Datasheet

VOUT

(ac)

TPS54160

TPS54160A

SLVSB56C –MAY 2012–REVISED FEBRUARY 2014

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Feature Description (continued)

quiescent current. While the device is in sleep mode the output power is delivered by the output capacitor. As the

load current decreases, the time the output capacitor supplies the load current increases and the switching

frequency decreases reducing gate drive and switching losses. As the output voltage drops, the TPS54160A

wakes up from the sleep mode and the power switch turns on to recharge the output capacitor, see Figure 26.

The internal PLL remains operating when in sleep mode. When operating at light load currents in the pulse skip

mode the switching transitions occur synchronously with the external clock signal.

Figure 26. Pulse Skip Mode Operation

8.3.4 Bootstrap Voltage (BOOT)

The TPS54160A has an integrated boot regulator and requires a small ceramic capacitor between the BOOT and

PH pin to provide the gate drive voltage for the high side MOSFET. The value of the ceramic capacitor should be

0.1 μF. A ceramic capacitor with an X7R or X5R grade dielectric is recommended because of the stable

characteristics over temperature and voltage. To improve drop out, the TPS54160A is designed to operate at

100% duty cycle as long as the BOOT to PH pin voltage is greater than 2.1 V. When the voltage from BOOT to

PH drops below 2.1 V, the high side MOSFET is turned off using an UVLO circuit allowing for the low side diode

to conduct which allows refreshing of the BOOT capacitor. Since the supply current sourced from the BOOT

capacitor is low, the high side MOSFET can remain on for more switching cycles than it refreshes, thus, the

effective duty cycle limitation that is attributed to the boot regulator system is high.

8.3.5 Low Dropout Operation

The duty cycle during dropout of the regulator will be mainly determined by the voltage drops across the power

MOSFET, inductor, low side diode and printed circuit board resistance. During operating conditions in which the

input voltage drops, the high side MOSFET can remain on for 100% of the duty cycle to maintain output

regulation or until the BOOT to PH voltage falls below 2.1 V.

Once the high side is off, the low side diode will conduct and the BOOT capacitor will be recharged. During this

boot capacitor recharge time, the inductor current will ramp down until the high side MOSFET turns on. The

recharge time is longer than the typical high side off time of previous switching cycles, and thus, the inductor

current ripple is larger resulting in more ripple voltage on the output. The recharge time is a function of the input

voltage, boot capacitor value, and the impedance of the internal boot recharge diode.

Attention needs to be taken in maximum duty cycle applications which experience extended time periods without

a load current. When the voltage across the BOOT capacitors falls below the 2.1 V threshold in applications that

have a difference in the input voltage and output voltage that is less than 3V, the high side MOSFET will be

turned off but there is not enough current in the inductor to pull the PH pin down to recharge the boot capacitor.

The regulator will not switch because the boot capacitor is less than 2.1V and the output capacitor will decay until

the difference in the input voltage and output voltage is 2.1 V. At this time the boot under voltage lockout is

exceeded and the device will switch until the desired output voltage is reached.

Product Folder Links: TPS54160 TPS54160A