TPS25946: Part details clarification

Hi Carlo,

Thanks for reaching out to us. We are currently on Holidays.

Please expect delay in response.

Hi Carlo,

Here is my response:

1. As such no layout recommendation. You can keep far.

2. Cout is decided as per application and not needed for device to work. Small Cout like 0.1uF helps in decoupling.

3. D3 and D4 are optional and would be a different parallel path other than resistor-diode series connection. 

4. yes

5. yes

6. No plan for automotive variant of this device. Currently only this efuse which provides bidirectional control. 

7. Yes

8. We tested TPS2595 in that configuration as mentioned in app note and results were good, other devices have not been tested in that configuration. But later we found some issue in using TPS2595 in bidirectional configuration so we are not recommending to use device in bidirectional configuration that is not designed for bidirectional use . 

9. Are you using any battery charging IC? I think it should be used. Then we can follow fig 9-3. 

Regards

Kunal Goel

Hello Kunal,

Regarding questions 8 and 9, please see below.

8. Are there any IC that I can use as a switch and has bidirectional capability in an automotive setting?

9. See additional figure #1. Yes, I am using a battery charging IC to connect solar arrays to battery, but unfortunately it is not from TI (it is called LT3652). The pink star signifies the location of the battery charging IC.

10. See additional figure #2. As far as I know, TPS25946 is the only IC that can act as a switch and has bidirectional capability so this is what I used with conjunction with U2 (BQ29209) in my circuit. Having said that and given the schematics, is it more preferrable to connect pin IN to the battery module? I don't think I can follow the schematics in Fig. 9-3 since my battery charger is somewhere else and the USB-C is only used before rocket launch. Please correct me if I'm wrong. I still posit that pin IN is connected to battery module.

Regards,
Carlo

Hi Carlo,

1. How much should be voltage rating and current limit of switch?

2. I think IN pin connected to battery is fine because current limit is from IN to OUT. For overcurrent protection when power flows from solar array to battery I think the battery charger will take LT3562 will take care. One thing when power flows from OUT to IN , are we ensuring TPS25946 device EN pin is getting voltage above 1.2V to enable device?

Regards

Kunal Goel

Hello Kunal,

Please see below:

1. Voltage rating should be >8.4V. This is the maximum voltage of the battery module. The current limit is about 2A.

2. I have read the datasheet of TPS25946 and the inclusion of the series resistor - diode should be able to provide the required "minimum voltage (VUVP(R)) available at the IN pin". This quote is from the datasheet. I also followed the equation found in Sec. 9.2.2.7 for the resistor and diode requirements. Should I also compute the voltage for EN pin? Section 9.2, for OTG mode, didn't mention about pin EN. They only mentioned about VUVP(R) for the OUT to IN power path to work. Please clarify on this matter.
Regards,
Carlo

Hi Carlo,

1.  Let me check with team on automotive device. Will customer only use automotive qualified device or that is not a very strict requirement?

2. In the application shown in datasheet EN pin is connected to MCU, so MCU will take care of making EN high.  But in this application it is not like this I think. EN is connected to a resistor divider, so we have to ensure that VIN is that much it makes EN above 1.2. From calculation VIN should reach around 2.8V because of diode , resistor network. 

Regards

Kunal Goel

Hi Kunal,

Regarding your response below, our customer has this concern.

Kunal Goel said:

8. We tested TPS2595 in that configuration as mentioned in app note and results were good, other devices have not been tested in that configuration. But later we found some issue in using TPS2595 in bidirectional configuration so we are not recommending to use device in bidirectional configuration that is not designed for bidirectional use . 

While I was looking for more bidirectional switches, I encountered this forum post about using a hot swap controller for bidirectional current. It was already reviewed by an E2E expert but this was 2 yrs ago. Moreover, you mentioned that your team encountered a problem with TPS2595 in bidirectional configuration in the later test AFTER publishing the application report. So now, I am asking you again if the configuration in this forum post is doable (in this context of the TPS2595 issue) for bidirectional current. You can see the link here:

e2e.ti.com/.../lm5069-bidirectional-switch-for-capacitive-load---schematic-review
Regards,
Carlo

Hi Carlo,

I will not recommend TPS2595 for bidirectional control. I will recommend TPS25946 instead. 

