ALLEGRO A81805 Evaluation Board User Guide
- May 15, 2024
- ALLEGRO
Table of Contents
ALLEGRO A81805 Evaluation Board
A81805 Evaluation Board User Guide
DESCRIPTION
The A81805 Evaluation Board is designed to aid system designers with evaluating the operation and performance of the A81805 and A81805-1 2.5 A synchronous buck regulators. The A81805 Evaluation Board is a PCB that is available in two configurations: the A81805 with VOUT of 3.3 V, and theA81805-1 with VOUT of 5.0 V. The evaluation board will arrive with a mark on one of the two silkscreen boxes at the top right identifying the device for which the evaluation board is configured.
FEATURES
Evaluation Board/Kit Features Text
EVALUATION BOARD CONTENTS
- A81805 Evaluation Board
- A81805-1 Evaluation Board
Table 1: A810805 Evaluation Board Configurations
Configuration Name| Part Number| V OUT| f SW|
I OUT Max
---|---|---|---|---
A81805 Version Evaluation Board| APEK81805KES-01- [MH or T]| 3.3 V| 2.2
MHz| 2.5 A
A81805-1 Version Evaluation Board| APEK81805KES-01- [MH or T]- 1| 5.0 V| 400
kHz| 2.5 A
Table 2: General Specifications
| Specification | Min | Nom | Max | Units |
|---|---|---|---|---|
| Absolute Maximum VIN Pin Voltage | –0.3 | – | 40 | V |
| Absolute Maximum EN Pin Voltage | –0.3 | – | 40 | V |
| Absolute Maximum SYNC Pin Voltage | –0.3 | – | 5.5 | V |
| Operating Input Voltage Range | 3.5 | – | 36 | V |
| Output Voltage – A81805 Version Evaluation Board | – | 3.3 | – | V |
| Output Voltage – A81805-1 Version Evaluation Board | – | 5.0 | – | V |
| Maximum Output Current | – | 2.5 | – | A |
| Synchronous Frequency Range | 0.4 | – | 2.5 | MHz |
USING THE EVALUATION BOARD
This section provides instructions on proper setup and a basic overview of the configuration options and features of the evaluation board. The A81805 datasheet contains detailed information on the use and functionality of each IC pin and should be used in conjunction with this user guide.
Figure 2: A81805 Evaluation Board Connections
Startup Procedure
Consult Figure 2 for details on interfacing hardware with the evaluation board. For more details on the evaluation board input and output connections, consult the Evaluation Board Inputs and Outputs section below.
For operation at lowest possible input voltage:
Step 1: Connect a suitable DC power supply to the VFIL and GND terminals.
A suitable power supply will be able to provide the desired input voltage
while sourcing a DC current of at least 3 A. Use caution to avoid reversing
the polarity when hooking up. Reversing the polarity on VFIL will result in a
condition that exceeds VIN absolute maximum ratings and will likely damage the
converter.
Step 2: Connect the desired load to the VOUT and GND terminals. If an
active electronic load is used, it may be necessary to apply the load after
Step 4 to ensure proper operation of the active load.
Step 3: Set the ENABLE jumper to “ON” for converter operation at minimum
input voltage or leave OPEN to use the accurate
enable functionality.
Step 4: Increase the voltage at VFIL to 10 V. Verify that the output voltage is approximately:
- 3.3 V for A81805 Version Evaluation Board
- 5.0 V for A81805-1 Version Evaluation Board
The converter is now running. At this point, VIN can be adjusted as desired. The maximum operating input voltage range is 36 V. The minimum operating input voltage is dependent upon the ENABLE jumper setting and the accurate enable resistor divider.
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
EVALUATION BOARD INPUTS AND OUTPUTS
Power Input
Connect a power supply using banana cables to the VFIL and GND through-hole banana jacks or with other suitable test leads to the VFIL and GND test points. VFIL is the power input to the board before the simple L-C input filter. Optionally, the VIN test point can be used to apply power directly to the VIN pin of the converter.
Power Output
Both versions of the evaluation board are capable of supplying 2.5 A of output current. For 2.5 A of continuous output current, a minimum input voltage of approximately 6.5 V for the A81805 Version Evaluation Board and approximately 7 V for the 81805-1 Version Evaluation Board is required. For consistent, stable converter operation, ensure the power supply can source 3 A of continuous current to the input of the evaluation board.
Switching Frequency and SYNC Input
Both the A81805 and A81805-1 have an internal oscillator that can generate the switching frequency. Additionally, they both have the capability of running from an external SYNC signal. If external synchronization is desired, a clock pulse can be applied to the SYNC test point on the evaluation board. However, erratic operation may occur if the FSET resistor (R1) is such that it sets the internal oscillator to a significantly different frequency than the externally applied synchronization signal. If external synchronization is desired, consult the datasheet for additional details on FSET selection and external synchronization.
