 5.5VIN to 1.5VOUT with 15A Output Load Current
Figure 177.2 • Efficiency of Figure 177.1 Circuit
Analog Circuit Design: Design Note Collection. http://dx.doi.org/10.1016/B978-0-12-800001-4.00177-0
are chosen to optimize transient load response and loop stability to meet the application load-step requirements by using the Excel-based LTpowerCAD design tool. (Table 5 of the LTM4611 data sheet provides guidance for applications with 7.5A load- steps and 1μs transition times.) For this design example, four 100μF ceramic capacitors are used. Figures 177.3 and 177.4 show input and output ripple at 15A load with 20MHz band- width-limit. View the associated videos to see the test methodol- ogy, as well as ripple waveforms without bandwidth limiting.
For this design, the choice of input capacitors is critical due to the low input voltage range. Long input traces can cause voltage drops, which could nuisance-trip the μModule regula- tor’s undervoltage lockout (UVLO) detection circuitry. Input ripple, typically a non-issue with higher input voltages, may fall a significant percentage below nominal—close to UVLO—at lower input voltages. In this case, input voltage ripple should be addressed since input filter oscillations can occur due to poor
dissipation with or without air flow. Figure 177.5 shows the top view thermal imaging of the LTM4611 at a power loss of 3.5W with no air flow, when converting 5V to 1.5V.
Internal self-heating of the LTM4611 remains quite low even at a low 1.8V input voltage due to its micropower bias generator that enables strong gate drive for its power MOS- FETs. Figure 177.6 shows a power loss of 3.2W with hot spots slightly changed from their positions with a 5V input—the nominal surface temperature is 60°C. Watch the associated videos to see the test set-up and watch 200 LFM of air flow cool the unit by 10°C.
Figure 177.3 • 5VIN to 1.5VOUT at 15A Output Load
Figure 177.4 • 1.8VIN to 1.5VOUT at 15A Output Load
Figure 177.5 • 5VIN to 1.5VOUT at 15A Output Load.
3.5W Power Loss with 0LFM and 65°C Surface Temperature Hot Spot
Figure 177.6 • 1.8VIN to 1.5VOUT at 15A Output Load. 3.2W Power Loss with 0LFM and 65°C Surface Temperature Hot Spot
178
Alan Chern
Dual μModule DC/DC regulator
produces high efficiency 4A outputs from a 4.5V to 26.5V input
These regulators are designed to eliminate layout errors and to offer a ready-made complete solution. Only a few external components are needed since the switching controllers, power MOSFETs, inductors, compensation and other support com- ponents are all integrated within the compact surface mount 15mm × 15mm × 2.82mm LGA package. Such easy layout saves board space and design time by implementing high den- sity point-of-load regulators (Figure 178.1).
The LTM4619 switching DC/DC μModule converter regulates two 4A outputs from a single wide 4.5V to 26.5V input voltage range. Each output can be set between 0.8V and 5V with a single resistor. In fact, only a few components are needed to build a complete circuit (see Figure 178.2).
Figure 178.2 shows the LTM4619 μModule regulator in an application with 3.3V and 1.2V outputs. The output voltages can be adjusted with a value change in RSET1 and RSET2. Thus, the final design requires nothing more than a few resistors and capacitors. Flexibility is achieved by pairing outputs, allowing the regulator to form different combinations such as single input/dual independent outputs or single input/parallel single output for higher maximum current output.
The efficiency of the system design for Figure 178.2 is shown in Figure 178.3 and power loss is shown in Figure 178.4, both at various input voltages. Efficiency at light
Dual system-in-a-package regulator
Systems and PC boards that use FPGAs and ASICs are often very densely populated with components and ICs. This dense real estate (especially the supporting circuitry for FPGAs, such as DC/DC regulators) puts a burden on system designers who aim to simplify layout, improve performance and reduce component count. A new family of DC/DC μModule regula- tor systems with multiple outputs is designed to dramatically reduce the number of components and their associated costs.
Figure 178.1 • The LTM4619 LGA Package is Only
15mm × 15mm × 2.82mm and Houses Dual DC/DC Switching Circuitry, Inductors, MOSFETs and Support Components
Figure 178.2 • 4.5 V to 26.5V Input to Dual 3.3V and 1.2V Outputs with 4A Maximum Output Current Each Analog Circuit Design: Design Note Collection. http://dx.doi.org/10.1016/B978-0-12-800001-4.00178-2
load operation can be improved with selective pulse-skipping mode or Burst Mode operation by tying the mode pin high or leaving it floating.
