SP6644 Datasheet, PDF (12/15 Pages) Sipex Corporation – Single/Dual Alkaline Cell, High Efficiency Step-Up DC-DC Converter

noisy traces, such as from the LX pin, should be
kept away from the voltage-feedback network
and separated from it using grounded copper to
minimize EMI.
Capacitor equivalent series resistance is a major
contributor to output ripple, usually greater than
60%. Low ESR capacitors are recommended.
Ceramic capacitors have the lowest ESR.
Low-ESR tantalum capacitors may be a more
acceptable solution having both a low ESR and
lower cost than ceramic capacitors. Designers
should select input and output capacitors with a
rating exceeding the peak inductor current. Do
not allow tantalum capacitors to exceed their
ripple-current ratings. A 22µF, 6V, low-ESR,
surface-mount tantalum output filter capacitor
typically provides 60mV output ripple when
stepping up from 1.3V to 3.3V at 20mA.
An input filter capacitor can reduce peak
currents drawn from the battery and improve
efficiency. Low-ESR aluminum electrolytic
capacitors are acceptable in some applications
but standard aluminum electrolytic capacitors
are not recommended.
Designers should add LC pi filters, linear
post-regulators, or shielding in applications
necessary to address excessive noise, voltage
ripple, or EMI concerns. The LC pi filter's cutoff
frequency should be at least a decade or two
below the DC-DC converters's switching
frequency for the specified load and input voltage.
A small SOT23-5pin 200mA Low Drop Out
linear regulator can be used at the SP6644/6645
output to reduce output noise and ripple. The
schematic in figure 29 illustrates this circuit with
the SP6644 3.3V output followed by the Sipex
SP6201 3.0V output Low Drop Out linear regu-
lator. Compare in Figure 21 the SP6644 ripple of
40-50mVpp with the SP6201 ripple of about
3mVpp and you can see the amount of noise
reduction obtained. Additional performance
characteristics for the SP6644/6201 combina-
tion can be seen in figures 17 to 20.
Inductance
(uH)
22
47
100
Manufacturer/Part No.
Sumida CD43-220
Sumida CDRH5D18-220
Coilcraft DO1608C-223
Sumida CD43-470
Coilcraft DO1608C-473
Sumida CD54-101
Coilcraft DO1608C-104
Table 1. Surface-Mount Inductor Information
Inductor Specification
Resistance
(ohms)
0.38 (max)
0.28 (max)
0.32 (typ)
0.84 (max)
0.56 (typ)
0.7 (max)
1.1(typ)
Isat
(mA)
680
760
700
440
500
520
310
Rev:B Date 4/13/04
SP6644/6645 High Efficiency Boost Regulator
12
© Copyright 2004 Sipex Corporation