SC600
POWER MANAGEMENT
Applications Information (Cont.)
Comparison with Other Regulation Methods
In many instances, a charge pump regulator is the best
choice for portable power applications. These regulators
offer many advantages over switch mode regulators. A
smaller bill of materials, less layout area, lower compo-
nent height, less noise, no EMF, and less overall circuit
cost are typical reasons to use this type of regulation. In
some cases the efficiency of a charge pump regulator ex-
ceeds the efficiency of a switch mode regulator.
Inductors are often the largest and most expensive dis-
crete component in a design. Because there are no in-
ductors used in the SC600, cost, noise, layout area, as
well as the the EMF associated with the inductor, are
eliminated.
The SC600’s
fi
xed frequency harmonics are an advantage
in portable communications equipment, such as cellular
telephones. The SC600 has distinct frequencies of op-
eration, so the harmonics are predictable. The harmonics
are not
fi
xed in a switch mode regulator.
Table 1 -Frequency Selection Logic
Sw itching Frequency
32kHz
8kHz
262kHz
650kHz
C X8
0
0
1
1
CD4
0
1
0
1
Ripple Performance
Examples of the output ripple, charge pump frequency
and capacitor size are listed in Table 2.
Switch mode regulators have harmonics which vary due to
the pulse width modulation used to regulate the output.
Varying harmonics can make it difficult to ensure accept-
able noise performance over the entire operating range.
Many switch mode regulators have increased voltage rip-
ple on the output during pulse skipping mode due to large
periods of time when no current is supplied to the output.
The SC600 supplies current to the output continuously,
so the voltage ripple is less than a switch mode regula-
tor, even with greatly reduced output capacitance. The
SC600 delivers a continuous current to the output during
1x, 1.5x and 2x modes. Most of the battery life requires
1.5x mode.
Frequency Selection
CX8 and CD4 are frequency select inputs; input from a µP
or other device may be used to change the charge pump
frequency at any time (as shown in Table 1). The opti-
mal frequency will depend upon the capacitor values, the
load current, and the acceptable amount of output ripple.
Lower frequencies will be more efficient, while higher fre-
quencies will support higher output currents with lower
ripple.
Table 2 -Ripple Performance
Part No.
SC600A 5.0V
Freq. [kHz ]
8
32
262
650
650
I
OUT
[mA]
5
20
60
60
60
Output Ripple [mVp-p]
1.5x mode
65
150
25
10
20
Ouput Ripple [mVp-p]
2x mode
15
25
20
15
25
C
OUT
[
μ
F]
1
1
1
1
0.33
C
BUCKET
[
μ
F]
1
1
1
1
1
©
2006 Semtech Corp.
10
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