MAX684 데이터 시트보기 (PDF) - Maxim Integrated
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MAX684 Datasheet PDF : 12 Pages
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3.3V-Input to Regulated 5V-Output
Charge Pumps
Table 2. Recommended Capacitor Values
for Quiescent Current (Skip Mode)
PART
OUTPUT
(mA)
CIN
(µF)
CX
COUT (µF)
(µF) TANTALUM CERAMIC
VOUT
RIPPLE
(mV)
MAX682 250 2.2 1
47
10
100
MAX683 100 1 0.47 22
4.7
100
ON
OFF
VON
REXT
IN
CIN
2
SHDN
3
IN
1 SKIP
MAX682
MAX683
MAX684
7
CXP
CXN 6
8
OUT
GND
PGND
4
5
CX
OUT
COUT
MAX684 50 0.47 0.22 10
2.2
100
Figure 5. Standard Operating Circuit
Table 3. Recommended Capacitor Values
for Smallest Size (Constant-Frequency
Mode, ISHDN = 22µA, 1MHz)
PART
OUTPUT
(mA)
CIN
(µF)
CX
(µF)
CERAMIC
COUT
(µF)
VOUT
RIPPLE
(mV)
MAX682 250
1 0.47
2.2
80
MAX683 100
0.47 0.22
1
80
MAX684 50
0.22 0.1
0.47
80
3.3VIN
5V/500mA
IN OUT
SKIP
100k
1µF
MAX682
SHDN
CXP
0.47µF
CXN
GND PGND
IN
OUT
SKIP
100k
MAX682
1µF
SHDN
CXP
0.47µF
CXN
GND PGND
4.7µF
Table 4. Recommended Capacitor
Manufacturers
VALUE DESCRIPTION MANUFACTURER
PHONE
NUMBER
47µF to
10µF
47µF to
10µF
0.1µF to
2.2µF
595D-series
tantalum
surface mount
TPS-series
surface mount
Ceramic
surface mount
Sprague
AVX
TDK
(603) 224-1961
(803) 946-0690
(847) 390-4373
In addition, the following two equations approximate
output ripple for each mode. In skip mode, output rip-
ple is dominated by ESR, and is approximately:
VRIPPLE(SKIP) ≅ (2VIN - VOUT)ESRCOUT / RTX
Figure 6. Paralleling Two MAX682s
where ESRCOUT is the ESR of the output filter capaci-
tance, and RTX is the open-loop output transfer resist-
ance of the IC. RTX is typically 0.8Ω for the MAX682,
1.6Ω for the MAX683, and 3Ω for the MAX684. In con-
stant-frequency mode, output ripple is dominated by
COUT and is approximately:
VRIPPLE(const-freq) ≅ IOUT / (2 x fOSC x COUT)
All capacitors must maintain a low (<100mΩ) equiva-
lent series resistance (ESR). Table 4 lists the manufac-
turers of recommended capacitors. Surface-mount
tantalum capacitors will work well for most applications.
Ceramic capacitors will provide the lowest ripple due to
their typically lower ESR.
If the source impedance or inductance of the input sup-
ply is large, additional input bypassing (2.2µF to 22µF)
may be needed. This additional capacitance need not
be a low-ESR type.
8 _______________________________________________________________________________________
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