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, TPS826745, TPS826765
www.ti.com SLVSAI0F –OCTOBER 2010–REVISED NOVEMBER 2012
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. 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
loop response to change in V
O
is essentially instantaneous, which explains the transient response. Although this
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 17μA) 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 Links: TPS82670 TPS82671 TPS82672 TPS82673 TPS82674 TPS82675 TPS82676 TPS82677
TPS826711 TPS826745 TPS826765