Texas Instruments | AN-2122 SM3320-RF-EV Reference Design (Rev. E) | Application notes | Texas Instruments AN-2122 SM3320-RF-EV Reference Design (Rev. E) Application notes

Texas Instruments AN-2122 SM3320-RF-EV Reference Design (Rev. E) Application notes
Application Report
SNOSB82E – November 2010 – Revised May 2013
AN-2122 SM3320-RF-EV Reference Design
.....................................................................................................................................................
ABSTRACT
The SolarMagic™ SM3320-RF-EV reference design integrates a power optimizer and a low-cost 2.4GHz
radio to add a remote shutdown feature to a PV system. The remote shutdown feature can be used during
installation, maintenance, or emergency situations to de-energize the PV system.
1
2
3
4
5
Contents
Introduction .................................................................................................................. 2
System Overview ........................................................................................................... 2
SM3320-RF-EV Design Specification .................................................................................... 3
3.1
SM3320 RF-EV Kit ................................................................................................. 3
3.2
Features ............................................................................................................. 4
3.3
Design Description ................................................................................................. 4
3.4
Flash Programming ................................................................................................ 6
3.5
I2C Interface ........................................................................................................ 7
3.6
Layout Consideration .............................................................................................. 8
3.7
Heatsinking ......................................................................................................... 8
3.8
Test Setup .......................................................................................................... 8
Schematic .................................................................................................................. 10
References ................................................................................................................. 11
List of Figures
1
System Overview Showing Intended Application of SM3320-RF-EV Board in a PV System ..................... 3
2
Forced Panel-Mode and Reset Using nRF24LE1 ...................................................................... 4
3
Power Line Antenna Implementation ..................................................................................... 5
4
Inductor Dimension ......................................................................................................... 5
5
Connector Board interface ................................................................................................. 7
6
Test Setup for SM3320-RF-EV............................................................................................ 8
7
RF Shutdown ................................................................................................................ 9
1
SM3320-RF-EV Design Specification .................................................................................... 3
2
Pinouts for 10 Pin Headers and Nordic Motherboard .................................................................. 6
List of Tables
SolarMagic is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
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1
Introduction
1
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Introduction
Although its principal purpose is to communicate shutdown intent, this RF system is 2-way and can be
used for a wide variety of communication applications, including monitoring, security and identification.
The SolarMagic SM3320-RF-EV is based off of the SM3320-1A1 power optimizer, and shares all of its
best-in-class power optimization features. This includes its ability to mitigate real-world mismatch, its
99.5% peak efficiency, and its Panel-Mode operation. In addition, the same ultra-low profile form factor of
the original SM3320-1A1 is maintained so that it can be integrated into the same junction box designs.
This evaluation board should work as a power optimizer even without a transmitter
The wireless RF communications in the SM3320-RF-EV is implemented using a low-cost Nordic
nRF24LE1 chip. This is a low-cost, 2.4GHz radio and 8051 microcontroller on a single chip. The 2.4GHz
radio uses narrow band modulation (as opposed to direct sequence spread spectrum), which can be used
either with or without frequency hopping. Example software is provided that implements the remote
shutdown feature on the 8051 microcontroller in the nRF24LE1.
One of the unique features of the SM3320-RF-EV is its use of the DC power lines as an RF antenna and
transmission line. This enables the SM3320-RF-EV to maintain radio communication even when it is
mounted in the junction box of the module. This antenna design can be used with other 2.4GHz radio
chipsets besides the nRF24LE1 by straightforward modification of the provided design files.
The SM3320-RF-EV reference design provides a flexible platform for developing value added features in
firmware with no additional hardware development. Examples of these features include module-level
monitoring, security (theft-detection and theft-deterrence), and identification. Similarly, firmware
development on this platform can be used to customize the SM3320-RF-EV to be compatible with an
existing monitoring system or inverter communication protocol if a customer desires.
SolarMagic technology is an overall solution that works in existing and new installations, residential,
commercial, and utility scale projects. Texas Instruments 50 years of experience in the electronics industry
delivers unsurpassed manufacturing, design, and development technology.
