Datasheet

PFMModeatLightLoad
PFMRipple
PWMModeatHeavyLoad
NominalDCOutputVoltage
TPS82670 , TPS82671 , TPS82672 , TPS82673 , TPS82674 , TPS82675
TPS82676 , TPS82677 , TPS826711 , TPS826721 , TPS826745 , TPS826765
SLVSAI0H –OCTOBER 2010–REVISED OCTOBER 2014 www.ti.com
9.3 Feature Description
9.3.1 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 7. Operation In PFM Mode And Transfer To PWM Mode
9.3.2 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.
For additional flexibility, it is possible to switch from power-save mode to PWM mode during operation. This type
of operation allows efficient power management by adjusting the operation of the converter to the specific system
requirements.
9.3.3 Spread Spectrum, PWM Frequency Dithering
The goal of spread spectrum architecture is to spread out the emitted RF energy over a larger frequency range
so that any resulting electromagnetic interference (EMI) is similar to white noise. The end result is a spectrum
that is continuous and lower in peak amplitude. Spread spectrum makes it easier to comply with EMI standards.
It also makes it easier to comply with the power supply ripple requirements in cellular and non-cellular wireless
applications. Radio receivers are typically susceptible to narrowband noise that is focused on specific
frequencies.
Switching regulators can be particularly troublesome in applications where electromagnetic interference (EMI) is
a concern. Switching regulators operate on a cycle-by-cycle basis to transfer power to an output. In most cases,
the frequency of operation is either fixed or regulated, based on the output load. This method of conversion
creates large components of noise at the frequency of operation (fundamental) and multiples of the operating
frequency (harmonics).
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