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ADALM-SR1 hardware

This page is for the released revision of the ADALM-SR1. Documentation for the pilot run (rev A) is here for reference: ADALM-SR1 hardware

Description

The ADALM-SR1 (Analog Devices Active Learning Module, Switching Regulator #1) board is a companion module for several switching regulator exercises covering buck and boost regulators:

Activity: Boost and Buck converter elements and open-loop operation
Activity: Buck Converters: closed loop operation
Activity: Boost Converters: closed loop operation

The circuits required for these exercises exceed the complexity that can be constructed on a breadboard, so the ADALM-SR1 is required to run them, although the simulations can be run beforehand to gain insight into the circuits' operation.

The Figures 1a and 1b show an overview of the board, along with connections to an ADALM2000 (m2k) and meters.

Figure 1a. ADSRALM overview


Figure 1b. ADSRALM overview

ADALM-SR1 Jumpers and Connections

The ADALM-SR1 uses 0.635mm (0.025-mil) headers for configuration jumpers, signal inputs, and signal outputs. Signal inputs and outputs are 2-conductor headers with 5.08mm (200-mil) pitch so that they cannot be confused with configuration jumpers. The lower conductor is always a ground connection (that is not always used) and an arrow indicates whether the upper conductor is an input or output.


Figure 2. Topology, Mode selection, and Loads

Inductance Selection

A Wurth 749196141 6-winding coupled inductor is used in both boost and buck configurations. The datasheet inductance for a single winding is 8.5μH, with a DC resistance of 344 milliohms. The windings are connected in series on the ADALM-SR1, allowing the inductance to be changed as noted in the table below. (Values in the table are measured from a typical board.)

Inductance Selection (P3)
Jumper
Position EXT IND 1 TAP 2 TAPS 3 TAPS 4 TAPS 5 TAPS 6 TAPS
Function Ext. inductor at TP3, TP4 7.7μH inductance 31.5μH inductance 72.6μH inductance 131.5μH inductance 216.2μH inductance 313.4μH inductance



Output Capacitors Selection

A 4.7μF capacitor is always connected to the output of the circuit. An additional 47μF and 470μF can be added by installing jumpers according to the table below.

Output Capacitors Selection
Jumper P8, P11
Position Installed Open
Function P8 connect aditional 47μF capacitance No additional capacitance
P11 connect aditional 470μF capacitance No additional capacitance



Load Resistors Selection

A resistive load may be connected to the output of the circuit. Resistances range from 12.5Ω to 200Ω, and may be added in parallel according to the table below. The jumpers are 3-position, with the righ-hand position connecting the resistor to ground, and the left-hand position allowing the effective resistance to be adjusted by Pulse-width-modulating the ground connection.

Load Resistors Selection
Jumper P18, P14, P13, P17, P16, P15
Position Installed Open
Function P18 connect 200 Ω load resistance No aditional load resistor connected
P14 connect 200 Ω load resistance No aditional load resistor connected
P13 connect 100 Ω load resistance No aditional load resistor connected
P17 connect 50 Ω load resistance No aditional load resistor connected
P16 connect 25 Ω load resistance No aditional load resistor connected
P15 connect 12.5 Ω load resistance No aditional load resistor connected
Notes 7V max across 25Ω, 12.5Ω resistors will turn on the Over Power LED illuminates as warning.


The R87 (LOAD CONTROL) potentiometer controls the duty cycle of all load resistors whose jumper is placed in the adjustable position, by swithcing the ground connection. (YES this is super weird, but it's convenient and it works much better than you'd think!) Duty cycle is guaranteed to be zero when fully counter-clockwise and 100% when fully clockwise. Thus the load can be a combination of fixed and variable resistances, and the exact duty cycle of the onboard PWM circuit can be measured at P40. The signal at P40 has a 1k impedance and maybe overdriven by a 3.3V logic signal, allowing the load to be stepped.
The load PWM frequency is fixed at 200kHz, approximately 10x the typical operating frequency of most experiments, thus appearing as a steady (DC) load.
A 0.1 ohm current sense resistor is in the ground return of the load resistors, allowing the total load current to be easily measured with meter set to the 200mV range at either the LOAD turret post (TP25) or the LOAD CURRENT jumper (P39).

