OUT
ONmin
IN
V
t
=
260 ns
V
IN
OUT
LPFMpeak
ONmin
(V
V
)
I
=
t
L
-
I
= 0.5 x I
OUT_PFM/PWM
LPFMpeak
TPS62230, TPS62231, TPS62232, TPS62233, TPS62234, TPS62235, TPS62236
TPS62237, TPS62238, TPS62239, TPS622310, TPS622311, TPS622312
TPS622313, TPS622314, TPS622315, TPS622316, TPS622317, TPS622318
SLVS941E – APRIL 2009 – REVISED DECEMBER 2010
www.ti.com
DETAILED DESCRIPTION
The TPS6223X synchronous step down converter family includes a unique hysteretic PWM controller scheme
which enables switch frequencies over 3MHz, excellent transient and AC load regulation as well as operation
with cost competitive external components.
The controller topology supports forced PWM Mode as well as Power Save Mode operation. Power Save Mode
operation reduces the quiescent current consumption down to 22mA and ensures high conversion efficiency at
light loads by skipping switch pulses. In forced PWM Mode, the device operates on a quasi fixed frequency,
avoids pulse skipping, and allows filtering of the switch noise by external filter components.
The TPS6223X devices offer fixed output voltage options featuring smallest solution size by using only three
external components.
The internal switch current limit of typical 850mA supports output currents of up to 500mA, depending on the
operating condition.
A significant advantage of TPS6223X compared to other hysteretic PWM controller topologies is its excellent DC
and AC load regulation capability in combination with low output voltage ripple over the entire load range which
makes this part well suited for audio and RF applications.
OPERATION
Once the output voltage falls below the threshold of the error comparator, a switch pulse is initiated, and the high
side switch is turned on. It remains turned on until a minimum on time of tONmin expires and the output voltage
trips the threshold of the error comparator or the inductor current reaches the high side switch current limit. Once
the high side switch turns off, the low side switch rectifier is turned on and the inductor current ramps down until
the high side switch turns on again or the inductor current reaches zero.
In forced PWM Mode operation, negative inductor current is allowed to enable continuous conduction mode even
at no load condition.
POWER SAVE MODE
Connecting the MODE pin to GND enables the automatic PWM and power-save mode operation. The converter
operates in quasi fixed frequency PWM mode at moderate to heavy loads and in the PFM (Pulse Frequency
Modulation) mode during light loads, which maintains high efficiency over a wide load current range. In PFM
Mode, the device starts to skip switch pulses and generates only single pulses with an on time of tONmin. The
PFM Mode frequency depends on the load current and the external inductor and output capacitor values. The
PFM Mode of TPS6223X is optimized for low output voltage ripple if small external components are used. Even
at low output currents, the PFM frequency is above the audible noise spectrum and makes this operation mode
suitable for audio applications.
The on time tONmin can be estimated to:
(1)
Therefore, the peak inductor current in PFM mode is approximately:
(2)
The transition from PFM into PWM mode and vice versa can be estimated to:
(3)
With
tON: High side switch on time [ns]
VIN: Input voltage [V]
VOUT: Output voltage [V]
L : Inductance [mH]
ILPFMpeak : PFM inductor peak current [mA]
IOUT_PFM/PWM : Output current for PFM to PWM mode transition and vice versa [mA]
20
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