TPS65257_15 Datasheet, PDF (1/35 Pages) Texas Instruments – 4.5-V TO 16-V INPUT, HIGH CURRENT, SYNCHRONOUS STEP DOWN THREE DC-DC CONVERTER WITH INTEGRATED FET, USB SWITCH AND PUSH BUTTON CONTROL

TPS65257
www.ti.com
SLVSB32A – SEPTEMBER 2011 – REVISED DECEMBER 2012
4.5-V TO 16-V INPUT, HIGH CURRENT, SYNCHRONOUS STEP DOWN THREE DC-DC
CONVERTER WITH INTEGRATED FET, USB SWITCH AND PUSH BUTTON CONTROL
Check for Samples: TPS65257
FEATURES
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• Wide Input Supply Voltage Range:
4.5 V - 16 V
• 0.8-V, 1% Accuracy Reference
• Continuous Loading:
3 A (Buck1), 2 A (Buck2 and 3)
• Maximum Current:
3.5 A (Buck 1), 2.5 A (Buck2 and 3)
• Synchronous Operation, 300-kHz – 2.2-MHz
Switching Frequency Set By External Resistor
• External Enable Pins With Built-In Current
Source for Easy Sequencing
• External Soft Start Pins
• Adjustable Cycle-by-Cycle Current Limit Set
by External Resistor
• Current-Mode Control With Simple
Compensation Circuit
• Automatic Low Pulse Skipping (PSM) Power
Mode, Allowing for an Output Ripple Better
than 2%
• Support Pre-Biased Outputs
• Power Good Supervisor and Reset Generator
• 1-A USB Power Switch With Overcurrent and
Thermal Protection
• Push Button (10-kV ESD Rated Pin for PB_IN)
Control for Intelligent System Power-
On/Power-Off Operation
• Small, Thermally Efficient 40-Pin 6-mm x 6-mm
RHA (QFN) package
• -40°C to 125°C Junction Temperature Range
DESCRIPTION/ORDERING INFORMATION
TPS65257 is a power management IC with three step-down buck converters. Both high-side and low-side
MOSFETs are integrated to provide fully synchronous conversion with higher efficiency. The converters are
designed to simplify its application while giving the designer the option to optimize their usage according to the
target application.
The converters can operate in 5-, 9-, 12- or 15-V systems. The output voltage can be set externally using a
resistor divider to any value between 0.8 V and the input supply minus the resistive drops on the converter path.
Each converter features enable pin that allows a delayed start-up for sequencing purposes, soft start pin that
allows adjustable soft-start time by choosing the soft-start capacitor, and a current limit (RLIM) pin that enables
designer to adjust current limit by selecting an external resistor and optimize the choice of inductor. All converters
operate in ‘hiccup mode’: Once an over-current lasting more than 10 ms is sensed in any of the converters, they
will shut down for 10 ms and then the start-up sequencing will be tried again. If the overload has been removed,
the converter will ramp up and operate normally. If this is not the case the converter will see another over-current
event and shuts down again repeating the cycle (hiccup) until the failure is cleared. If an overload condition lasts
for less than 10 ms, only the relevant converter affected will shut-down and re-start and no global hiccup mode
will occur.
The switching frequency of the converters is set by an external resistor connected to ROSC pin. The switching
regulators are designed to operate from 300 kHz to 2.2 MHz. The converters operate with 180° phase between
then to minimize the input filter requirements.
All converters have peak current mode control which simplifies external frequency compensation. The device has
a built-in slope compensation ramp. The slope compensation can prevent sub harmonic oscillations in peak
current mode control. A traditional type II compensation network can stabilize the system and achieve fast
transient response. Moreover, an optional capacitor in parallel with the upper resistor of the feedback divider
provides one more zero and makes the crossover frequency over 100 kHz.
All converters feature an automatic low power pulse PFM skipping mode which improves efficiency during light
loads and standby operation, while guaranteeing a very low output ripple, allowing for a value of less than 2% at
low output voltages.
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Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2011–2012, Texas Instruments Incorporated