PFMModeatLightLoad

PFMRipple

PWMModeatHeavyLoad

NominalDCOutputVoltage

TPS82671, TPS82672, TPS82675

TPS82676, TPS82677

SLVSAI0C

– OCTOBER 2010 – REVISED NOVEMBER 2011

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DETAILED DESCRIPTION

OPERATION

The TPS8267x is a stand-alone, synchronous, step-down converter. The converter operates at a regulated

5.5-MHz frequency pulse width modulation (PWM) at moderate to heavy load currents (up to 600mA output

current). At light load currents, the TPS8267x converter operates in power-save mode with pulse frequency

modulation (PFM).

The converter uses a unique frequency-locked ring-oscillating modulator to achieve best-in-class load and line

response. One key advantage of the non-linear architecture is that there is no traditional feed-back loop. The

type of operation normally results in a switching frequency that varies with input voltage and load current, an

internal frequency lock loop (FLL) holds the switching frequency constant over a large range of operating

conditions.

Combined with best-in-class load and line-transient response characteristics, the low quiescent current of the

device (approximately 17

μA) helps to maintain high efficiency at light load while that current preserves a fast

transient response for applications that require tight output regulation.

The TPS8267x integrates an input current limit to protect the device against heavy load or short circuits and

features an undervoltage lockout circuit to prevent the device from misoperation at low input voltages. Fully

functional operation is permitted down to 2.1V input voltage.

POWER-SAVE MODE

If the load current decreases, the converter enters power-save mode automatically. During power-save mode,

the converter operates in discontinuous current, (DCM) single-pulse PFM mode, which produces a low output

ripple compared with other PFM architectures.

When in power-save mode, the converter resumes its operation when the output voltage falls below the nominal

voltage. The converter ramps up the output voltage with a minimum of one pulse and goes into power-save

mode when the output voltage is within its regulation limits.

The IC exits PFM mode and enters PWM mode when the output current can no longer be supported in PFM

mode. As a consequence, the DC output voltage is typically positioned approximately 0.5% above the nominal

output voltage. The transition between PFM and PWM is seamless.

Figure 40. Operation in PFM Mode and Transfer to PWM Mode

MODE SELECTION

The MODE pin selects the operating mode of the device. Connecting the MODE pin to GND enables the

automatic PWM and power-save mode operation. The converter operates in regulated frequency PWM mode at

moderate to heavy loads, and operates in PFM mode during light loads. This type of operation maintains high

efficiency over a wide load current range.

Pulling the MODE pin high forces the converter to operate in PWM mode even at light-load currents. The

advantage is that the converter modulates its switching frequency according to a spread spectrum PWM

modulation technique that allows simple filtering of the switching harmonics in noise-sensitive applications. In this

mode, the efficiency is lower when compared to the power-save mode during light loads.

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Product Folder Link(s): TPS82671 TPS82672 TPS82675 TPS82676 TPS82677