TPS62200, TPS62201

TPS62202, TPS62203

TPS62204, TPS62205

SLVS417B – MARCH 2002 – REVISED OCTOBER 2002

5

www.ti.com

power save mode operation (continued)

PFM Mode at Light Load

Comparator High

Comparator Low

Comparator Low 2

PWM Mode at Medium to Full Load

1.6%

0.8%

VO

Figure 2. Power Save Mode Thresholds and Dynamic Voltage Positioning

The converter enters the fixed frequency PWM mode again as soon as the output voltage falls below the comp

low 2 threshold.

dynamic voltage positioning

As described in the power save mode operation sections and as detailed in Figure 2, the output voltage is

typically 0.8% above the nominal output voltage at light load currents, as the device is in power save mode. This

gives additional headroom for the voltage drop during a load transient from light load to full load. During a load

transient from full load to light load, the voltage overshoot is also minimized due to active regulation turning on

the N-channel rectifier switch.

soft start

The TPS6220x has an internal soft start circuit that limits the inrush current during start-up. This prevents

possible voltage drops of the input voltage in case a battery or a high impedance power source is connected

to the input of the TPS6220x.

The soft start is implemented as a digital circuit increasing the switch current in steps of typically 60 mA,

120 mA, 240 mA and then the typical switch current limit of 480 mA. Therefore the start-up time mainly depends

on the output capacitor and load current. Typical start-up time with 10

µF output capacitor and 200 mA load

current is 800

µs.

low dropout operation 100% duty cycle

The TPS6220x offers a low input to output voltage difference, while still maintaining operation with the 100%

duty cycle mode. In this mode, the P-channel switch is constantly turned on. This is particularly useful in battery

powered applications to achieve longest operation time by taking full advantage of the whole battery voltage

range. The minimum input voltage to maintain regulation, depending on the load current and output voltage,

can be calculated as

Vin

r

ds