Datasheet

( )
2
OUT
RMP[2-0]
ΔV
mV 1
= 32
Δt μs
2
350 20ns ns´ +
OUT
ON
IN
V
t =
V
( )
´ -
ON
L,PFM,peak IN OUT
t
I = V V
L
TPS62360, TPS62361B
TPS62362, TPS62363
SLVSAU9C –MAY 2011–REVISED NOVEMBER 2012 www.ti.com
The TPS6236x is optimized for low output voltage ripple. Therefore, the peak inductor current in PFM mode is
kept small and can be calculated as follows:
(2)
And:
(3)
With:
V
IN
= Input Voltage
V
OUT
= Output Voltage
t
ON
= On-time of the High Side FET, from Equation 3
L = Inductor value
The TPS6236x offers a forced PWM mode as well. In this mode, the converter is forced in PWM mode even at
light load currents. This comes with the benefit that the converter is operating with lower output voltage ripple.
Compared to the PFM mode, the efficiency is lower during light load currents.
According to the output voltage, the Power Save Mode / forced PWM Mode can be programmed individually for
each preset via I
2
C by setting the MODE0 – MODE3 bit D7. Table 2 shows the factory presets after enabling the
I
2
C. For additional flexibility, the Power Save Mode can be changed at a preset that is currently active.
RAMP RATE CONTROLLING
If the output voltage is changed, the TPS6236x can actively control the voltage ramp rate during the transition.
An internal oscillator is embedded for high timing precision.
Figure 38 and Figure 39 show the operation principle. If the output voltage changes, the device will change the
output voltage through discrete steps with a programmable ramp rate resulting in a corresponding transition time.
The ramp up/down slope can be programmed via I
2
C interface (see Table 5).
Table 5. Ramp Rates
RAMP RATE
RMP [2:0]
[mV/µs] [µs/10mV]
000 32 0.3125
001 16 0.625
010 8 1.25
011 4 2.5
100 2 5
101 1 10
110 0.5 20
111 0.25 40
For a transition of the output voltage from V
OUT,A
to V
OUT,B
and vice versa, the resulting ramp up/down slope can
be calculated as
(4)
If the device is operating in forced PWM Mode, the device actively controls both the ramp up and down slope.
If Power Save Mode is activated, the ramp up phase follows the programmed slope.
To force the output voltage to follow the ramp down slope in Power Save Mode, the RAMP_PFM bit needs to be
set. This will force the converter to follow the ramp down slope during PFM operation as well.
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