MP2722 V_SYS_MIN behaviour

Battery Management
1

Hi,

I’m using MP2722 in my device prototype. My understanding of documentation was that output voltage on V_SYS is always higher that V_SYS_MIN. However regarding my tests when Vin is disconnected V_SYS is almost V_BATT. Is it expected or did I do some incorrect testing?

Problem is that my device requires at least 3.7V to work correctly. If I can;t set this thru V_SYS_MIN I have to add some booster (which I would like to avoid). Are you offering any other deice, which can provide min 3.7V (min 2.5A) on output with one cell and USB-C supported?

2

Hi Dawid,

Thanks for reaching out. I understand you’re facing an issue when you disconnect Vin you see the system voltage track the battery voltage. You are correct in your assumption that the output voltage should be greater than V_sys_min.

This is expected. When Vin is absent, the Battery FET (BATTFET) turns fully on to pass the battery power to the system, according to the datasheet (pg. 19).

To get a better understanding, what you are trying to test by disconnecting Vin? What is your test setup?

For now, I can recommend the MP2731. This part has a slightly higher V_sys_min, can provide your desired output power, and has DRP detection capability. Additional resources including an MPS reference design, schematic, and layout file can be found here:

MP2731 USB PD Reference Design: 4.5A, NVDC Single-Cell Charger with OTG | Reference Design | MPS (monolithicpower.com)

Hope this helps!

3

Thank you for answer.

Now I’m little confused: you have written that

You are correct in your assumption that the output voltage should be greater than V_sys_min.

and

When Vin is absent, the Battery FET (BATTFET) turns fully on to pass the battery power to the system, according to the datasheet (pg. 19).

(To just clarify ) let’s assume that we have disconnected USBc (V_IN disconnected) and battery level is around 3.2V. What will be the V_SYS voltage (approximately)? Is it going to be around 3.2V right?

I guess MP2731 is working in similar way. if V_IN is disconnected, V_SYS will be around V_BAT, and it might be lover than V_SYS_MIN Is it correct understanding?

My setup is mp2722 with recommended in datasheet application. USB-C connector connected to charger 5V/3A. Battery LIPO.
First I’m charging battery (V_IN connected) than I’m disconnected USB-C and measure V_SYS.

4

I have forgotten to mention that my LOAD is connected to V_SYS

5

Hi Dawid,

Thanks for providing additional context.

Apologies for the confusion, let me clarify:

V_SYS_MIN is the minimum system voltage setting. This setting is used to compare to VBATT such the IC will regulate the system voltage to the desired level when the input is connected. See below for NVDC operation for the MP2722.

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When Vin is disconnected, charging is disabled and V_SYS will be approximately V_BATT + V_TRACK (150 mV). So, in this case it will be 3.35 V, and it can be lower than V_SYS_MIN. The MP2722 defaults to V_SYS_MIN = 3.588 V.

To ensure the system is always regulated to at least 3.7 V when the input is connected, set the V_SYS_MIN register (06h) to 110: 3.763V.

Hope this provides you with some clarification.

6

Now everything is clear. Thanks for that.
It means that I need additional booster after charger block to increase voltage to level of my needs (when V_IN disconnected). Are you offering other charger device, which already has output booster, which regulates output to specific value (I need 3.7V and at least 2.5A)? I would still need usb-C support and power path sharing (feeding load with battery, V_in or both)

7

Hi Dawid,

I would recommend the MP2770.

This part has USB-C capabilities and can deliver power to the system from Vin passthrough and the battery. Additionally, in the absence of an input source, the device works in boost mode with an output current of up to 3.65A.

1 Like
8

Hi, one more question regarding mp2722. Can I use PMID to supply my system instead V_SYS?
When V_IN is disconnected I could use i2c to turn on boost and as I understand on PMID I may have 5V right?

Regarding mp2770. My understanding of documentation is that this IC is not supporting power path sharing so it is not possible to charge battery and supply my load e.g. on SYS pin. Is it correct understanding?

9

Yes, you can connect your system to PMID. There are a few things to note here:

  1. If Vin is unplugged, PMID voltage will drop, PMID voltage may drop to 0V before boost is enabled by host. So if you need consistent power on system, it can’t be connected to PMID.

  2. Once boost is operating, QR is turned on, VIN will have the same voltage as PMID. Boost output current is not limited since QR is bypassed.

The MP2770 can charge the battery and provide power to the system when input power is present. See snippet from datasheet pg 23 below.
image

10

Thank you. Everything is clear now.