MPPT with SM72442 and SM72295

Hi Joel,

First Question: You can use the internal amplifier but you must ensure that the output current sense resistor is on the high side (OUT+ side rather than OUT-)  and that current flow through it at all time. The current sense amplifier cannot sense the output current if the voltage at the current sense resistor falls below 5V.

That also meanse the when the output voltage is below 5V, the output current sense amplifier will not return a consistent value.               

Second question: The value of the output current sensed by the SM72445 on AIOUT is available through I2C. Panel Mode can also be forced either through I2C (reg3, bit 3 and 4) or through the PM pin (pin 28)

Third Question: Yes, see answer to first question

Florent

Hi Florent,

Thanks for your answers.

What do you mean when you said "That current flow througt it at all time" ?

Joel

Hi Joel,

I mean to make sure that output current flows through the resistor when the H-bridge is running OR when the panel mode switch is activated if you use the dedicated panel mode switch configuration.

If you use the panel mode implemented using the H-bridge option then of course, that requirement does not exist.

Florent

Hi florent,

I began my schematic for my MPPT module and I wish to make the pcb quickly.

Can you look at my shematic ( file in pdf attached with this post) ?

I quickly analysed the SM3320-RF-EV technical documentation and I made some modifications:

The current sensing for IOUT is built around RS101 in HIGH SIDE configuration. You note that I use the Panel mode with Q1 and Q2 connected between VIN and VOUT of my board. The PM_OUT (pin 11 of SM72442) control the SM72482. I don’t use the external current sensing amplifier U10 of SM3320-RF-EV board (you have already answered this question)

The OUTPUT voltage is sensing by a resistor divider (R126 and R125) connected to pin 15 of SM72442.

I don’t use the comparator U11B of the SM3320-RF-EV board. I think that the SM72442 can control the PM_OUT by reading directly the VOUT voltage after internal AD conversion (internal register of SM72442) ?

My microcontroller (powered by 3,3V) generate MR (MASTER RESET) for SM72240 and I externally reset the SM72442 in case of problems. Good idea or not ?

For the power, my regulator output is 9V (not 10 V as indicated on the schematic). I think it’s right for SM72295 

There are no capacitor between BOUT (of SM72295) and GND and BIN and GND (cleared on SM3320-RF-EV schematic) ?

I wait for you remarks and advices for this schematic. I wish that my test board works quickly with my schematic. After your answers, I’ll make the pcb with PCAD2002.

Thanks.

Hi Florent,

Have you already read my last post about my proposal of schematic diagram for my MPPT module board ?

I wait for your help to know if I didn’t make errors for my board. My MPPT module built around the SM72442 IC and others SolarMagic IC must work quickly. I’ve already bought these new components.

I look forward to your reply.

Kind regards.

Joel

Hi Joel,

Question regarding the schottky diodes on the output: Why did you add the schottky diode D2? Are you worried of current backfeeding into the system? What are you planning on using as a load?

If you want the option of forcing the PM mode through the PM pin, you might want to a route this pin to a connector.

A0-A6 are analog input that are sensed and sampled by the SM72442. Make sure that the voltage is stable enough on this pins. You might want to add some capacitance on them near the SM72442.

What do you use for Q100-Q103? Recomended Gate charge (Qg) is 100nC typ or less.

Florent

Hi Florent,

The Schottky diode D2 is used in accordance with page 1 of the application note AN-2124 (literature number : SNOSB84B) – Power Circuit design for SolarMagic SM3320. I plan to make two MPPT modules which will be connected in parallel to increase the OUTPUT power for my load.My load is a charger.

After reading of the application note AN-2124, I need  blocking diode for each of my MPPT module. The Bypass Diode D1 is not useful in this case ? (My MPPT module isn't in series).

The Diode D2 is necessary but not D1 ! Are you agree with me ?

I am going to take your idea to force the Panel Mode by connecting the PM pin of SM72442 to my MCU (pin A0 of J100 connector is free).

For the four N-MOSFET Q100 – Q103, I’ve already bought IRF3205ZPBF (the same is used for the SM3320-EV-RF board). 100 nC at 10V, RDSON = 6.5 mOhm at 66 A, 10V. I thing that it’s your choice.

For A0, A2, A4 and A6 analog inputs of SM72442, I can increase the capacitance of C129, C130, C131, C132 up to 1 uF. The voltages must be well filtered with these capacitance. The U105 output ( 5V regulator) must also be stable with C155 (10 uF, Tantalum).

You don't answer to a question in the last post : I'm going to remove C142 and C143 (AIIN and AIOUT pins) as made on the SM33206RF6EV board. Good or Bad idea ?

