Datasheet

ON
OUTIN
peakLPSM
t
L
VV
I ×
-
=
)(
)(
ns
V
V
t
IN
OUT
ON
400×=
TPS62140, TPS62140A
TPS62141, TPS62142, TPS62143
www.ti.com SLVSAJ0B –NOVEMBER 2011–REVISED JUNE 2013
DETAILED DESCRIPTION
Device Operation
The TPS6214X 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 with 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 topology supports pulse-width modulation (PWM) 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 2.5 MHz 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.
Because DCS-Control 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 the smallest solution size and lowest current consumption, requiring only 3
external components. An internal current limit supports nominal output currents of up to 2A.
The TPS6214X 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 TPS6214X operates with pulse-width modulation in continuous-conduction mode (CCM) with a nominal
switching frequency of 2.5 MHz or 1.25 MHz, 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 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 ripple current.
Power-Save Mode Operation
The TPS6214X enters its built-in power-save mode 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.
TPS6214X includes a fixed-on-time circuit. The on-time, in steady-state operation, can be estimated as:
(1)
For very small output voltages, an absolute minimum on-time of about 80 ns 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 TPS6214X does not enter power-save mode, regardless
of the load current. The device maintains output regulation in PWM mode.
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Product Folder Links: TPS62140 TPS62140A TPS62141 TPS62142 TPS62143