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| SP6650 Datasheet, PDF (13/17 Pages) Sipex Corporation – High Efficiency 600mA Synchronous Buck Regulator Ideal for portable designs powered with Li Ion battery | |||
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ADDITIONAL APPLICATION CIRCUITS
Vin 2.7-6.5 VDC
RB
100k
RVIN
10.0
CVIN
1.0µF
CIN
47µF
1 PVIN
®
LX 10
2 VIN
PGND 9
3
SP6650
BLON U1 GND
8
4 ILIM
VOUT 7
5 SHDN
FB 6
L1 22µH
Rf
4.99k
Cf
33nF
R2
160k
R3
100k
3.3V/600mA
COUT
47µF
Figure 16. Additional Application Circuit with Low Output Ripple
The additional Rf/Cf network used in Figure 16
generates an artificial ramp from the LX pin
voltage and superimposes it to the feedback pin.
As a result, the internal loop comparator doesnât
have to rely on output ripple to run PFM. Now
low ESR output capacitors, such as ceramic
capacitors, can be used, and the output ripple can
be reduced by two to three times. For the best
result, size the Cf and Rf values so the network
would introduce 10 to 30mV ripples to the FB
pin. Oversized ripple would compromise the
load regulation and also cause oscillation during
load transient. Load transient response and out-
put ripples from Figure 16 circuit are shown in
Figure 17 and Figure 18, respectively. The added
ripple voltage can be calculated from
âV
=
KON
RfCf
Figure 17. VOUT transient response from 50mA to
500mA load step. CH1- VOUT, CH4 - ILOAD
Figure 18. Output ripple CH1-output ripple. VIN = 5,
VOUT = 3.3V, ILOAD = 600mA
Date: 5/25/04
SP6650 High Efficiency 600mA Synchronous Buck Regulator
13
© Copyright 2004 Sipex Corporation
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