PGOOD Output
The evaluation board has a PGOOD output that indicates the output voltage is in regulation. The datasheet provides details on the operation of the PGOOD output.
VCC Output
The evaluation board has a VCC test point which allows the user to monitor the output of the internal VCC regulators. No external loads should be applied to VCC.
Enable Jumper Configuration
The external circuitry around the Enable pin, EN, is tri-functional. If a
shunt is placed in the “ON” position (shorting the upper two pins of J1) then
EN is tied to VIN, forcing the converter to operate any time VIN is above
UVLO. The Under voltage Lockout section of the datasheet provides more details
on VIN UVLO. If a shunt is place in the “OFF” position (shorting the lower two
pins of J1), then EN is pulled to GND and the converter will remain disabled.
If no shunt is installed on J1, then EN is biased by a resistor divider from
VIN to GND, and the accurate enable function of the converter is employed. The
resistor divider sets the converter to turn on at a specific input voltage.
The standard evaluation board setup will result in converter turn-on when VIN
reaches approximately 7.2 V. The VIN turn-on voltage can be adjusted by
varying R3, R4, or both.
Table 3: ENABLE Jumper Configuration
| Jumper | EN State | Description |
|---|---|---|
| ON | HIGH | Converter is on when VIN ≥ VIN UVLO. |
| OFF | LOW | Converter remains disabled. |
| OPEN | PROPORTIONAL to VIN | Converter turns on once VIN reaches the set turn-on |
threshold.
EVALUATION BOARD PERFORMANCE DATA
The following section provides an overview of the performance data of both the AHVA81805 and A81805-1 versions of the Evaluation Board.
Thermal Performance
The following figures show the thermal performance of both the A81805 and A81805-1 versions of the Evaluation Board.
Figure 3: A81805 Version Evaluation Board Thermal Behavior. VIN = 13 V, VOUT = 3.3 V, IOUT = 2.5 A.
Figure 4: A81805-1 Version Evaluation Board Thermal Behavior. VIN = 13 V, VOUT = 5.0 V, IOUT = 2.5 A.
EMI Performance
The following figures show the EMI performance of the A81805-1 Version
Evaluation Board under nominal VIN conditions and maximum load. This does not
reflect the overall EMI signature of an entire system containing the A81805 or
A81805-1 but does show that the converter is capable of easily meeting even
the stringent automotive CISPR25 Class 5 EMC standards.
NOTE: Allegro is not an accredited EMC laboratory. The information
presented here is provided for reference only.
Figure 5: Conducted Emissions (150 kHz – 108 MHz)
Figure 6: Radiated Emissions (150 kHz – 30 MHz)
Figure 7: Radiated Emissions (30 MHz – 330 MHz)
A81805 EVALUATION BOARD SCHEMATIC
Figure 8: A81805 Evaluation Board Schematic
A81805 EVALUATION BOARD BILL OF MATERIALS
Table 4: A81805 Version Evaluation Board Bill of Materials
ELECTRICAL COMPONENTS
Designator| Quantity| Comment| Description|
Manufacturer| Manufacturer Part Number| Label on PCB
C1| 1| 470 pF| CAP, CER, 470 pF, 50 V, C0G, 0402| Kemet| C0603C471J5RACAUTO|
C1
C2| 1| 4.7 µF| CAP, CER, 4.7 µF, 50 V, X7R, 1206| TDK| CGA4J1X7R1H475K125AC|
C2
C3, C4| 0| DNP| | | | C3, C4
C5| 1| 47 µF| CAP, ALUM, 47 µF, 20%, 50 V, SMD| Nichicon| UBC1H470MNS1GS| C5