Multiphase operation for four or more outputs
For a 4-phase, 4-rail output voltage system, use two LTM4619s and drive their MODE_PLLIN pins with a LTC6908-2 oscillator, such that the two μModule devices are synchronized 90° out of phase. Reference Figure 21 in the LTM4619 data sheet. Synchronization also lowers voltage rip- ple, reducing the need for high voltage capacitors whose bulk size consumes board space. The design delivers four differ- ent output voltage rails (5V, 3.3V, 2.5V and 1.8V) all with 4A maximum load.
Thermal performance
Exceptional thermal performance is shown in Figure 178.5 where the unit is operating in parallel output mode; single 12VIN to a single 1.5VOUT at 8A. Both outputs tied together create a combined output current of 8A with both channels running at full load (4A each). Heat dissipation is even and minimal, yielding good thermal results. If additional cooling is needed, add a heat sink on top of the part or use a metal chas- sis to draw heat away.
Conclusion
The LTM4619 dual output μModule regulator makes it easy to convert a wide input voltage range (4.5V to 26.5V) to two or more 4A output voltage rails (0.8V to 5V) with high effi- ciency and good thermal dissipation. Simplicity and perfor- mance are achieved through dual output voltage regulation from a single package, making the LTM4619 an easy choice for system designs needing multiple voltage rails.
Figure 178.3 • Efficiency of the Circuit in Figure 178.2 at
Different Input Voltage Ranges for 3.3V and 1.2V Outputs Figure 178.4 • Power Loss of the Circuit in Figure 178.2 at Different Input Voltages for 3.3V and 1.2V Outputs
179
Eddie Beville Alan Chern
Triple output DC/DC μModule
regulator in 15mm × 15mm × 2.8mm surface mount package replaces up to 30 discrete components
The two switching regulators, operating at a 1.25MHz switching frequency, accept input voltages between 2.35V to 5.5V and each delivers a resistor-set output voltage of 0.8V to 5V at 4A of continuous current (5A peak). The output voltages can track each other or another voltage source. Other features include, low output voltage ripple and low thermal dissipation.
The VLDO regulator input voltage (1.14V to 3.5V) is capable of up to 1.5A of output current with an adjustable output range of 0.4V to 2.6V, also via a resistor. The VLDO regulator has a low voltage dropout of 200mV at maximum load. The regulator can be used independently, or in conjunc- tion with either of the two switching regulators to create a high efficiency, low noise, large-ratio step-down supply—
simply tie one of the switching regulator’s outputs to the input of the VLDO regulator.
Multiple low noise outputs
The LTM4615 is capable of operating with all three regulators at full load while maintaining optimum efficiency. A typical LTM4615 design (Figure 179.2) for a 3.3V input to three out- puts has the VLDO input driven by VOUT2. The efficiency of this design is shown in Figure 179.3.
Introduction
When space and design-time are tight in multivoltage systems, the solution is a multioutput DC/DC regulator IC. For more space and time constraint systems, a better solution is an already-fabricated compact multioutput DC/DC system that includes not only the regulator ICs but the supporting compo- nents such as the inductors, compensation circuits, capacitors and resistors.
Dual switching 4A and 1.5A VLDO regulators
The LTM4615 offers three separate power supply regulators in a 15mm × 15mm × 2.8mm LGA surface mount package:
two switching DC/DC regulators and one very low dropout VLDO linear regulator (Figure 179.1). MOSFETs, inductors, and other support components are all built in. Each power supply can be powered individually or together, to form a single input, three output design. Moreover, for an other- wise complex triple output circuit design, the task is eased to designing with only one device while the layout is as simple as copying and pasting the LTM4615’s package layout. One LTM4615 replaces up to 30 discrete components when com- pared to a triple-output high efficiency DC/DC circuit.
Figure 179.1 • Three DC/DC Circuits in One Package Figure 179.2 • Triple Output LTM4615: 3.3V Input, 1.8V (4A), 1.2V (4A), 1.0V (1.5A)
Analog Circuit Design: Design Note Collection. http://dx.doi.org/10.1016/B978-0-12-800001-4.00179-4