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TPS2115A: Configuration for manual or automatic switching & consumption current values

Adrian Cobos
Prodigy 90 points
Part Number: TPS2115A
Other Parts Discussed in Thread: TPS2121

Hello, I'm going to give some context first so you might understand our situation more easily

We want to design 2 different power management system with some diverse features as following:

Type A Expected features

  • Automatic Switching - system must change to back-up battery automatically when main supply fails. There is no decision level, so main supply is 5v when active, or none if fails. Power supply must return to major priority power supply if it returns.
  • Switchover time - As less as possible to prevent MCU reset, so seamless system is mandatory.
  • Output voltage - As less as possible to prevent MCU reset. Voltage must not fall below 3v any case.
  • Current Consumption – Systems works in two different stages, low current sleep mode and high-performance mode; because of that, we need good efficiency and very low Iq operating power management to not increase total sleep consumption from both power supply sources and achieve a maximum of 200 mA.

Type B. Expected features

  • Automatic or manual Switching - Both options are valid
  • Switchover time – A seamless system might be perfect, but breaks could be acceptable instead Instrumentation is able shutdown and restart with new power supply.
  • Output voltage - As less as possible to prevent instrumentation bad function. Voltage must not fall over 4.8Vdc any case.
  • Current Consumption – Power managements must achieve a maximum of 2A continuous consumptions.

With the aim of avoiding problems like voltage drop, leakage currents or switching control we start checking power muxes as TPS2115A, but, when we were reading datasheet some doubts come to us about how this chip works.

First of all, does TPS21115A have Switchover time seamless features?

Type A:

Type B:

We don’t understand what the final assembly is, because figure 14 and 15 show pin D0 and pin D1 configuration for our type A and Type B circuit, but the following text say something different:

What is the correct configuration for Auto-Switching mode (with 2 different voltage)?

Is it possible to use Auto-Switching mode with Vin1=Vin2?

What is the correct configuration for Manual Switching mode with Vin1=Vin2?

 

Our second pack of doubts is about leakage and supply current for both configurations (type A and type B):

Case 1: When Vout -> Vin1 (Iout=0)     What is the consumption from IN1 and IN2?

Case 2: When Vout -> Vin2 (Iout=0):      What is the consumption from IN1 and IN2?

Reading datasheet we think that Iin1=55uA and Iin2=1uA at Case 1. And inverted at case 2. Correct?

Is there a chip whose consumption is lower? Because when MCU is on sleep mode, our Vout consumption is close to 10uA so if TPS5115A have a 55uA leakage, our total consumption is factor by 7 (almost 70uA), thats not acceptable.

As we comment before, type A configuration need a maximum of 200mA output current, so we can use TPS2114APW with Rlim=400ohm.

For type B we need 2A output current, so we must use TPS2115ADRB but, what is the Rlim value then?

 

 

  • 0
    TI__Genius 10855 points

    Hi Departamento,

    As mentioned in the other thread, I recommend taking a look at the TPS2121. The shutdown current of the device is 10uA typ., and provides a seamless switchover configuration to minimize the output voltage drop. The TPS2121 also goes up to 4.5A, with an adjustable current limit to set the max current to 2A.

    Thanks,

    Arthur Huang

    To find the latest information on Power Switches, visit www.ti.com/powerswitch

    Please click "This resolved my issue" button if this post answers your question.

  • 0 in reply to Alpha H
    Prodigy 90 points

    Hello Arthur,

    We have been checking TPS2121 datasheet and means really interesting, it might fit our features except for current consumption values.

    Following this table, we have 300uA when we are using a power source, and 15uA when this source is unused.

    Due to we need to reduce power consumption from both power sources (because we are powered by 2 batteries: Vin1 a main power battery, and Vin2 a back-up battery), we think that these values are not valid.

    TPS2115A have the following consumtion table:

    So, check it, consumption values seems to be smallers

    Tnak you so much.

  • 0 in reply to Adrian Cobos
    TI__Genius 10855 points

    Hi Departamento, 

    Thanks for the update. Please find the answers to your questions below:

    First of all, does TPS21115A have Switchover time seamless features?

    [AH]: Unfortunately, this device does not have seamless switchover functionality (the output voltage will drop slightly when switching between two inputs). You can look at Figure 6 on page 12 of the datasheet for a good representation of the voltage drop when switching between inputs. 

    What is the correct configuration for Auto-Switching mode (with 2 different voltage)? Is it possible to use Auto-Switching mode with Vin1=Vin2? What is the correct configuration for Manual Switching mode with Vin1=Vin2?

    [AH]: The figures on page 16 of the datasheet are correct, Figure 14 is for automatic switchover whereas Figure 15 is for Manual Switchover. If VIN1 = VIN2, then the device will prioritize IN1 (2nd row of the truth table). Therefore, automatic switchover will occur properly if both inputs are the same voltage. For manual switchover, if D1 is high the device will prioritize IN1 even if IN2 is higher. If D1 is low, the device will switchover to IN2. 

    Thanks,

    Arthur Huang

  • 0 in reply to Alpha H
    Prodigy 90 points

    Hello Arthur,

    We had read that TPS2115A have seamless features, the following extract appears in the datasheet:

    "The TPS211xA family of power multiplexers enables seamless transition between two power supplies (such as a battery and a wall adapter), each operating at 2.8 V to 5.5 V and delivering up to 2 A".

    Would you confirm it?

     

    Due to we are going to focus on Type A design:

    - Automatic and seamless power mux

    - With not iqual voltages batteries Vin1=5v and Vin2=3.3v

    - 200mA maximum continuous output current

    - Voltage drop not greater than 300mV

    Keeping in mind these requeriments, we are thinking on the following circuit:

     

    Is that asembly correct?

    Due to our both power sources, 5vdc and 3.3vdc comes from a different battery, we need to minimize power consumption on "operating" and "stand-by" of both cases.

    When VinX is connected to Vout (VinX operating), which have a 55uA leakage current, and VinY is off (Stand-by) with 1uA leakage current.

    Is there an option that has a lower leakage current in VinX (power in "operating")? Becasuse we have been finding out for alternatives, but we only have found greater currents

     

    In the case of maximum output current (200mA), TPS2115A has a maximum 110mohm resistance (with both 5vdc or 3.3vdc power supllies), so we might have a  22mV output voltage dropout per channel.

    That´s acceptable for us.

    Is that correct?

     

    Thank you for your attention.

  • 0 in reply to Adrian Cobos
    TI__Genius 10855 points

    Hi Deparmento, 

    The switchover time between inputs is 40us typ. Depending on your output loading conditions, this could cause the output voltage to droop, since this is the period of time where both inputs of the device will be off (due to make-before-break) conditions. You can read more about this condition in our new app note, Basics of Power MUX. 

    Unfortunately, there isn't an option that has lower leakage current. You could try a load switch configuration, like we discussed in the other thread, but none for our integrated solutions at this time. 

    Thanks,

    Arthur Huang