Rainbow Electronics MAX8614B - Manual (Page 12)

MAX8614A/MAX8614B
Dual-Output (+ and -) DC-DC
Converters for CCD
12 ______________________________________________________________________________________
For stability, the inverter output filter capacitor, C2,
should satisfy the following:
C2 > (6L V REF I INVMAX ) /
(R CS D- (V REF - V INV ) V INV )
where R CS = 0.0175 (MAX8614B), and 0.040
(MAX8614A). D- is 1 minus the inverter switch duty cycle
and is:
D- = V CC / V INV
Table 2 lists representative low-ESR capacitor suppliers.
Input Bypass Capacitor
Although the output current of many MAX8614A/
MAX8614B applications may be relatively small, the
input must be designed to withstand current transients
equal to the inductor current limit. The input bypass
capacitor reduces the peak currents drawn from the
voltage source, and reduces noise caused by the
MAX8614A/MAX8614B switching action. The input
source impedance determines the size of the capacitor
required at the input. As with the output filter capacitor,
a low-ESR capacitor is recommended. A 4.7µF, low-
ESR capacitor is adequate for most applications,
although smaller bypass capacitors may also be
acceptable with low-impedance sources or if the source
supply is already well filtered. Bypass AV
CC separately
from V
CC
with a 0.1µF ceramic capacitor placed as
close as possible to the AV
CC
and GND pins.
PC Board Layout and Routing
Proper PC board layout is essential due to high-current
levels and fast-switching waveforms that radiate noise.
Breadboards or protoboards should never be used
when prototyping switching regulators.
Table 1. Inductor Selection Guide
OUTPUT VOLTAGES
AND LOAD CURRENT
INDUCTOR L ( µH) DCR (m Ω) I SAT (A) SIZE (mm)
TOKO
DB3018C, 1069AS-2R0
2.0 72 1.4 3 x 3 x 1.8
TOKO
DB3018C, 1069AS-4R3
4.3 126 0.97 3 x 3 x 1.8
TOKO
S1024AS-4R3M
4.3 47 1.2 4 x 4 x 1.7
Sumida
CDRH2D14-4R7
4.7 170 1 3.2 x 3.2 x 1.55
15V, 50mA
-7.5V, 100mA
TOKO
S1024AS-100M
10 100 0.8 4 x 4 x 1.7
Sumida
CDRH2D11-100
10 400 0.35 3.2 x 3.2 x 1.2
Sumida
CDRH2D14-100
10 295 0.46 3.2 x 3.2 x 1.55
15V, 20mA
-7.5V, 40mA
Murata
LQH32CN100K33
10 300 0.45 3.2 x 2.5 x 2
Table 2. Component Suppliers
SUPPLIER PHONE WEBSITE
INDUCTORS
Murata 770-436-1300 www.murata.com
Sumida 847-545-600 www.sumida.com
TOKO 847-297-0070 www.tokoam.com
DIODES
Central
Semiconductor
(CMHSH5-2L)
631-435-1110 www.centralsemi.com
Motorola
(MBR0540L)
602-303-5454 www.motorola.com
CAPACITORS
Taiyo Yuden 408-573-4150 www.t-yuden.com
TDK 888-835-6646 www.TDK.com