TPS54227_15 Datasheet, PDF (8/24 Pages) Texas Instruments – Synchronous Step-Down Converter

TPS54227
SLVSAU2C – MAY 2011 – REVISED DECEMBER 2015
7 Detailed Description
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7.1 Overview
The TPS54227 is a 2-A synchronous step-down (buck) converter with two integrated N-channel MOSFETs. It
operates using D-CAP2 mode control. The fast transient response of D-CAP2 control reduces the output
capacitance required to meet a specific level of performance. Proprietary internal circuitry allows the use of low
ESR output capacitors including ceramic and special polymer types.
7.2 Functional Block Diagram
EN
EN
1
Logic
SGND
PGND
VFB
2
VREG5
3
SS
4
Ref +
SS
+PWM
-
SS
Softstart
SGND
Control Logic
VREG5
1 shot
XCON
ON
VREG5
VIN
VIN
8
VBST
7
SW
VO
6
Ceramic
Capacitor
5
GND
+
OCP
-
SW
PGND
VIN
VREG5
REF
UVLO
Ref
UVLO
TSD
Protection
Logic
7.3 Feature Description
7.3.1 PWM Operation
The main control loop of the TPS54227 is an adaptive ON-time pulse width modulation (PWM) controller that
supports a proprietary D-CAP2 mode control. D-CAP2 mode control combines constant ON-time control with an
internal compensation circuit for pseudo-fixed frequency and low external component count configuration with
both low ESR and ceramic output capacitors. It is stable even with virtually no ripple at the output.
At the beginning of each cycle, the high-side MOSFET is turned on. This MOSFET is turned off after internal one
shot timer expires. This one shot is set by the converter input voltage, VIN, and the output voltage, VO, to
maintain a pseudo-fixed frequency over the input voltage range, hence it is called adaptive ON-time control. The
one-shot timer is reset and the high-side MOSFET is turned on again when the feedback voltage falls below the
reference voltage. An internal ramp is added to reference voltage to simulate output ripple, eliminating the need
for ESR induced output ripple from D-CAP2 mode control.
8
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