Push Button Load Switch

In this article we discuss how to implement “Shutdown Mode” to disconnect the battery from the system if the Power Management IC (PMIC) you have selected does not include this feature.

In many applications there are benefits to be gained by disconnecting the battery from the system.  In the past you would sometimes see this implemented with a simple plastic pull tab, that would be placed between the battery and battery terminal when the product was manufactured, prior to shipping (see Fig.1).  This allowed the battery to remain disconnected during shipment and whilst it sat on the retailer’s shelves. 

 

(Fig.1: Plastic spacer used to disconnect a battery during shipping and storage)

 

When the user bought the product and opened the box, they would simply remove the plastic spacer by pulling on the tab to re-establish the connection between the battery and battery terminal.  This was easy and cheap to implement with older batteries, but unfortunately it is not possible to do the same with newer Li-Ion or Li-Polymer batteries which often need to be enclosed so the user cannot access them for safety reasons. 

However, we can recreate this functionality by adding our XC6193 Push Button Load Switch between the battery and the main power circuit or between the battery and the MCU if the MCU is connected directly to the battery without any power circuit.  It is possible to completely shut the line from the battery, which in turn stops the battery draining over time and we call this function “Ship Mode” or “Shutdown Mode”.   In our tests we have seen that over a period of 6 months in storage, the difference in remaining battery life comparing applications with/without the Load Switch is significant (see Fig.2).

 

(Fig.2: Advantage of Storage Mode)

 

In the circuit below (Fig.3), you can see how our XC6193 can be used to implement “Shutdown Mode” by placing the XC6193 and it’s external Pch SW between the BAT pin of PMIC and battery.

 

(Fig.3: Circuit for implementing “Shutdown Mode” with the XC6193)

 

When implementing this circuit, please consider the following points:

• Please do not connect the VOUT pin of XC6193 to the BAT rail.  The VOUT pin has a CL discharge SW inside and it will prevent XC6193 from starting up when the Li battery is at over discharge status because the current from Charge is not so large at over discharge situation.
• The SBD1 connected to Pch SW in parallel is for starting up at over discharge situation.
• Please be careful when connecting the Pch SW, the source is to the battery and the drain is to the BAT rail.

 

The quiescent current for the XC6193 is only 0.13µA (TYP.) and during Stand-by this reduces to 0.001µA (TYP.). It is available in the ultra-small USP-8B06 package which measures 2.0mm x 2.0mm x 0.33mm, so in can be implemented with a small PCB area.

To avoid inrush current during start up the XC6193 uses the internal switch between VIN and VOUT. Once the voltage has increased to a suitable level, the external MOSFET is turned on. This avoids a large inrush current being drawn from the battery and helps avoid depletion.

 

Samples of the XC6193 series are readily available, so please ask your local Torex representative for details or contact us directly via our website.  We can also supply populated evaluation boards upon request.

If you would like to know more about our range of Push Button Load Switches and about the benefits of “Shutdown Mode” please click here.