SSL0004-ANE
2012-12-13
Rev.1.2
1
TOSHIBA Semiconductor Application Note
Load-Switch IC
1. Introduction
The load-switch IC consists of an output transistor and driving circuit in a single chip.
Usage of the load-switch IC can be found in the following application:
●Smartphone ●Mobile phone ●Tablet ●Digital camera
●Portable gaming device ●Notebook PC and accessories ●Portable AV equipment etc.
Particularly, it is used to meet the need for small discrete devices in smartphone, tablets
where there are strict power requirements, and performance is important. Also, a range of power
management devices are required.
To respond to these needs, multiple power supply ICs have been offered in a single power
supply IC (Power Management IC; PM-IC), however, as newer smartphone and tablets have
better specification and contain increasing number of functions, the number of channels and
power supply quality of the PM-IC may not suffice. In such case, the load-switch IC can
supplement the PM-IC.
The load-switch circuit normally comprises of discrete MOSFETs, however as the load-switch
IC can replace the multiple devices needed in discrete circuits, it saves space, and yet provides
additional function to which a discrete MOSFET circuit cannot provide. It is highly suitable as a
simple power management solution for complex systems.
Load-switch ICs have the following merits as compared to discrete circuits.
●Less devices thus saving space
●Over temperature protection, over current protection and other protection features
●Inrush current reduction and power supply sequence control reducing circuit design work
●Low drive voltage guarantee
●Full temperature range guarantee
This application note will introduce the load-switch IC and its basic circuit. We hope that you
will find it useful.
SSL0004-ANE
2012-12-13
Rev.1.2
2
2. Load-switch IC basics
The following section explains the basics of load-switch ICs.
●Load-switch IC basic circuit
The load-switch IC basic circuit is as shown in Fig.1
Load-switch IC is connected to the power supply with the input pin V
IN
, connected to the load
at the output pin V
OUT
, and has a CONTROL pin (Also known as Shutdown pin, Enable pin) with
logic control to turn the load-switch IC ON/OFF. The output voltage V
OUT
depends on the input
voltage V
IN
and the corresponding equivalent load resistance R
L
and thus output current I
LOAD
, the
output voltage is then the input voltage minus the dropout voltage due to the internal resistance of
the output transistor element in the load-switch IC and the output current.
Output voltage V
OUT
= Input voltage V
IN
―
( Output current I
LOAD
× Resistance of output transistor )
Generally, compared to the output transistor used in LDO regulator (Low Drop-out regulator,
LDO) IC, a rather low resistance transistor is used, so it can be used from the comparatively low
load of under 100mA to applications that require up to 500mA and above.
The power supply source is usually a lithium ion battery or the output of a PM-IC. Especially
for switching power supplies using a PM-IC at the input voltage VIN, there is likely to be noise
(ripple). The ideal power supply is to use an LDO to remove this noise, but as mentioned above,
LDO is usually limited to light load applications and require high input voltage. (For more details
on LDO, please refer to our LDO application note) The load-switch IC uses the power supply as it
is and only acts as a switch for the load, thus it does not remove any noise. For stability it is
recommended that an input capacitor C
IN
be used. Also, load-switch ICs typically have various
embedded additional functions, depending on the product type. These functions and the block
diagrams will be explained with Toshiba’s TCK10xG series as an example below.
Power
supply
CONTROL
Fig.1 Basic load-switch IC example
V
IN
V
OUT
GND
Equivalent
Capacitance
C
L
Equivalent
Resistance
R
L
Load
High
Low
Load-switch IC
Input capacitor
C
IN
I
LOAD