C6| 1| 0.1 µF| CAP, CER, 0.1 µF, 50 V, X7R, 0603| Murata| GCM155R71H104KE02J|
C6
C7, C8| 2| 10 µF| CAP, CER, 10 µF, 16 V, X7R, 1210| Kemet| C1210C106K4RACTU|
C7, C8
C9| 1| 4.7 µF| CAP, CER, 4.7 µF, 16 V, X7R, 0603| Murata| GCJ21BR71C475KA01L|
C9
C10| 1| 0.1 µF| CAP, CER, 0.1 µF, 50 V, X7R, 0402| Murata| GCM155R71H104KE02J|
C10
C11| 1| 4.7 µF| CAP, CER, 4.7 µF, 50 V, X7R, 1210| Murata Electronics|
GRM32ER71H475KA88K| C11
L1| 1| 2.2 µH| FIXED IND 2.2 µH, 5.6 A, 35.2 mΩ, SMD| Coil craft|
XAL4020-222ME| L1
L2| 1| 4.7 µH| FIXED IND 4.7 µH, 4.5 A, 60 mΩ, SMD| Vishay Dale|
IHLP2020CZER4R7M11| L2
R1| 0| DNP| RESISTOR, 1%, 0402| Panasonic| | R1
R2| 1| 0 Ω| RESISTOR, 0 Ω, 1/10 W, 1%, 0402| Panasonic| ERJ-2GE0R00X| R2
R3| 1| 464 kΩ| RESISTOR, 464 kΩ, 1/10 W, 1%, 0402| Panasonic| ERJ-2RKF4643X|
R3
R4, R5, R6| 3| 100 kΩ| RESISTOR, 100 kΩ, 1/10 W, 1%, 0402| Panasonic| ERJ-
2RKF1003X| R4, R5, R6
U1| 1| A81805| ALLEGRO IC, 40 V, 2.5 A, SYNCHRONOUS BUCK CONVERTER WITH 6 µA
QUIESCENT CURRENT| Allegro Micro Systems| A81805KESJSR| U1
OTHER COMPONENTS
Designator| Quantity| Comment| Description|
Manufacturer| Manufacturer Part Number| Label on PCB
CN1| 1| VFIL| BANANA JACK – NON-INSULATED, 0.218″ LENGTH| Keystone
Electronics| 575-4| VFIL
CN2, CN4| 2| GND| BANANA JACK – NON-INSULATED, 0.218″ LENGTH| Keystone
Electronics| 575-4| GND
CN3| 1| VOUT| BANANA JACK – NON-INSULATED, 0.218″ LENGTH| Keystone
Electronics| 575-4| VOUT
J1| 1| Header 1×3| CONN HEADER VERT 3 POS 2.54 MM| Wurth Electronics|
61300311121| ENABLE
MS1, MS2, MS3, MS4| ****
4
| Standoff Screw| PAN HEAD SCREW, M3 X 8 MM, NYLON| Wurth Electronic|
97790803111| N/A – mount in corner hole
PCB| 1| Circuit Board| A81805 Evaluation BOARD REV: 0 JAN 2022| | | N/A
STND1, STND2, STND3, STND4| 4| Standoff| HEX STANDOFF, M3, NYLON| Keystone
Electronics| 25512| N/A – mount in corner hole
GND BAR1, GND BAR2| 2| GND
Connections
| GND BAR : TINNED 18 AWG COPPER BUS WIRE| | | GND
EN, PGOOD, SYNC, VCC| 4| Test point| PC TEST POINT, MULTIPURPOSE, YELLOW|
Keystone Electronics| 5014| EN, PGOOD, SYNC, VCC
VFIL, VIN, VOUT| 3| Test point| PC TEST POINT, MULTIPURPOSE, RED| Keystone
Electronics| 5010| VFIL, VIN, VOUT
GND, GND| 2| Test point| PC TEST POINT, MULTIPURPOSE, BLACK| Keystone
Electronics| 5011| GND
A81805-1 EVALUATION BOARD SCHEMATIC
Figure 9: A81805-1 Evaluation Board Schematic
A81805-1 EVALUATION BOARD BILL OF MATERIALS
Table 5: A81805-1 Version Evaluation Board Bill of Materials
ELECTRICAL COMPONENTS
Designator| Quantity| Comment| Description|
Manufacturer| Manufacturer Part Number| Label on PCB
C1| 1| 470 pF| CAP, CER, 470 pF, 50 V, C0G, 0402| Kemet| C0603C471J5RACAUTO|
C1
C2, C3, C4| 3| 4.7 µF| CAP, CER, 4.7 µF, 50 V, X7R, 1206| TDK|
CGA4J1X7R1H475K125AC| C2
C5| 1| 47 µF| CAP, ALUM, 47 µF, 20%, 50 V, SMD| Nichicon| UBC1H470MNS1GS| C5
C6| 1| 0.1 µF| CAP, CER, 0.1 µF, 50 V, X7R, 0603| Murata| GCM155R71H104KE02J|
C6
C7| 1| 47 µF| CAP, CER, 47 µF, 16 V, X5R, 1210| Murata| GRM32ER61C476ME15L| C7
C8| 0| DNP| CAP, CER 1210| | | C8
C9| 1| 4.7 µF| CAP, CER, 4.7 µF, 16 V, X7R, 0603| Murata| GCJ21BR71C475KA01L|
C9
C10| 1| 0.1 µF| CAP, CER, 0.1 µF, 50 V, X7R, 0402| Murata| GCM155R71H104KE02J|
C10
C11| 1| 4.7 µF| CAP, CER, 4.7 µF, 50 V, X7R, 1210| Murata Electronics|
GRM32ER71H475KA88K| C11