2
System Overview
Figure 1 depicts how the SM3320-RF-EV design would be implemented in its intended application. In this
example, every module is connected to an SM3320-RF-EV power optimizer. Under normal conditions, the
central transmitter sends a signal to each SM3320-RF-EV power optimizer indicating that it is ok to
operate and output power. When an emergency condition occurs, the central transmitter will send a signal
command to all the SM3320-RF-EV to shutdown. This de-energizes the output of each SM3320-RF-EV,
and in doing so brings down the voltage of the DC bus and all DC wiring to a safe voltage level.
2
AN-2122 SM3320-RF-EV Reference Design
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DC Disconnect
Combiner
Central
transmitter
Nordic
nRF6310
Receiver
SM3320-RF-EV
Remote shutdown switch
Figure 1. System Overview Showing Intended Application of SM3320-RF-EV Board in a PV System
3
SM3320-RF-EV Design Specification
Table 1. SM3320-RF-EV Design Specification
Symbol
PV Module MPP Voltage
PMPP
PV Module Power
VOC
PV Module Open Circuit Voltage
ISC
PV Module Short-Circuit Current
VOUT
Output Voltage
Min
Typ
15 Vdc
10 W
350 W
50 Vdc
11A
0 Vdc
43 Vdc
IOUT
Output Current
Overvoltage Protection Threshold
OTP
Overtemperature Protection Threshold
125oC
MPP Efficiency
98.5%
Panel-Mode Efficiency
99.5%
PMEFF
Max
40Vdc
OVP
MPPEFF
3.1
Parameter
VMPP
12.5A
45V
SM3320 RF-EV Kit
Included in the SM3320-RF-EV are the following items:
• SM3320-RF-EV PCB
• Software for the Receiver (SM3320-RF-EV) – compiled and source code
• Software for the Central Transmitter (nRF6310) - compiled and source code
• Design files – Schematic, BOM and Gerbers
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SM3320-RF-EV Design Specification
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In order to get started as quickly as possible with this kit, users are recommended to purchase a Nordic
nRF6310 motherboard. Using the included Central Transmitter sample code will enable users to test the
enable/disable and Panel-Mode functionality.
3.2
Features
•
•
•
•
•
•
3.3
Wireless shutdown for SM3320-1A1
Wireless Panel-Mode operation for SM3320-1A1
MPPT for Photovoltaic Panel
2.4 GHz ISM band operation
Enhanced 8 bit 8051 compatible microcontroller
Power line antenna
Design Description
The Sirius RF evaluation board shares the same power specifications as the SolarMagic SM3320-1A1
Power Optimizer. The controller for the power optimizer consists of an SM72442 programmable MPPT
controller for PV panels and a Nordic nRF24LE1 low power system-on-chip wireless solution. The
nRF24LE1 has a built in 2.4GHz transceiver (250kbps, 1Mbps and 2Mbps air data rates) and an 8051
compatible microcontroller. Operation at 250kbps is recommended.
3.3.1
Receiver
The nRF24LE1 IC will be located in the SM3320-RF-EV board and used as a receiver that controls the
forced shutdown and Panel-Mode operation.
By utilizing these two ICs (SM72442 and nRF24LE1),the evaluation board is capable of tracking the
maximum power point of PV panels during normal operation as well as controlling a shutdown during
emergency conditions. Two of the GPIO outputs (P0.0 and P0.1) from the microcontroller are used to
send a shutdown or Panel-Mode signal into the SM72442. The shutdown signal will pull the RESET pin
low in order to deactivate the PWM signals that are coming out from SM72442. Panel-Mode operation can
be forced on the SM72442 by pulling the PM pin of the SM72442 low.
