Datasheet

ON
OUTIN
peakLPSM
t
L
VV
I ×
-
=
)(
)(
ns
V
V
t
IN
OUT
ON
400×=
TPS62130, TPS62130A
TPS62131, TPS62132, TPS62133
www.ti.com SLVSAG7B –NOVEMBER 2011–REVISED JUNE 2013
DETAILED DESCRIPTION
Device Operation
The TPS6213X synchronous switched mode power converters are based on DCS-Control™ (Direct Control with
Seamless Transition into Power Save Mode), an advanced regulation topology, that combines the advantages of
hysteretic, voltage mode and current mode control including an AC loop directly associated to the output voltage.
This control loop takes information about output voltage changes and feeds it directly to a fast comparator stage.
It sets the switching frequency, which is constant for steady state operating conditions, and provides immediate
response to dynamic load changes. To get accurate DC load regulation, a voltage feedback loop is used. The
internally compensated regulation network achieves fast and stable operation with small external components
and low ESR capacitors.
The DCS-Control
TM
topology supports PWM (Pulse Width Modulation) mode for medium and heavy load
conditions and a Power Save Mode at light loads. During PWM, it operates at its nominal switching frequency in
continuous conduction mode. This frequency is typically about 2.5MHz with a controlled frequency variation
depending on the input voltage. If the load current decreases, the converter enters Power Save Mode to sustain
high efficiency down to very light loads. In Power Save Mode the switching frequency decreases linearly with the
load current. Since DCS-Control
TM
supports both operation modes within one single building block, the transition
from PWM to Power Save Mode is seamless without effects on the output voltage.
Fixed output voltage versions provide smallest solution size and lowest current consumption, requiring only 3
external components. An internal current limit supports nominal output currents of up to 3A.
The TPS6213X family offers both excellent DC voltage and superior load transient regulation, combined with
very low output voltage ripple, minimizing interference with RF circuits.
Pulse Width Modulation (PWM) Operation
The TPS6213X operates with pulse width modulation in continuous conduction mode (CCM) with a nominal
switching frequency of 2.5 MHz or 1.25MHz, selectable with the FSW pin. The frequency variation in PWM is
controlled and depends on V
IN
, V
OUT
and the inductance. The device operates in PWM mode as long the output
current is higher than half the inductor's ripple current. To maintain high efficiency at light loads, the device
enters Power Save Mode at the boundary to discontinuous conduction mode (DCM). This happens if the output
current becomes smaller than half the inductor's ripple current.
Power Save Mode Operation
The TPS6213X's built in Power Save Mode will be entered seamlessly, if the load current decreases. This
secures a high efficiency in light load operation. The device remains in Power Save Mode as long as the inductor
current is discontinuous.
In Power Save Mode the switching frequency decreases linearly with the load current maintaining high efficiency.
The transition into and out of Power Save Mode happens within the entire regulation scheme and is seamless in
both directions.
TPS6213X includes a fixed on-time circuitry. This on-time, in steady-state operation, can be estimated as:
(1)
For very small output voltages, an absolute minimum on-time of about 80ns is kept to limit switching losses. The
operating frequency is thereby reduced from its nominal value, which keeps efficiency high. Using t
ON
, the typical
peak inductor current in Power Save Mode can be approximated by:
(2)
When V
IN
decreases to typically 15% above VOUT, the TPS6213X won't enter Power Save Mode, regardless of
the load current. The device maintains output regulation in PWM mode.
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Product Folder Links: TPS62130, TPS62130A TPS62131 TPS62132 TPS62133