TPS60500, TPS60501
TPS60502, TPS60503
SLVS391B − OCTOBER 2001 − REVISED FEBRUARY 2002
APPLICATION INFORMATION
LC-post filter
If the output voltage ripple of the stepdown charge pump is to high, an LC post filter can be used.
C1F
1
µF
C2F
1
µF
8
6
3
4
7
+ C
o
10
µF
L(P) max 150 mA
VP(out)
C1F− C1F+ C2F− C2F+
INPUT
2.5 V to 6.5 V
Ci
2.2
µF
OUT
5
VIN
TPS60503
FB
1
EN
PG
GND
9
C(P)
10
R
2
OFF/ON
Figure 28. LC-Post Filter
Table 3. Measurement Results on Different C
(fly)
, C
(P)
, L
(P)
Combinations; BW = 500 MHz
VI
[V]
5
5
5
5
5
IO
[mA]
50
50
150
250
100
CI
[µF]
CERAMIC
2.2
2.2
4.7
4.7
4.7
C(XF)
[µF]
CERAMIC
0.22
0.22
1
1
1
CO
[µF]
CERAMIC
4.7
4.7
10
2 x 10
10
L(P)
[µH]
—
—
—
—
0.1
C(P)
[µF]
CERAMIC
0.1 (X7R)
0.1 (X7R)
0.1 (X7R)
0.1 (X7R)
0.1 (X7R)
V
O
[V]
3.3
1.5
1.5
1.5
1.5
TYPICAL
VP(Out)
VPP[mV]
50
30
50
45
20
TYPICAL
VO(RMS)
[mV]
8
9
6
8
4
power supply with dynamic voltage scaling
Dynamic voltage scaling of the core can be used to reduce power consumption of a digital signal processor
(DSP). During the periods, in which the maximum DSP performance is not required, the core voltage can be
reduced when the DSP operates at a lower clock-rate. This idea is called runtime power control (RPC) and is
supported by modern DSPs. RPC extends battery-life time in handheld applications, like MP3 players, digital
cameras, PDA.
The supply of DSPs is separated into I/O interface and core supply. Interface is mostly powered by a 3.3-V
system supply, whereas core supply achieves voltages far below 1.5 V. The TPS60500 is powered by the 3.3-V
system supply. The DSP itself selects the applied core voltage.
The core voltage is switched between 1.5 V and 1.1 V by changing the feedback resistor network. A MOSFET
modifies the voltage divider at the feedback (FB) pin by switching a resistor. In this application, a general
purpose MOSFET BSS138 is used with a V
GS(th)
of 1.6 V. A DSP 3.3-V I/O port drives the gate. The feedback
resistor network consists of R2, R3 and R4. C
(ff)
is the fast forward capacitor for improved line regulation.
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