Datasheet

SLVA037A
Designing a USB Power Distribution System Using the TPS2014 and TPS2015 Power Distribution Switches
3
1 Introduction
The universal serial bus (USB) interface is a 12-Mb/s, multiplexed serial bus designed for low to
medium speed PC peripherals (for example, keyboards, printers, scanners). The four-line USB
interface is conceived for dynamic attach-detach (hot-plug-unplug) of peripheral devices. Two
lines are provided for differential data and two lines are provided for 5-V power distribution.
USB data is a 3.3-V level signal, but power is distributed at 5 V to allow for voltage drops in
cases where power is distributed through more than one hub. Each function must provide its
own regulated 3.3 V from the 5-V input or its own internal power supply.
The USB specification defines the following five classes of devices, each differentiated by power
sourcing and sinking requirements:
• Bus-powered hubs
• Self-powered hubs
• Low power, bus-powered functions
• High power, bus-powered functions
Self-powered and bus-powered hubs distribute data and power to downstream functions. This
application report describes power distribution solutions for both types of hubs.
2 TPS2014 and TPS2015 Power Distribution Switches
The Texas Instruments TPS2014 and TPS2015 are high-side, 95-mΩ, n-channel MOSFET
switches with built-in overcurrent protection. The switches provide both power switching and
maintenance-free fault protection in either of the following single 8-pin packages:
• Small-outline integrated circuit (SOIC)
• Plastic dual inline package (PDIP)
The TPS2014 and TPS2015 switches differ only in recommended continuous current and short-
circuit current limits (see Table 1).
Table 1. TPS2014 and TPS2015 Current Limits
RECOMMENDED MAXIMUM TYPICAL SHORT-CIRCUIT PACKAGED DEVICES
T
j
CONTINUOUS LOAD CURRENT
(A)
CURRENT LIMIT AT 25
O
C
(A)
SOIC
(D)
+
PDIP
(P)
0
O
C to 125
O
C 0.6 1.2 TPS2014D TPS2014P
0
O
C to 125
O
C 1 2 TPS2015D TPS2015P
* The D package is available taped and reeled. Add an R suffix to device type (e.g. TPS2014DR).
Both devices are controlled by a logic level enable that is compatible with both 3.3-V and 5-V
logic. Gate drive is provided by an internal charge pump controls the power switch rise and fall
times to minimize currents during switching. The charge pump requires no external components
and operates from supply voltages as low as 4 V. The undervoltage lockout ensures that the
switch is in the off state at start up.