L1| 1| 10 µH| FIXED IND, 10 µH, 4.9 A, 40.9 mΩ, SMD| Coilcraft| XAL5050-103ME|
L1
L2| 1| 4.7 µH| FIXED IND, 4.7 µH, 4.5 A, 60 mΩ, SMD| Vishay Dale|
IHLP2020CZER4R7M11| L2
R1| 1| 88.7 kΩ| RESISTOR, 88.7 kΩ, 1/10 W, 1%, 0402| Panasonic| ERJ-2RKF8872X|
R1
R2| 0| DNP| RESISTOR, 1%, 0402| Panasonic| | R2
R3| 1| 464 kΩ| RESISTOR, 464 kΩ, 1/10W, 1%, 0402| Panasonic| ERJ-2RKF4643X| R3
R4, R5, R6| 3| 100 kΩ| RESISTOR, 100 kΩ, 1/10W, 1%, 0402| Panasonic| ERJ-
2RKF1003X| R4, R5, R6
U1| 1| A81805-1| ALLEGRO IC, 40 V, 2.5 A, SYNCHRONOUS BUCK CONVERTER WITH 6uA
QUIESCENT CURRENT| Allegro Micro Systems| A81805KESJSR-1| U1
OTHER COMPONENTS
Designator| Quantity| Comment| Description|
Manufacturer| Manufacturer Part Number| Label on PCB
CN1| 1| VFIL| BANANA JACK – NON-INSULATED, 0.218″ LENGTH| Keystone
Electronics| 575-4| VFIL
CN2, CN4| 2| GND| BANANA JACK – NON-INSULATED, 0.218″ LENGTH| Keystone
Electronics| 575-4| GND
CN3| 1| VOUT| BANANA JACK – NON-INSULATED, 0.218″ LENGTH| Keystone
Electronics| 575-4| VOUT
J1| 1| Header 1×3| CONN HEADER VERT 3POS 2.54 MM| Wurth Electronic|
61300311121| ENABLE
MS1, MS2, MS3, MS4
| ****
4
| Standoff Screw| PAN HEAD SCREW, M3 X 8 MM, NYLON| Wurth Electronic|
97790803111| N/A – MOUNT IN CORNER HOLE
PCB| 1| Circuit Board| A81805 Evaluation BOARD REV: 0 JAN 2022| | | N/A
STND1, STND2, STND3, STND4| 4| Standoff| HEX STANDOFF, M3, NYLON| Keystone
Electronics| 25512| N/A – MOUNT IN CORNER HOLE
GND BAR1, GND BAR2| 2| GND
Connections
| GND BAR : TINNED 18 AWG COPPER BUS WIRE| | | GND
EN, PGOOD, SYNC, VCC| 4| Test point| PC TEST POINT, MULTIPURPOSE, YELLOW|
Keystone Electronics| 5014| EN, PGOOD, SYNC, VCC
VFIL, VIN, VOUT| 3| Test point| PC TEST POINT, MULTIPURPOSE, RED| Keystone
Electronics| 5010| VFIL, VIN, VOUT
GND, GND| 2| Test point| PC TEST POINT, MULTIPURPOSE, BLACK| Keystone
Electronics| 5011| GND
PCB LAYOUT
Figure 10: Top Layer
Figure 11: Inner Layer
Figure 12 : Inner Layer 1
Figure 13: Bottom Layer
RELATED LINKS
https://www.allegromicro.com/en/products/regulate/regulators/single-output- regulators/a81805
Revision History
| Number | Date | Description |
|---|---|---|
| – | December 9, 2022 | Initial release |
| 1 | February 22, 2024 | Update to new template |
Copyright 2024, Allegro Micro Systems.
Allegro Micro Systems reserves the right to make, from time to time, such
departures from the detail specifications as may be required to permit
improvements in the performance, reliability, or manufacturability of its
products. Before placing an order, the user is cautioned to verify that the
information being relied upon is current.
Allegro’s products are not to be used in any devices or systems, including but
not limited to life support devices or systems, in which a failure of
Allegro’s product can reasonably be expected to cause bodily harm.
The information included herein is believed to be accurate and reliable.
However, Allegro Micro Systems assumes no responsibility for its use; nor for
any infringement of patents or other rights of third parties which may result
from its use. Copies of this document are considered uncontrolled documents.
Allegro Micro Systems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
References
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