Regards

Kunal Goel

Hello Kunal,

Thank you for the recommendation. Please see below response to the previous questions.

Kunal Goel said:

1.  Let me check with team on automotive device. Will customer only use automotive qualified device or that is not a very strict requirement?

1. I need to use minimum of automotive rating. This is highly preferred.

Kunal Goel said:

2. In the application shown in datasheet EN pin is connected to MCU, so MCU will take care of making EN high.  But in this application it is not like this I think. EN is connected to a resistor divider, so we have to ensure that VIN is that much it makes EN above 1.2. From calculation VIN should reach around 2.8V because of diode , resistor network. 

2. For reference using Sec. 9.2.2.7 equation, I am using VOUT = 8.4V, VF = 0.4V, ILOAD = 0.1A. This provides R5max =54.7. I chose 11ohms. VOUT = 8.4V since the battery module is in 2S2P configuration (U3, U4, U5, U9). Using V=IR, I found that pin EN will see 2.9V. Can you please verify this from your part so I can be on the same page as you?
Regards
Carlo

Hi Carlo,

Regarding 2nd point , equation looks fine to me and EN pin will also be above 1.2V . Just one thing customer is sure that their initial load current is 0.1A?

Regards

Kunal Goel

Hello Kunal,

Please see below response.

1. I am not sure of the 0.1A initial loading since I only copied this value from the datasheet. Could you please help me in figuring out a reasonable value?

2. Is the design in this E2E post (e2e.ti.com/.../lm5069-bidirectional-switch-for-capacitive-load---schematic-review) still operational given TI's current technology? Will this back-to-back configuration run smoothly (unlike the back-to-back configuration of TPS2595 in the application report)?

Regards,
Carlo

Hi Carlo,

1. 0.1A in datasheet is assumed based on USB type-C load like headphones. I am not aware how much current spacecraft load will draw. May be based on testing later we can tune series resistor and diode value. 

2. If they are very much interested in automotive grade part then they can also have a look at solution in this post using LM5060-Q1 in B2B. Please take relevant details from this post before sharing with customer as it is internal forum thread so may contain confidential info.

https://e2e.ti.com/support/power-management-group/power-management---internal/f/power-management---internal-forum/1066683/power-switch

3. Also can you help check from customer why they are interested in automotive grade part ? This will help us in our portfolio development. 

Regards

Kunal Goel

Hello Kunal,

Please see below response:

1. Am I to take that "initial load" in the datasheet Sec. 9.2.2.7 means its the maximum current of the load (regardless if it is coined "initial")?

3. I am interested with automotive part since "Q100 devices qualified for high-reliability automotive applications targeting zero defects."
Regards,
Carlo

Hi Carlo,

1. No not the max current. But when the supply is applied to load then during initial turning on of the load how much current load draws. They have to first observe their load current profile during turn on phase or as I said they can adjust later series resistor and diode value. 

Let me know if I can close the thread or if any further query. 

Regards

Kunal Goel

Hello Kunal,

Since the TPS25946 has no automotive part, while the LM5060-Q1 B2B configuration may work, it requires too many external components that occupy board space.

The customer is using 2 units of TPS25940 in this configuration to mimic a bidirectional switch. It is an automotive rating, the nonworking efuse has reverse current protection, not much externa components like the hot swap controller, has shutdown control using an NMOSFET.

May you please review the design and check if this will work theoretically and electrically?

Thank you.

Regards,
Carlo

Hi Carlo,

I will get back at earliest on this.

Regards

Kunal Goel

Hi Carlo,

Looks fine. I was thinking the CDH should go to one device and CDH compliment to another device. Because when one path is active the other should be disabled. I believe they are using CDH signal for that purpose only ? but same CDH goes into both path.

Regards

Kunal Goel

Hello Kunal,

Please see below response.

1. Actually, the CDH port is connected to the pin OUT of BQ29209-Q1. By doing this, I am isolating the battery module (denoted by BATT+) from the rest of the circuitry. Both power path will both be activated once BQ29209-Q1 makes pin OUT low again.

2. Furthermore, is the implementation of the transient protection components ok? Are they not redundant? Due to this B2B configuration, there is a TVS along pin OUT and a schottky diode in pin IN. Won't they perform erratically?

Regards,
Carlo