Datasheet

Table Of Contents

TPS54060

SLVS919A –JANUARY 2009–REVISED JULY 2010

www.ti.com

DETAILED DESCRIPTION

Fixed Frequency PWM Control

The TPS54060 uses an adjustable fixed frequency, peak current mode control. The output voltage is compared

through external resistors on the VSENSE pin to an internal voltage reference by an error amplifier which drives

the COMP pin. An internal oscillator initiates the turn on of the high side power switch. The error amplifier output

is compared to the high side power switch current. When the power switch current reaches the level set by the

COMP voltage, the power switch is turned off. The COMP pin voltage will increase and decrease as the output

current increases and decreases. The device implements a current limit by clamping the COMP pin voltage to a

maximum level. The Eco-Mode™ is implemented with a minimum clamp on the COMP pin.

Slope Compensation Output Current

The TPS54060 adds a compensating ramp to the switch current signal. This slope compensation prevents

sub-harmonic oscillations. The available peak inductor current remains constant over the full duty cycle range.

Pulse Skip Eco-Mode

The TPS54060 operates in a pulse skip Eco mode at light load currents to improve efficiency by reducing

switching and gate drive losses. The TPS54060 is designed so that if the output voltage is within regulation and

the peak switch current at the end of any switching cycle is below the pulse skipping current threshold, the

device enters Eco mode. This current threshold is the current level corresponding to a nominal COMP voltage or

500mV.

When in Eco-mode, the COMP pin voltage is clamped at 500mV and the high side MOSFET is inhibited. Further

decreases in load current or in output voltage can not drive the COMP pin below this clamp voltage level.

Since the device is not switching, the output voltage begins to decay. As the voltage control loop compensates

for the falling output voltage, the COMP pin voltage begins to rise. At this time, the high side MOSFET is enabled

and a switching pulse initiates on the next switching cycle. The peak current is set by the COMP pin voltage. The

output voltage re-charges the regulated value (see Figure 25), then the peak switch current starts to decrease,

and eventually falls below the Eco mode threshold at which time the device again enters Eco mode.

For Eco mode operation, the TPS54060 senses peak current, not average or load current, so the load current

where the device enters Eco mode is dependent on the output inductor value. For example, the circuit in

Figure 50 enters Eco mode at about 20 mA of output current. When the load current is low and the output

voltage is within regulation, the device enters a sleep mode and draws only 116mA input quiescent current. 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.

Product Folder Link(s): TPS54060