Datasheet

PFM Mode at Light Load
Comparator High
Comparator Low
Comparator Low 2
PWM Mode at Medium to Full Load
1.6%
0.8%
V
O
DYNAMIC VOLTAGE POSITIONING
DIGITAL SELF-CALIBRATION
SOFT START
TPS62220 , , TPS62221 , , TPS62222
TPS62223 , TPS62224 , TPS62225
TPS62227 , TPS62228 , TPS62229
www.ti.com ....................................................................................................................................... SLVS491E – SEPTEMBER 2003 – REVISED FEBRUARY 2009
Figure 14. 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.
As described in the power-save mode operation sections and as detailed in Figure 14 , 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 by turning on
the N-channel rectifier switch.
In addition to the control circuit as shown in the block diagram, the TPS6222x series uses an internal digital
self-calibration of the output voltage to minimize DC load and line regulation. This method of self-calibration
allows simple internal loop compensation without the use of external components. The device monitors the
output voltage and as soon as the output voltage drops below typically 1.6% or exceeds typically 1.6% of Vout
the duty cycle will be adjusted in digital steps. As a result, the output voltage changes in digital steps either up or
down where one step is typically 1% of Vout. This results in virtually zero line and load regulation and keeps the
output voltage tolerance within ± 3% overload and line variations.
The TPS6222x 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 TPS6222x. The soft start is implemented as a digital circuit increasing the switch current in steps
of typically 83 mA, 167 mA, 335 mA and then the typical switch current limit of 670 mA. Therefore, the start-up
time mainly depends on the output capacitor and load current.
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Product Folder Link(s): TPS62220 TPS62221 TPS62222 TPS62223 TPS62224 TPS62225 TPS62227 TPS62228
TPS62229