Analog Devices EVAL-LTM4682-A1Z Evaluation Board User Guide

General Description

The EVAL-LTM4682-A1Z evaluation board features the LTM4682, a wide input and output voltage range, high efficiency, and power density, quad output PolyPhase® DC-to-DC step-down µModule® (micromodule) power regulator with digital power system management (PSM). The EVAL-LTM4682-A1Z evaluation board is configured as a 4-phase, four-output device. A similar evaluation board with a 4-phase, single-output configuration is also available (EVAL-LTM4682-A2Z).

The EVAL-LTM4682-A1Z evaluation board's default input voltage range is 4.5V to 16V. However, if VIN is lower than 6V and within 4.5V ≤ VIN ≤ 5.75V, a minor modification to certain existing on-board components is required. Refer to step 8 (Operation at Low VIN: 4.5V ≤ VIN ≤ 5.75V) in the Procedure section.

The factory default output voltage VOUT [0:3] is 0.7V at 31.25A maximum load current per channel. Each channel can deliver up to 31.25A maximum load current, but forced airflow and heatsink might also be used to further optimize the output power when all output rails are on and fully loaded. The evaluation board output voltages can be adjusted from 0.7V up to 1.35V. Refer to the LTM4682 data sheet for thermal derating curves and recommended switching frequency when adjusting the output voltage.

The factory default switching frequency is preset at 575kHz (typical). The EVAL-LTM4682-A1Z evaluation board comes with a PMBus interface and digital PSM functions. An on-board 12-pin connector is available for users to connect the dongle DC1613A to the evaluation board, which provides an easy way to communicate and program the part using the LTpowerPlay® software development tool.

The LTpowerPlay software and the I2C/PMBus/SMBus dongle DC1613A allow users to monitor real-time telemetry of input and output voltages, input and output current, switching frequency, internal IC die temperatures, external power component temperatures, and fault logs. Programmable parameters include device address, output voltages, control loop compensation, switching frequency, phase interleaving, discontinuous-conduction mode (DCM) or continuous-conduction mode (CCM) of operation, digital soft start, sequencing, and time-based shutdown, fault responses to input and output overvoltage, output overcurrent, IC die and power component over-temperatures.

The LTM4682 is available in a thermally enhanced, low-profile 330-pin (15mm × 22mm × 5.71mm) BGA package. It is recommended to read the LTM4682 data sheet and this user guide prior to using or making any hardware changes to the EVAL-LTM4682-A1Z evaluation board.

Ordering Information appears at the end of the data sheet.

Evaluation Board Photo

Figure 1 shows the EVAL-LTM4682-A1Z evaluation board. The part marking is either an ink mark or a laser mark.

Performance Summary

Specifications are at TA = 25°C.

Features and Benefits

• Quad digitally adjustable analog loops with a digital interface for control and monitoring.
• Optimized for low output voltage ranges and fast load transient response.
• 15mm x 22mm × 5.71mm Ball grid array (BGA) package.

EVAL-LTM4682-A1Z Evaluation Board

Quick Start

Required Equipment

• One power supply that can deliver 20V at 20A.
• Four electronic loads that can deliver 35A at 0.7V each load.
• Five digital multimeters (DMMs).

Procedure

The EVAL-LTM4682-A1Z evaluation board is easy to set up to evaluate the performance of the LTM4682. See Figure 2 for proper measurement equipment setup and use the following test procedures.

Figure 2. Proper Measurement Equipment Setup

1. With power off, connect the input power supply between VIN (TP9) and GND (TP10). Set the input voltage supply to 0V.

2. Connect the first load between VOUT0 (TP23) and GND (TP24), connect the second load between VOUT1 (TP20) and GND (TP21), connect the third load between VOUT2 (TP7) and GND (TP8), connect the fourth load between VOUT3 (TP5) and GND (TP6). Preset all the loads to 0A.

3. Connect the DMM between the input test points: VIN (TP1) and GND (TP11) to monitor the input voltage. Connect DMMs between VOUT0+ (TP16) and VOUT0– (TP17), VOUT1+ (TP18) and VOUT1– (TP19), VOUT2+ (TP12) and VOUT2– (TP14), VOUT3+ (TP13) and VOUT3– (TP15) to monitor the corresponding DC output voltages of Channel 0, Channel 1, Channel 2, and Channel 3. These output voltage test points are Kelvin sensed directly across COUT2 (Channel 0), COUT10 (Channel 1), COUT20 (Channel 2), and COUT29 (Channel 3) to provide an accurate measurement of output voltages. Do not apply load current to any of the above test points to avoid damage to the regulator. Do not connect the scope probe ground leads to VOUT0−, VOUT1–, VOUT2−, and VOUT3-.

