Datasheet

TPS62040
TPS62042, TPS62043
TPS62044, TPS62046
SLVS463B − JUNE 2003 − REVISED OCTOBER 2005
www.ti.com
11
1.6%
0.8%
V
O
Comp High
Comp Low
Comp Low 2
PWM Mode at Medium to Full Load
PFM Mode at Light Load
Figure 14. Power Save Mode Thresholds and Dynamic Voltage Positioning
The converter enters the fixed frequency PWM mode 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 before and as detailed in Figure 14 the output voltage is
typically 0.8% (i.e., 1% on average) 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.
In the other direction during a load transient from full load to light load the voltage overshoot is also minimized by
turning on the N-Channel rectifier switch to pull the output voltage actively down.
MODE (AUTOMATIC PWM/PFM OPERATION AND FORCED PWM OPERATION)
Connecting the MODE 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,
maintaining high efficiency over a wide load current range.
Pulling the MODE pin high forces the converter to operate constantly in the PWM mode even at light load currents.
The advantage is the converter operates with a fixed switching 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 (see Figure 1 to Figure 3). 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
TPS6204x to the specific system requirements.
100% DUTY CYCLE LOW DROPOUT OPERATION
The TPS6204x offers a low input to output voltage difference while still maintaining regulation with the use of 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.
i.e. The minimum input voltage to maintain regulation depends on the load current and output voltage and can be
calculated as:
V
I
min + V
O
max ) I
O
max
ǒ
r
DS(on)
max ) R
L
Ǔ
with:
I
O(max)
= maximum output current plus inductor ripple current
r
DS(on)
max= maximum P-channel switch t
DS(on)
.
R
L
= DC resistance of the inductor
V
O
max = nominal output voltage plus maximum output voltage tolerance
(2)