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t − Time − 400 ms/div

t − Time − 50 ms/div

DETAILED DESCRIPTION

OPERATION

TPS62300, TPS62301, TPS62302

TPS62303, TPS62305, TPS62311

TPS62313, TPS62320, TPS62321

SLVS528B – JULY 2004 – REVISED JUNE 2005

TYPICAL CHARACTERISTICS (continued)

START-UP

POWER DOWN (TPS62321)

Figure 29.

Figure 30.

The TPS6230x, TPS6231x, and TPS6232x are synchronous step-down converters typically operating with a

3-MHz fixed frequency pulse width modulation (PWM) at moderate to heavy load currents. At light load currents,

the converter operates in power-save mode with pulse frequency modulation (PFM). The operating frequency is

set to 3 MHz and can be synchronized on-the-fly to an external oscillator.

During PWM operation, the converter uses a unique fast response, voltage mode, controller scheme with input

voltage feed-forward. This achieves best-in-class load and line response and allows the use of tiny inductors and

small ceramic input and output capacitors. At the beginning of each switching cycle, the P-channel MOSFET

switch is turned on and the inductor current ramps up until the comparator trips and the control logic turns off the

switch.

The device integrates two current limits, one in the P-channel MOSFET and another one in the N-channel

MOSFET. When the current in the P-channel MOSFET reaches its current limit, the P-channel MOSFET is

turned off and the N-channel MOSFET is turned on. When the current in the N-channel MOSFET is above the

N-MOS current limit threshold, the N-channel MOSFET remains on until the current drops below its current limit.

The current limit in the N-channel MOSFET is important for small duty-cycle operation when the current in the

inductor does not decrease because of the P-channel MOSFET current limit delay, or because of start-up

conditions where the output voltage is low.

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