Why is my tablet not charging in Simulcharge Mode?

This article discusses issues for all STS-** products, the TL002, and the STS OEM board.

The most common reasons a tablet does not charge in SimulCharge mode include:

  • Power supply is not DCP (only a TL002 issue)
  • Reverse tablet and power connections on the STS**/TL002
  • STS** configuration not set for tablet being used (see TYPE jumper in User Manual)
  • Power supply not delivering proper voltage to STS/TL002 input
  • Cable connecting STS**/TL002 to the tablet is not the one provided by LAVA
  • Power supply connected to STS** before, STS** was attached to tablet
  • Tablet internal devices still active which are not required
  • Tablet application(s) may be consuming excessive processor time
  • Tablet screen is too bright (some tablets cannot be run at full brightness)
  • Tablet is not from the list of supported devices
  • Tablet is from region which does not include SimulCharge
  • Tablet is not a Samsung tablet
  • USB accessory drawing too much power
  • Faulty cable connecting STS**/TL002 to tablet
  • Faulty STS**/TL002

A LAVA TL002 requires a USB Power Supply with a Direct Charge Port (DCP). A DCP supply has the two USB data pins shorted together to identify it as a high capacity power supply to the device it is plugged into. The USB power supply shipped with each Samsung tablet is a DCP supply. For initial testing always use the power supply provided with the tablet, to establish a baseline.

The “to tablet” and “power in” receptacles on the STS**/TL002 devices are both Micro USB-B receptacles. It is very easy to get the connections backward. The STS** devices will actually partially power up suggesting the device is working. The Charge-Only light will flash for the expected 2 to 3 seconds, and then the SimulCharge light will come on.

The revision 2 STS** devices (units made after November 2015) have and internal TYPE jumper that has to be set for the intended tablet. The “STS Product Family – User Manual” describes the STS** setup issues and features. This jumper is not installed as a manufacturing default, which allows the STS** to work with newer tablets. This jumper must be installed for older tablets such as Tab 4, Tab S, Tab Pro, and Tab Note Pro. The revision one products are only meant for the older tablets. The correct jumper setting is critical for the Tab S2 and Tab 4 products.

The STS**/TL002 power input should not be below 5 volts, with a preferred range of 5.1 to 5.25 volts. Although the system may appear to work with a lower voltage, a variety of problems are going to occur. The power supply capacity (i.e., current rating in amperes) must be adequate for the STS**, tablet, and attached accessories. If the power supply capacity is too low, it may shut down, or produce a low voltage. The STS**/TL002 input voltage must be tested for a tablet with the battery at minimum charge and close to full charge. If the STS**/TL002 input voltage is too low, it must be resolved before proceeding.

The STS** products using PoE eliminate some power supply issues, as an internal supply voltage is generated from power provided over the Ethernet cable.

The cable which connects the STS**/TL002 to the tablet is critical. Do not replace the cable provided by LAVA. Do not extend the cable provided by LAVA. If you have replaced or extended the cable, go back to the original cable to see if this is the source of the problems.  Changing the cable can result in voltage drop problems, hence poor charging or no charging. Changing the cable may result in the tablet not entering SimulCharge mode at all, hence no USB accessories and no charging.

The STS** is to be connected to the tablet before power is applied to the STS** device. This allows the STS** to apply signals to the tablet in the correct order to reliably enter SimulCharge mode. If the order is reversed, some tablets may not enter SimulCharge mode, hence may not charge and may not recognize USB accessories. The fix is to simply remove power and restore power.

Verify that applications running on the tablet are not consuming an excessive amount of processor time. Application components running every few milliseconds may have to be slowed down. Intense screen animations may have to be reviewed. Any background services in use must be reviewed. Application processor time in Android adds to the power used and for limited input power, results in reduced battery charging capability.

Built-in devices (e.g., WiFi, GPS) that are not required should be disabled to reduce power requirements.

With the power supply and cabling issues resolved, the tablet battery may still not charge. Lower the screen brightness to 25% and check for battery charging. From the 25% level, work your way up to see how bright the screen can be. High-resolution tablets and tablets with large screens consume significant power.

A tablet in SimulCharge mode restricts the current it will draw from the power supply, which indirectly limits how bright the screen can be.

The color scheme used by your application affects the screen power requirements. A screen that is predominantly white requires more power than one that is mainly black. A high contrast scheme that keeps the background elements darker helps to reduce power requirements. This can tip the balance in some cases to allow a battery to charge. A revised color scheme may allow the brightness to be increased.

If the tablet being used is not from the list of supported devices, there may be fundamental issues with it. The most serious issue may be it lacks SimulCharge support. Many of the special tablet version created for Mobile Carriers remove wired Ethernet support and SimulCharge. While the two features need not be tied together, then commonly are. If the tablet lacks the internal support, there are no practical options for most people. If you are working on a high profile project with a large number of tablets, it may be possible to work with Samsung to change the features in the tablet.

There are many variations of each tablet model based on the region in which it is sold. In some regions, the SimulCharge feature may simply not be available. In most cases, the only way to determine this is to try the tablet in question.

The STS** devices are only designed to work with select Samsung tablets. Although we state this clearly, people have occasionally tried to use an STS** device on another manufacturer tablet. If you are developing custom tablet firmware on a rooted tablet, then the possibilities change.

When using USB accessories, you must ensure the rating of the power supply used can handle the STS**, the tablet, and attached accessories. Unplug the accessory and verify the system behavior to determine if the problems are due to the attached device.

It is possible for the cable which connects the STS**/TL002 to be bad. The junction point in the sealed case may have broken lose. Trying a second cable is required to confirm this.

When power is applied to the STS** the indicator lights have a distinctive pattern as described in the user manual. If the power supply is good and these lights fail, the STS** will have to be returned for repair.

The Micro USB-B receptacles are not as robust as the USB-A receptacles. If the cable was pushed in upside down, the receptacle might have been damaged. It is possible the faulty receptacle to look intact, but one or more connections may be broken. The Micro USB-B receptacles used on LAVA products were changed in 2015 to use a part which is secured more firmly to the board and is better protected against a cable being pushed in too hard.

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