After these modifications, all seems to be right on the schematic ? Can I begin my PCB.

Thanks a lot for your support. I look forward to your reply.

Kind regards.

Joel

Hi Florent,

Did you studied my answers and my news questions posted last Friday (about the MPPT module) ?

I've already joined the schematic diagram suggested. is it ok  ?

I look forward to your reply.

Kind regards

joel

Hi Joel,

Sorry, I missed part of the A0 to A6 connection and I thought you connected them directly to your MCU. That's OK, you won't need more capacitance there, no need to switch to tantalum.

I agree, you should not need D1

I suggest you keep the pads for the capacitors but do not stuff the components and see if you have noise issues. You might also want to to put 0ohms resistors between BIN and AIIN and BOUT and AIOUT. This gives you the option to add filtering shall you need it. In later revisions, you can get rid of both resistors pads and capacitor pads if you find you don't need them.

Best Regards,

Florent

Hi Florent,

I realized my pcb for my MPPT Module with SM72442 and SM72295. For the moment, I used through hole components (SM72442 on a TSSOP28 – DIP28 adapter and SM72295 on a SOIC28 – DIP28 adapter). The input will be connect to a 50 Wp PV panel.

I want to read and write the SM72442 internal registers. My master microcontroller initiate the I2C communication with my SM72442 device address : $02 with I2C0 = 1, I2C1 = 0 and I2C2 = 0.

After sending this address (Frame 1), the acknowledge is OK (ACK =0). Now, I want to read or write data to monitor the MPPT with SM72442.

I need information about Frame 2 (command register byte). What is the value for this register ?

Could you help me ?

0xE0 to read Reg0, 0xE1 to read Reg1, 0xE2 to write or read Reg2, 0xE3 to write or read Reg3, 0xE4 to write or read Reg4, 0xE5 to write or read Reg5 ?

I’m not sure for these values.

For information, my SM72442 is always in PANEL MODE (sqaure wave on PM OUT).

I look forward to your reply.

Kind regards.

Joel

Hi Florent,

I need help for I2C communication between MCU and the SM72442. I tried the I2C read sequence and I have troubles.

After sending the device address with W\ = 0, then ACK = 0 !

After sending the Frame 2 (Value = 0xE0), ACK = 0.

After sending device address with R = 1, then ACK = 0 !

After reading the Frame 4 (0x07), ACK =1 ????

And All Data Bytes are $FF (for example, Voltage on A2 isn’t equal 5V).

Can you help to read and write correctly in SM72442 ?

I look forward to your reply (for the two last post)

Kinds regards

Joel

Hi Joel,

When you say ACK=0 Do you mean SDA=0 which indicates acknowledge?

First initiate a transaction with a write to the address.

Then pass the register to the SM72442 0xE0 for address 0, 0xE1 for address 1 etc...

Then perform a restart and address the SM72442, this time with a read command

Next comes the register 0x00 for address 0, 0x01 for address 1 etc...

The SM72442 should acknowledge each of these bytes up to that point.

The SM72442 should then send back the number of bytes in the register (should be 7) and the content of the registers byte by byte starting with the lower bytes.

The MCU should acknowledge each of these bytes.

If you read 0xFF I think the SM72442 is not returning any data and the SDA line is just hanging high.

Regards,

Florent 

Hi Joel,

In my previous reply i mentioned you need to set register 0x00 for address 0, 0x01 for addres 1 etc...

Scratch this line, just send the I2C addres with the read command attached to the byte and the SM72442 will already be configured for you to read from the register you selected with the 0xEn register command earlier.

Sorry for the confusion,

Florent

Hi Florent,

I read your last posts and I made the same thing (SCL and SDA timing attached with this post).

After sending the reading Address, the SM72442 returns 0x07 (number of register) and ACK=1 (SDA =1) No Acknowledge.

The SM72445 send back several $FF byte with ACK=0 (ACKNOWLEDGE).

Something is wrong !!!!!

I don’t understand and my project is stopped.

An idea to help me ???

Kinds regards

Joel

Hi Joel,

If the SM72442 is returning 0x07 after issuing a read command, the MCU should acknowledge reception of the bit, not the SM72442

If the SM72442 is acknowledging after every byte, it is probably in write mode and is listening to the MCU..

After you issue a write command with 0xE0 as the register (for example), you need to issue a re-start to restart a new transaction with the SM72442. Once the SM72442 is in read mode, it wil acknowledge and send 0x07. The master (MCU) will have to acknowledge this bit and all the further bits until you stop the transaction. 

It's a little hard to tell on the waveform capture who is acknowledging. but try to acknowledge after the SM72442 sends the byte containing 0x07 and see if this works

Best Regards,

Florent