5V
60.4k
RST
P0.0
2N7002
10k
5V
nRF24LE1
F16Q32
SM72442
60.4k
PM
P0.1
2N7002
10k
Figure 2. Forced Panel-Mode and Reset Using nRF24LE1
4
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Figure 2 shows one sample application where the GPIO outputs of nRF24LE1 are used to force a reset or
Panel-Mode condition on the SM72442. The nRF24LE1 radio uses the power line as an antenna by
coupling into the output wire of the SM3320-RF-EV. This implementation is shown on Figure 3. In order to
not short the output of the radio to ground, an air wound inductor (L104 in schematic) is placed between
the OUT (-) terminal and the actual string wire. The inductor, together with the capacitors to ground at the
DC power feed (C116) and the series capacitor between it and the RF transceiver device (C113), create
an LC Network to couple RF in and out of the string wire terminal without shorting it to the DC power feed,
and at the same time carrying the DC from the power feed to the string wire. The other string wire has a
capacitor (C117) to ground to provide a return for the RF through the ground planes to the RF transceiver
device. The dimensions for the air wound inductor are attached in Figure 4. This inductor introduces
approximately 10 dB loss at 2.4 GHz. For better manufacturability, the inductor can be redesigned with a
core so it is smaller. It still needs to carry the full string current
String Wire
SM3320-1A1
C117
OUT (-)
nRF24LE1
F16Q32
Balun
Network
Terminal (+)
L104
Terminal (-)
C113
C116
String Wire
Figure 3. Power Line Antenna Implementation
Specifications:
1) Number of Turns: 2
2) Wire AWG: 17
3) A:0.260 inch
4) B:0.820 inch
5) C:0.300 inch (center to center of the wire)
6) D:0.560 inch
7) E:0.400 inch
A
B
Bending Axis
D
E
C
Mounting Points
Should not be
insulatedup to
bending axis
Figure 4. Inductor Dimension
3.3.2
Central Transmitter
For this evaluation board, a Nordic module (nRF2723) is used as a transmitter. In general, any Nordic RF
module with an nRF24xx IC and external antenna connection can be used as a transmitter, however
additional software development could be required. To minimize programming and hardware development
time, the transmitter can be made of a Nordic RF module with nRF24xxIC along with Nordic Motherboard
(nRF6310), which is included in the Nordic starter kit nRF6700. You can download the transmitter.hex file
included in this kit onto the Nordic module in order to use it as a transmitter to send a shutdown or PanelMode signal towards the receiver. The motherboard has buttons that can be manually connected to the
GPIO pins from the module. By doing this, the transmitter module will receive button input from you and
send an appropriate signal towards the receiver located on the SM3320-RF-EV board.
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Both sample codes and hex files for the receiver and transmitter are provided in the .zip file.
3.4
Flash Programming
A Nordic Motherboard (nRF6310) is required to program the transmitter and receiver ICs. The sample
code and hex files provided can be used as a start to program both ICs. Please remove R101 and R102
from the board before downloading the .hex file into the receiver. The receiver IC in the SM3320-RF-EV
board is pre-programmed with functions to enter a reset condition or to operate into a forced Panel-Mode
condition. Logic high will appear on P0.0 and P0.1 of the receiver IC once an appropriate signal command
is received from the transmitter. You also have the flexibility to program the Flash memory in the receiver
IC by using the 10 pin connector (J101 on schematic) located in the board. These 10 pins should be
connected with the external ISP interface on the Nordic Motherboard (nRF6310) to enable the in-circuit
programming. Table 2 shows the table of pinouts for the 10 pin header on SM3320–Rf-EV board and an
external ISP interface from the Nordic Motherboard.
Table 2. Pinouts for 10 Pin Headers and Nordic Motherboard
Pin
10 Pin Headers
1
P0.4
Nordic Motherboard (nRF6310)
RF_VDD
2
PROG
Not Used
3
SCK
PROG
4
GND
CSN
5
MOSI
MOSI
6
GND
RESET
7
MISO
MISO
8
3.3VDC
SCK
9
CSN
Not Used
10
RESET
GND
Each of the pins of the 10 pin header should be connected to the appropriate pin on the Nordic
Motherboard. Pin 1 of the 10 Pin Header can either be connected to pin 2 of the Nordic Motherboard or it
can be left floating during programming. All of the other pins on the header should be connected to its
appropriate pin on the Nordic nRF6310 external interface. For example pin 2 on the header should be
connected to pin 3 of the Nordic nRF6310. The SM3320-RF-EV kit also provides a schematic and gerber
file for a connector board, which will aid in the programming between the receiver IC and the Nordic
nRF6310 motherboard, as shown in Figure 5. You can then download your own hex file into the Flash
memory of nRF24LE1 that is located on the SM3320-RF-EV board.
The RF_VDD (pin 1 of nRF6310) should be connected to the 3.3VDC (pin 8 on SM3320–RF-EV). Since
the RF_VDD pin is used as a signal level shifter on the Nordic Motherboard, the power supply voltage
from the motherboard does not need to match the power supply voltage from the application board
(SM3320-RF-EV in this case). However, an input voltage of minimum 15V should be applied to the
SM3320-RF-EV in order to provide a 3.3VDC voltage on pin 8 of the header.
