TPS54388-Q1_15 Datasheet, PDF (11/40 Pages) Texas Instruments – TPS54388-Q1 2.95-V to 6-V Input, 3-A Output, 2-MHz, Synchronous Step-Down SWIFT™ Switcher

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8 Detailed Description
TPS54388-Q1
SLVSAF1D – OCTOBER 2010 – REVISED APRIL 2015
8.1 Overview
The TPS54388-Q1 device is a 6-V, 3-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 range of 200 kHz to 2000 kHz allows for efficiency and size
optimization when selecting the output-filter components. A resistor to ground on the RT/CLK pin sets the
switching frequency. The device has an internal phase-lock loop (PLL) on the RT/CLK pin that synchronizes the
power-switch turnon to a falling edge of an external system clock.
The TPS54388-Q1 device has a typical default start-up voltage of 2.45 V. The EN pin has an internal pullup
current source that one can use to adjust the input-voltage undervoltage lockout (UVLO) with two external
resistors. In addition, the pullup current provides a default condition, allowing the device to operate when the EN
pin is floating. The total operating current for the TPS54388-Q1 device is typically 515 μA when not switching
and under no load. With the device disabled, the supply current is typically 5.5 μA.
The integrated 12-mΩ MOSFETs allow for high-efficiency power-supply designs with continuous output currents
up to 3 A.
The TPS54388-Q1 device reduces the external component count by integrating the boot recharge diode. A
capacitor between the BOOT and PH pins supplies the bias voltage for the integrated high-side MOSFET. A
UVLO circuit monitors the boot-capacitor voltage and turns off the high-side MOSFET when the voltage falls
below a preset threshold. This BOOT circuit allows the TPS54388-Q1 device to operate approaching 100% duty
cycle. The lower limit for stepping down the output voltage is the 0.8-V reference.
The TPS54388-Q1 device has a power-good comparator (PWRGD) with 2% hysteresis.
The TPS54388-Q1 device minimizes excessive output overvoltage transients by taking advantage of the
overvoltage power-good comparator. A regulated output voltage exceeding 109% of the nominal voltage
activates the overvoltage comparator, turning off the high-side MOSFET and masking it from turning on until the
output voltage is lower than 107% of the nominal voltage.
A use of the SS/TR (slow start pr tracking) pin is to minimize inrush currents or provide power-supply sequencing
during power up. Couple a small-value capacitor to the pin for slow start. Discharging the SS/TR pin before the
output powers up ensures a repeatable restart after an overtemperature fault, UVLO fault, or disabled condition.
The use of a frequency foldback circuit reduces the switching frequency during start-up and overcurrent fault
conditions to help limit the inductor current.
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