TPS2500 datasheet(11/43 Pages) TI2

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TJ − Junction Temperature − °C

−50

100

150

G007

VIN = 3.3 V

VIN − Input Voltage − V

G008

TJ = −40°C

TJ = 85°C

TJ = 25°C

TPS2500, TPS2501

www.ti.com

SLVS886C – OCTOBER 2008 – REVISED AUGUST 2010

TYPICAL CHARACTERISTICS (continued)

Figure 9. Bias Current vs Junction Temperature,

Figure 10. Bias Current vs Input Voltage,

VIN = 3.3 V, VEN = 0 V (Disabled)

VEN = 0 V (Disabled)

THEORY OF OPERATION

DESCRIPTION

This device targets applications for host-side USB devices where a 5-V power rail, required for USB operation, is

unavailable. The TPS2500 integrates the functionality of a synchronous boost converter and a single USB switch

into a monolithic integrated circuit so that lower-voltage rails can be used directly to provide USB power. An

additional feature is that the auxiliary 5-V power rail is brought external to the device to power non-USB loads in

addition to the integrated USB switch.

The boost converter is highly integrated, including the switching MOSFETs (low-side N-channel, high-side

synchronous P-channel), gate-drive and analog-control circuitry, and control-loop compensation. Additional

features include high-efficiency light-load operation, overload and short-circuit protection, and controlled

monotonic soft start. The USB switch integrates all necessary functions, including back-to-back series N-channel

MOSFETs, charge-pump gate driver, and analog control circuitry. The current-limit protection is user-adjustable

by selecting the RILIM resistor from ILIM to GND.

The only external components required are the boost inductor, current-limit setting resistor, and input and output

capacitors for the boost converter.

BOOST CONVERTER

Start-Up

Input power to the TPS2500 is provided from IN to GND. The device has an undervoltage lockout (UVLO) circuit

that disables the device until the voltage on IN exceeds 2.15 V (typical). The TPS2500 goes through its normal

start-up process and attempts to regulate the AUX voltage to 5.1 V (typical).

The boost converter has a two-step start-up sequence. Step one is a constant-current mode that regulates the

current through the high-side P-channel MOSFET to ISTART (2.65 A typical). ISTART provides power to the load and

charges the output capacitance on VAUX until VAUX reaches VIN – VEXIT. The converter begins to switch once VAUX

exceeds VIN – VEXIT. The initial duty cycle of the device is limited by a closed-loop soft start that ramps the

reference voltage to the internal error amplifier to provide a controlled, monotonic start-up on VAUX. The boost

converter goes through this cycle any time the voltage on VAUX drops below VIN – VEXIT due to overload

conditions or the boost converter re-enables after normal shutdown.

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