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POWER-SAVE MODE

I

PFM PWM

+

V

O

V

I

V

I

* V

O

2

L

fsw

(1)

3-MHz Operation

Comp Low Thershold

MODE SELECTION AND FREQUENCY SYNCHRONIZATION

SOFT START

TPS62300, TPS62301, TPS62302

TPS62303, TPS62304, TPS62305,

TPS62311, TPS62313, TPS62315, TPS62320, TPS62321

SLVS528E – JULY 2004 – REVISED NOVEMBER 2007

With decreasing load current, the device automatically switches into pulse skipping operation in which the power

stage operates intermittently based on load demand. By running cycles periodically, the switching losses are

minimized, and the device runs with a minimum quiescent current and maintaining high efficiency.

In power-save mode, the converter only operates when the output voltage trips below a set threshold voltage

output voltage exceeds the nominal output voltage. As a consequence, the average output voltage is slightly

lower than its nominal value in the power-save mode operation.

The output current at which the PFM/PWM transition occurs is approximated by Equation 1:

• I

• f

• L : inductor value

Figure 31. Power-Save Mode Threshold

The MODE/SYNC pin is a multipurpose pin which allows mode selection and frequency synchronization.

Connecting this pin to GND enables the automatic PWM and power-save mode operation. The converter

operates in fixed frequency PWM mode at moderate to heavy loads and in the PFM mode during light loads,

which maintains high efficiency over a wide load current range.

Pulling the MODE/SYNC pin high forces the converter to operate in the PWM mode even at light load currents.

The advantage is that the converter operates with a fixed frequency that allows simple filtering of the switching

frequency for noise-sensitive applications. In this mode, the efficiency is lower compared to the power-save

mode during light loads. For additional flexibility, it is possible to switch from power-save mode to forced PWM

mode during operation. This allows efficient power management by adjusting the operation of the converter to

the specific system requirements.

The TPS6230x, TPS6231x, and TPS6232x can also be synchronized to an external 3-MHz clock signal by the

MODE/SYNC pin. During synchronization, the mode is set to fixed-frequency operation and the P-channel

MOSFET turnon is synchronized to the falling edge of the external clock. This creates the ability for multiple

converters to be connected together in a master-slave configuration for frequency matching of the converters

(see the application section for more details, Figure 37).

The TPS6230x, TPS6231x, and TPS6232x have an internal soft-start circuit that limits the inrush current during

start-up. This prevents possible input voltage drops when a battery or a high-impedance power source is

connected to the input of the converter. The soft start is implemented as a digital circuit increasing the switch

current in steps of typically 195 mA, 390 mA, 585 mA, and the typical switch current limit of 780 mA.

The current limit transitions to the next step every 256 clocks (

≈88µs). To be able to switch from 390 mA to 585

operate at the 390-mA current limit. This mechanism is used to limit the output current under short-circuit

conditions. Therefore, the start-up time mainly depends on the output capacitor and load current.

16

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Product Folder Link(s): TPS62300, TPS62301, TPS62302 TPS62303, TPS62304, TPS62305, TPS62311, TPS62313,

TPS62315, TPS62320, TPS62321