Datasheet

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T -JunctionTemperature-°C
J
V =5V
I
RDSON-StaticDrain-SourceOn-StateResistance- W
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T - Junction Temperature - °C
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Vin = 5 V,
SS = 0.4 V
SSTR - Vsense Offset - mV
TPS57112-Q1
www.ti.com SLVSAL8 –DECEMBER 2010
TYPICAL CHARACTERISTICS CURVES (continued)
PWRGD ON-RESISTANCE vs TEMPERATURE SS/TR to VSENSE OFFSET vs TEMPERATURE
Figure 19. Figure 20.
OVERVIEW
The TPS57112-Q1 is a 6-V, 2-A, synchronous step-down (buck) converter with two integrated n-channel
MOSFETs. To improve performance during line and load transients the device implements a constant frequency,
peak current mode control which reduces output capacitance and simplifies external frequency compensation
design. The wide switching frequency of 200 kHz to 2000 kHz allows for efficiency and size optimization when
selecting the output filter components. The switching frequency is adjusted using a resistor to ground on the
RT/CLK pin. The device has an internal phase lock loop (PLL) on the RT/CLK pin that is used to synchronize the
power switch turn on to a falling edge of an external system clock.
The TPS57112-Q1 has a typical default start up voltage of 2.45 V. The EN pin has an internal pull-up current
source that can be used to adjust the input voltage under voltage lockout (UVLO) with two external resistors. In
addition, the pull up current provides a default condition when the EN pin is floating for the device to operate.
The total operating current for the TPS57112-Q1 is typically 515 mA when not switching and under no load.
When the device is disabled, the supply current is less than 5.5 mA.
The integrated 12 mΩ MOSFETs allow for high efficiency power supply designs with continuous output currents
up to 2 A.
The TPS57112-Q1 reduces the external component count by integrating the boot recharge diode. The bias
voltage for the integrated high side MOSFET is supplied by a capacitor between the BOOT and PH pins. The
boot capacitor voltage is monitored by an UVLO circuit and turns off the high side MOSFET when the voltage
falls below a preset threshold. This BOOT circuit allows the TPS57112-Q1 to operate approaching 100%. The
output voltage can be stepped down to as low as the 0.800 V reference.
The TPS57112-Q1 has a power good comparator (PWRGD) with 2% hysteresis.
The TPS57112-Q1 minimizes excessive output overvoltage transients by taking advantage of the overvoltage
power good comparator. When the regulated output voltage is greater than 109% of the nominal voltage, the
overvoltage comparator is activated, and the high side MOSFET is turned off and masked from turning on until
the output voltage is lower than 107%.
The SS/TR (slow start/tracking) pin is used to minimize inrush currents or provide power supply sequencing
during power up. A small value capacitor should be coupled to the pin for slow start. The SS/TR pin is
discharged before the output power up to ensure a repeatable restart after an overtemperature fault, UVLO fault
or disabled condition.
The use of a frequency fold-back circuit reduces the switching frequency during startup and over current fault
conditions to help limit the inductor current.
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Product Folder Link(s): TPS57112-Q1