TPS40090-Q1

www.ti.com

SLUS845C

– JUNE 2008 – REVISED MAY 2011

APPLICATION INFORMATION

Functional Description

The TPS40090 is a multiphase, synchronous, peak current mode, buck controller. The controller uses external

gate drivers to operate N-channel power MOSFETs. The controller can be configured to operate in a two-, three-,

or four-phase power supply.

The controller accepts current feedback signals from either current sense resistors placed in series with the filter

inductors or current proportional signals derived from the inductors' DCR.

Other features include an LDO regulator with UVLO to provide single voltage operation, a differential input

amplifier for precise output regulation, user programmable operation frequency for design flexibility, external

synchronization capability, programmable pulse-by-pulse overcurrent protection, output overvoltage protection,

and output undervoltage shutdown.

Differential Amplifier

The unity gain differential amplifier with high bandwidth allows improved regulation at a user-defined point and

eases layout constraints. The output voltage is sensed between the VOUT and GNDS pins. The output voltage

programming divider is connected to the output of the amplifier (DIFFO). The differential amplifier can be used

only for output voltages lower then 3.3 V.

If there is no need for a differential amplifier, or if the output voltage required is higher than 3.3 V, the differential

amplifier can be disabled by connecting the GNDS pin to the BP5 pin. The voltage programming divider in this

case should be connected directly to the output of the converter.

Current Sensing and Balancing

The controller employs a peak current-mode control scheme, which naturally provides a certain degree of current

balancing. With current mode, the level of current feedback should comply with certain guidelines depending on

duty factor, known as slope compensation to avoid subharmonic instability. This requirement can prohibit

achieving a higher degree of phase current balance. To avoid the controversy, a separate current loop that

forces phase currents to match is added to the proprietary control scheme. This effectively provides high degree

of current sharing independently of properties of controller's small signal response.

High-bandwidth current amplifiers can accept as an input voltage either voltage drop across dedicated precise

current-sense resistors, or inductor's DCR voltage derived by an R-C network, or thermally compensated voltage

derived from the inductor's DCR. The wide range of current-sense settings eases the cost and complexity

constraints and provides performance superior to those found in controllers using low-side MOSFET current

sensing.

Copyright

© 2008–2011, Texas Instruments Incorporated

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