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