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TPS63021DSJT Datasheet(PDF) 13 Page - Texas Instruments

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No. de Pieza. TPS63021DSJT
Descripción  HIGH EFFICIENCY SINGLE INDUCTOR BUCK-BOOST CONVERTER WITH 4-A SWITCHES
Descarga  24 Pages
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Fabricante  TI [Texas Instruments]
Página de inicio  http://www.ti.com
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TPS63021DSJT Datasheet(HTML) 13 Page - Texas Instruments

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TPS63020
TPS63021
www.ti.com
SLVS916 – APRIL 2010
DETAILED DESCRIPTION
CONTROLLER CIRCUIT
The controller circuit of the device is based on an average current mode topology. The average inductor current
is regulated by a fast current regulator loop which is controlled by a voltage control loop. The controller also uses
input and output voltage feedforward. Changes of input and output voltage are monitored and immediately can
change the duty cycle in the modulator to achieve a fast response to those errors. The voltage error amplifier
gets its feedback input from the FB pin. At adjustable output voltages, a resistive voltage divider must be
connected to that pin. At fixed output voltages, FB must be connected to the output voltage to directly sense the
voltage. Fixed output voltage versions use a trimmed internal resistive divider. The feedback voltage will be
compared with the internal reference voltage to generate a stable and accurate output voltage.
The controller circuit also senses the average input current. With this, maximum input power can be controlled to
achieve a safe and stable operation under all possible conditions. To protect the device from overheating, an
internal temperature sensor is implemented.
Synchronous Operation
The device uses 4 internal N-channel MOSFETs to maintain synchronous power conversion across all possible
operating conditions. This enables the device to keep high efficiency over a wide input voltage and output power
range.
To avoid ground shift problems due to the high currents in the switches, two separate ground pins GND and
PGND are used. The reference for all control functions is the GND pin. The power switches are connected to
PGND. Both grounds must be connected on the PCB at only one point, ideally, close to the GND pin. Due to the
4-switch topology, the load is always disconnected from the input during shutdown of the converter.
Buck-Boost Operation
To regulate the output voltage properly at all possible input voltage conditions, the device automatically switches
from step down operation to boost operation and back as required by the configuration. It always uses one active
switch, one rectifying switch, one switch permanently on, and one switch permanently off. Therefore, it operates
as a step down converter (buck) when the input voltage is higher than the output voltage, and as a boost
converter when the input voltage is lower than the output voltage. There is no mode of operation in which all 4
switches are permanently switching. Controlling the switches this way allows the converter to maintain high
efficiency at the most important point of operation, when input voltage is close to the output voltage. The RMS
current through the switches and the inductor is kept at a minimum to minimize switching and conduction losses.
Switching losses are kept low by using only one active and one passive switch. For the remaining 2 switches,
one is kept permanently on and the other is kept permanently off, thus causing no switching losses.
Power Save Mode and Synchronization
The PS/SYNC pin can be used to select different operation modes. To enable power save, PS/SYNC must be
set low. Power save mode is used to improve efficiency at light load. If power save mode is enabled, the
converter stops operating if the average inductor current goes lower than about 100 mA and the output voltage is
at or above its nominal value. If the output voltage decreases below its nominal value, the device ramps up the
output voltage again by starting operation using an average inductor current higher than required by the current
load condition. Operation can last for one or several pulses. The converter again stops operating once the
conditions for stopping operation are met again.
The power save mode can be disabled with a high at the PS/SYNC. Connecting a clock signal at PS/SYNC
forces the device to synchronize to the connected clock frequency. Synchronization is done by a PLL, so
synchronizing to lower and higher frequencies compared to the internal clock works without any issues. The PLL
can also tolerate missing clock pulses without the converter malfunctioning. The PS/SYNC input supports
standard logic thresholds.
Copyright © 2010, Texas Instruments Incorporated
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Product Folder Link(s): TPS63020 TPS63021


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