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Figure 5. Connector Board interface
In order to start programming on the nRF radio IC, the following software has to be downloaded:
1. µVision IDE from Keil
2. nRFgo Studio
The nRFgo Studio is provided on the nRFgo Starter Kit (nRF 6700). The nRFgo Studio will download the
.hex file generated by µVision IDE into the flash memory on the receiver. To program the flash using the
external ISP interface from the motherboard, an nRF ISP interface has to be manually selected in the
nRFgo Studio. A complete download of the hex file into the IC is indicated by a successful verification of
the flash memory. Note that both R101 and R102 (see Section 4) on the SM3320-RF-EV board have to be
removed during the programming.
3.5
I2C Interface
Using a connector board that is supplied in this kit, you have the ability to access the SCL and SDA pins
on the SM72442 as well as W2SCL (P0.4) and W2SDA (P0.5) on the 32 pin nRF24LE1. Pin 1 and 3 on
the 10 Pin Header are connected to P0.4 and P0.5 respectively through R101 and R102, see Section 4.
Please make sure that both resistors are assembled on the SM3320-RF-EV board. The SM72442 and
nRF24LE1 are cond as a slave. A master can be used to communicate to SM72442. External pull-up
resistor of 2kΩ to 3.3V is required. The address for SM72442 is 1 whereas the address for the nRF24LE1
can be cond using setting the address W2SADR on the SFR register (for more information, see the
nRF24LE1 data sheet from Nordic Semiconductor). The I2C protocol for communicating with SM72442
can be found on the SM72442 Programmable Maximum Power Point Tracking Controller for Photovoltaic
Solar Panels Data Sheet (SNVS689).
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SM3320-RF-EV Design Specification
3.6
Layout Consideration
•
•
•
3.7
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RF IC layout assumes an adjacent ground plane. If the adjacent layer is a power plane, a bypass
capacitor should be added between ground and power plane in the vicinity of the RF IC. In our case,
three 0.01µF and three 100pF capacitors are connected between ground and the power plane, and are
placed near nRF24LE1.
The distance from an RF trace and a plane around it should be at least two times the width of the RF
trace to avoid co-planar coupling that lowers the line impedance, unless co-planar ground flood is
included in the calculation.
The trace going into the crystal oscillator should be wide enough (~15 mils in our case) to reduce the
line inductance for more reliable starting at low temperature. On the other hand, increasing these
traces should also increase the line capacitance to ground, which can affect starting as well. However,
this effect can be counteracted by reducing the value of C105 and C106.
Heatsinking
SM3320-RF-EV evaluation board does not come with a heatsink. Therefore, in order to run the evaluation
board at elevated power ratings, an appropriate heatsink should be added on Q1, Q2, Q3 and Q4 as well
as diode D1. Care must be taken prevent electrical contact between the drains of the MOSFETs in the
process of proper heatsinking. At elevated power operation please note the increase in temperature
across these semiconductor devices.
3.8
Test Setup
To perform an evaluation on a single SM3320-RF-EV, it is suggested that you connect the input to a solar
array simulator (SAS) and the output to a load bank.
SAS
Voc = 35 ; Vmp = 30
Isc = 2.5A; Imp = 2A
SM3320
RF-EV
ELECTRONIC
LOAD
Figure 6. Test Setup for SM3320-RF-EV
Listed below are example settings for the SAS and electronic load:
3.8.1
SAS
Voc = 35V; Vmp = 30V; Isc = 2.5A; Imp = 2A.
Electronic Load: Constant Current Mode (CC) at 1.5A
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3.8.2
Test Results
Figure 7. RF Shutdown
When the electronic load is turned on at 1.5A load current, SM3320-RF-EV will operate in Panel Mode for
at least 128 seconds. After this period, the MPPT mode is then entered. During MPPT, the output voltage
is at 38V with an input voltage of 30V. Once the shutdown signal is received by the receiver, one of the
Nordic GPIO output will pull the reset line down causing the SM3320-RF-EV to stop switching and
resulting the output voltage will go down (Figure 7).
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Schematic
4
10
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Schematic
AN-2122 SM3320-RF-EV Reference Design
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References
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5
References
•
•
SM72442 can be found on the SM72442 Programmable Maximum Power Point Tracking Controller for
Photovoltaic Solar Panels Data Sheet (SNVS689)
nRF24LE1 data sheet from Nordic Semiconductor
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