4. Prior to powering up the EVAL-LTM4682-A1Z, check the default position of the jumpers and switches in the following positions.

5. Turn on the power supply at the input. Slowly increasing the input voltage from 0V to 12V (typical). Measure and ensure the input supply voltage is 12V and flip SWR0 (RUN0) and SWR1 (RUN1), SWR2 (RUN2), and SWR3 (RUN3) to the ON position. The output voltages should be 0.7V ±0.5% (typical) for VOUT0, VOUT1, VOUT2, and VOUT3.

6. Once the input and output voltages are properly established, adjust the input voltage between 6V to 14V max and the load current within the operating range of 0A to 31.25A max per channel. Observe the output voltage regulation, output voltage ripples, switching node waveform, load transient response, and other parameters. See Figure 3 for proper output voltage ripple measurement.

To measure the input/output voltage ripples properly, do not use the long ground lead on the oscilloscope probe. See Figure 3 for the proper scope probe technique. Short, stiff leads need to be soldered to the (+) and (-) terminals of an input or output capacitor. The probe's ground ring needs to touch the (-) lead, and the probe tip needs to touch the (+) lead.

The output voltage ripples of Channel 0, Channel 1, Channel 2, and Channel 3 can also be monitored using on-board BNC terminals. Connect short BNC cables from VOUT0 (J3), VOUT1 (J4), VOUT2 (J5), and VOUT3 (J6) to the inputs of a 4-channel oscilloscope (scope probe ratio 1:1, AC-coupling) to observe output voltage ripples.

Figure 3. Scope Probe Placement for Measuring Output Ripple Voltage

(Option) Operation with VBIAS

7. The VBIAS pin is the 5.5V output of an internal buck regulator that can be enabled or disabled with RUNP. The VBIAS regulator input is the VIN_VBIAS pin and is powered by VIN. The advantage of using VBIAS is bypassing the internal INTVCC_LDO powered from VIN, turning on the internal switch connected to the 5.5V VBIAS to INTVCC_01 and INTVCC_23 of the part, therefore, reducing the power loss, improving the overall efficiency, and lowering the temperature rise of the part when operating at high VIN and high switching frequency. The VBIAS must exceed 4.8V, and the VIN must be greater than 7V to activate the internal switch connecting VBIAS to INTVCC_01 and INTVCC_23 of the part. In typical applications, it is recommended that VBIAS is enabled.

Operation at Low VIN: 4.5V ≤ VIN ≤ 5.75V

8. Remove R31 to disconnect VIN_VBIAS from VIN. Remove C25. Set RUNP (P1) to the OFF position. Tie SVIN_01 to INTVCC_01 by stuffing R142 with a 0Ω resistor. Tie SVIN_23 to INTVCC_23 by stuffing R143 with a 0Ω resistor. Make sure VIN is within 4.5V ≤ VIN ≤ 5.75V. Additional input electrolytic capacitors may be installed between VIN (TP9) and GND (TP10) to prevent VIN from drooping or overshoot to a voltage level that can exceed the specified minimum VIN (4.5V) and maximum VIN (5.75V) during large output load transient.

