Datasheet

 
 
SLVS391B − OCTOBER 2001 − REVISED FEBRUARY 2002
15
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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
86
C1F− C1F+
C2F
1 µF
34
C2F− C2F+
7
OUT
10
FB
+
C
o
10 µF
C
(P)
max 150 mA
2
PG
R
5
VIN
1
EN
GND
9
OFF/ON
C
i
2.2 µF
2.5 V to 6.5 V
INPUT
TPS60503
L
(P)
V
P(out)
Figure 28. LC-Post Filter
Table 3. Measurement Results on Different C
(fly)
, C
(P)
, L
(P)
Combinations; BW = 500 MHz
V
I
[V]
I
O
[mA]
C
I
[µF]
C
(XF)
[µF]
C
O
[µF]
L
(P)
[µH]
C
(P)
[µF]
V
O
[V]
TYPICAL
V
P(Out)
TYPICAL
V
O(RMS)
I
[V]
O
[mA]
CERAMIC CERAMIC CERAMIC
(P)
[
µ
H]
CERAMIC
O
[V]
V
P(Out)
V
PP
[mV]
V
O(RMS)
[mV]
5 50 2.2 0.22 4.7 — 0.1 (X7R) 3.3 50 8
5 50 2.2 0.22 4.7 — 0.1 (X7R) 1.5 30 9
5 150 4.7 1 10 — 0.1 (X7R) 1.5 50 6
5 250 4.7 1 2 x 10 — 0.1 (X7R) 1.5 45 8
5 100 4.7 1 10 0.1 0.1 (X7R) 1.5 20 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.