Topology, FET and Current Sense Selection

The selection between boost or buck topologies is made by jumpers P25, P35, and P37.

FET Selection Current Sense Selection
Jumper P37 P35 P25
Position BUCK BOOST BUCK BOOST HIGH LOW
Function Select buck topology Select boost topology Select the proper FET for buck topology Select the proper FET for boost topology Used for buck topology Used for boost topology
Notes Proper selection allows complete inductor waveform to be viewed.


In the boost configuration, P37 does not bypass Schottky diode D4, P35 routes the FET driver control to the low-side switch, and P25 selects the high-side current sense amplifier.
In the buck configuration, P37 bypasses D4, P35 routes the FET driver control to the high-side switch, and P24 selects the low-side current sense amplifier.

Close inspection of the operation of the circuit will show that in theory, either current sense amplifier will work for both topologies, but the amplifier that is NOT at the switch node is chose in order to minimize errors due to common-mode excursion.



Mode Selection

The ADALM-SR1 has several operational modes, set by the jumpers noted below.

The MODE jumper selects between peak current mode and duty cycle control:

  • Peak Current: A fixed frequency clock starts the inductor current ramp by turning on a MOSFET switch, and the switch is opened when a peak current is reached.
  • Duty Cycle: The duty cycle of the MOSFET switch is controlled directly.


Control Mode Selection
Jumper P32
Position Peak Current Duty Cycle
Function Start on clock rising edge, stop on peak current Direct duty cycle control
Notes Closed/open-loop determined by Duty Cycle or Current Threshold jumper.


The peak current circuit is always active, even in duty-cycle mode; increasing robustness in the event of an output short circuit.


Duty Cycle Source Selection

An LTC6992 Pulse-Width Modulator allows the switching MOSFET's duty cycle to be controlled directly, either manually by adjusting the DUTY CYCLE knob, or under the control of the error amplifier.

Duty Cycle Source Selection
Jumper P23
Position Closed-loop Manual
Function Duty controlled by error amplifier Duty controlled by potentiometer
Notes Current Threshold still operational for safety, determined by Current Threshold Potentiometer.



Current Threshold Source Selection

In peak-current control modes, the peak current can be controlled either manually by adjusting the CURRENT THRESHOLD knob, or under the control of the error amplifier. The current threshold is also always active in voltage control modes, maintaining per-cycle current limit as an added safety and robustness feature.

Current Threshold Source Selection
Jumper P22
Position Manual Closed-loop
Function Threshold controlled by potentiometer Threshold controlled by error amplifier
Notes Set Duty Cycle pot to approx. 50%. (not critical, rising edge controls start of the ramp)



Feedback Selection

Three options for feedback network are provided, assuming a 1.25V reference voltage. The 5V option is usually used for buck experiments (input voltage greater than 5V), and the 12V option is usually used for boost experiments (input less than 12V). Footprints for optional 0603-sized resistors are included for user-defined feedback networks, selected by the third jumper option.

Feedback Selection
Jumper P20
Position 5V 12V ALT
Function Usually used for buck topology Usually used for boost topology Select user-installed feedback resistors



Signal Measurement and Injection Points

The ADALM-SR1 provides numerous test points for stimulating (modulating) and measuring the operation of the circuit, such as input and output voltage, inductor current, and output current. Several aspects of the circuit's dynamic response can also be measured:
* In open-loop voltage mode, modulate the duty cycle control voltage to characterize the response of the power stage * In open-loop current mode, modulate the current threshold (ITH) to characterize the response of the power stage * In any closed-loop mode, modulate the feedback divider to characterize the closed-loop response of the whole circuit.
Connections are summarized in Figure X below, and the following tables.