(Option) On-Board Load Step Circuit

9. The EVAL-LTM4682-A1Z evaluation board provides an on-board load transient circuit to measure ΔVOUT peak-to-peak deviation during rising or falling dynamic load transient. The simple load step circuit consists of two paralleled 40V N-channel power MOSFETs in series with two paralleled 10mΩ, 2W, 1% current sense resistors. The MOSFETS are configured as voltage control current source (VCCs) devices; therefore, the output current step and its magnitude are created and controlled by adjusting the amplitude of the applied input voltage step at the gate of the MOSFETs. A function generator provides a voltage pulse between IOSTEP_CLK01 (TP22) and GND (TP2). The input voltage pulse should be set at a pulse width of less than 300µs and a maximum duty cycle of less than 2% to avoid excessive thermal stress on the MOSFET devices. The output current step is measured directly across the current sense resistors and monitored by connecting the BNC cable from IOSTEP_01 (J1) to the oscilloscope's input (scope probe ratio 1:1, DC-coupling). The equivalent voltage to the current scale is 5mV/1A. The load step current slew rate di/dt can be varied by adjusting the rise time and fall time of the input voltage pulse. The load step circuit of Channel 0 or Channel 1 is connected to VOUT0 by default but can be used for VOUT1 by simply removing the 0Ω jumper R92 and stuffing it at the position of R93 and vice versa. Only one resistor, R92 or R93, can be stuffed at a time to avoid shorting VOUT0 and VOUT1 together. Repeat step 9 to perform load step transient evaluation for the VOUT1 rail. Similarly, load step transient evaluation of VOUT2 or VOUT3 can be performed using the same method described above. See the Schematics section for more details.

Connecting a PC to the EVAL-LTM4682-A1Z

Use a PC to reconfigure the digital power system management (PSM) features of the LTM4682, such as nominal VOUT, margin set points, overvoltage/undervoltage limits, output current and temperature fault limits, sequencing parameters, the fault logs, fault responses, GPIOs, and other functionality. The DC1613A dongle can be hot-plugged when VIN is present. See Figure 4 for the proper setup of the evaluation board.

Figure 4. EVAL-LTM4682-A1Z Evaluation Board Setup with a PC

LTpowerPlay Quick Start Guide

The LTpowerPlay is a powerful Windows-based development environment that supports Analog Devices digital power system management (PSM) ICs. The software supports a variety of different tasks. Use the LTpowerPlay to evaluate Analog Devices digital PSM µModule devices by connecting to an evaluation board system.

The LTpowerPlay can also be used in an offline mode (with no hardware present) to build a multichip configuration file that can be saved and reloaded anytime.

The LTpowerPlay provides unprecedented diagnostic tools and debug features. It becomes a valuable diagnostic tool during board bring-up to program or tweak the power management scheme in a system, or to diagnose power issues when bringing up rails.

The LTpowerPlay utilizes the DC1613A, USB-to-PMBus controller, to communicate with one of the many potential targets, including all the parts in the PSM product category evaluation system. The software also provides an automatic update feature to keep it current with the latest set of device drivers and documentation. Download and install the LTpowerPlay software at LTpowerPlay.

To access technical support documents for Analog Devices digital PSM products, visit the LTpowerPlay Help menu. Online help is also available through the LTpowerPlay interface.

Figure 5. LTpowerPlay Main Interface

LTpowerPlay Procedure

Use the following procedure to monitor and change the settings for the LTM4682.

1. Launch the LTpowerPlay GUI. The GUI should automatically identify the EVAL-LTM4682-A1Z (see the following system tree).

2. A green message box shows for a few seconds in the lower left-hand corner, confirming that LTM4682 is communicating.

NOTE: It is recommended that you press the 'Read All Registers' button in the toolbar to read settings from the hardware into the GUI.

3. In the Toolbar, Click the R (RAM to PC) icon to read the RAM from the LTM4682. The configuration is read from the LTM4682 and loaded into the GUI.

4. Example of programming the output voltage to a different value. In the Config Tab, Click on the Voltage tab in the main menu bar, and type in 1V in the VOUT_COMMAND box as shown in the following figure.

5. Then, Click the W (PC to RAM) icon to write these register values to the LTM4682.

6. The output voltage will change to 1V. If the write command is successfully executed, the following message should be seen.

7. All user configurations or changes can be saved in to the NVM. In the Toolbar, Click the RAM to NVM icon.

8. Save the evaluation board configuration to a (*.proj) file. Click the Save icon and save the file with a preferred file name.

Typical Performance Characteristics

Figure 6. Efficiency vs. Load Current

Figure 7. Thermal Performance

Figure 8. Load Transient Response

Figure 9. Output Ripple Voltage

EVAL-LTM4682-A1Z Evaluation Board Bill of Materials

This section lists the required circuit components for the EVAL-LTM4682-A1Z evaluation board.

EVAL-LTM4682-A1Z Schematics

The schematics for the EVAL-LTM4682-A1Z evaluation board are provided, detailing the circuit configurations for the LTM4682 µModule regulator.

*ASSEMBLY OPTION TABLE

Ordering Information

Revision History

Notes

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