Measurement Points
Name Notes
TP1 P_PROT Overvoltage/overcurrent protected power.
P1 SW_NODE_HI Switch node in buck topology.
P4 SW_NODE_LOW Switch node in boost topology.
P2 IHIGH Current sense amplifier output, boost configurations (0.1Ω sense R, G=7, 1.429A/V net output).
P12 ILOW Current sense amplifier output, buck configurations (0.1Ω sense R, G=7, 1.429A/V net output).
P10, P9, TP5, TP7 V_OUT Experiment output voltage. P10 can be AC coupled by removing P9.
P5 FB_MEAS Feedback perturbation measurement (AC coupled).
P33 CLOCK Master clock, 3.3V logic level.
P34 GATE CONTROL FET gate control signal, 3.3V logic level.
Injection Points
Name Notes
P28 ITH MOD Peak current control modulation (1.429A/V). Install P29 to DC couple.
P27 DUTY CYCLE MOD Duty Cycle modulation (100%/V). Install P26 to DC couple.
P7 FB_MOD Feedback modulation for loop gain measurements (XXV/V). Install P6 to DC couple.

Hardware Setup Procedure

Refer to individual lab exercises for detailed setup information.

Auxiliary Circuit Details

The setup and operation of circuitry associated with the lab exercises is described in detail in the exercises themselves. The ADALM-SR1 includes various auxiliary housekeeping and protection circuits described here.



Housekeeping supplies and reference

The ADALM-SR1 has two power inputs. The experiment power input is supplied by the user, and the voltage will vary depending on the experiment being run. An additional micro USB connector is the input for a 5V “housekeeping” supply that powers all of the control circuitry, allowing the experiment power to vary over a wide range. An LT3472 boosts / inverts the 5V supply to +15 / -2V, respectively. This provides a high voltage and slightly negative voltage for the LT1995 current sense amplifiers, and a negative supply for the error amplifier.
An LT1970-1.25 provides an accurate reference for the error amplifier and duty cycle, current threshold adjustment potentiometers.

Input Overvoltage, Undervoltage, Reverse voltage, and Overcurrent

The Figure below shows an LTspice schematic of the ADALM-SR1's protection circuitry. The simulation file is available at OL_engineer_proofing.asc and running the simulation in LTspice will exercise some of the various fault conditions.

An LTC4368 and associated circuitry protects the experiment power input by only turning on when the supply is between 3V and 15V. The circuit is protected from voltages between -40V and +60V. The LTC4368 also functions as a fuse, shutting off the supply if the current exceeds 2A.

Output Overvoltage

In boost mode, the ADSRALM can produce high voltages under certain conditions: if the duty cycle is high and the load is light, or if feedback is disconnected. An LTC2912 overvoltage / undervoltage supervisor will disable the switching circuitry if the output exceeds 22V. An SMAJ24A, 24-volt TVS diode provides additional protection.

Inductor, Load Resistor Overtemperature

The inductor and onboard load resistors can get warm during certain experiments or if the board is misconfigured. Three temperature sensors measure the inductor temperature and the temperature of the high-dissipation areas of the load resistor bank. If any temperature exceeds 60ºC, switching is disabled for a 1.9 second cool-down period.
The low-resistance loads consist of parallel, single 100Ω, 1/2W resistors - An orange LED near the associated jumpers illuminates when the output voltage exceeds 7V as a warning that these must be disconnected.
The high resistance loads consist of multiples of two 100-ohm, 1/4W resistors in series, which will handle voltages up to 14V. A temperature sensor is still included in case the output voltage exceeds 14V or if the experiment is left running for an extended period of time.

Schematic, PCB Layout, Bill of Materials

ADALM-SR1 Design & Integration Files

End of Document

university/tools/lab_hw/adalm-sr1.1608081122.txt.gz · Last modified: 16 Dec 2020 02:12 by Mark Thoren