Rainbow Electronics MAX619 - Manual (Page 6)

MAX619
Regulated 5V Charge-Pump
DC-DC Converter
6 ________________________________________________________________________________________
Table 1. Capacitor Suppliers
* Note: (SM) denotes surface-mount component, (TH) denotes through-hole component.
__________Applications Information
Capacitor Selection
Charge-Pump Capacitors C1 and C2
The values of charge-pump capacitors C1 and C2 are
critical to ensure adequate output current and avoid
excessive peak currents. Use values in the range of
0.22
µ F to 1.0 µ F. Larger capacitors (up to 50 µ F) can
be used, but larger capacitors will increase output rip-
ple. Ceramic or tantalum capacitors are recommend-
ed.
Input and Output Capacitors, C3 and C4
The type of input bypass capacitor (C3) and output fil-
ter capacitor (C4) used is not critical, but it does affect
performance. Tantalums, ceramics, or aluminum elec-
trolytics are suggested. For smallest size, use Sprague
595D106X0010A2 surface-mount capacitors, which
measure 3.7mm x 1.8mm (0.146in x 0.072in). For low-
est ripple, use large, low effective-series-resistance
(ESR) ceramic or tantalum capacitors. For lowest cost,
use aluminum electrolytic or tantalum capacitors.
Figure 2 shows the component values for proper oper-
ation using minimal board space. The input bypass
capacitor (C3) and output filter capacitor (C4) should
both be at least 10
µ F when using aluminum electrolyt-
ics or Sprague’s miniature 595D series of tantalum chip
capacitors.
When using ceramic capacitors, the values of C3 and
C4 can be reduced to 2
µ F and 1 µ F, respectively. If the
input supply source impedance is very low, C3 may not
be necessary.
Many capacitors exhibit 40% to 50% variation over
temperature. Compensate for capacitor temperature
coefficient by selecting a larger nominal value to
ensure proper operation over temperature. Table 1 lists
capacitor suppliers.
MAX619
C4
10µF
IN
C1+
C1–
OUT
SHDN
C2+
C2–
GND
7
4
5
6
2
1
8
3
C3
10µF
2
CELLS
C1
0.22µF C2
0.22µF
5V ±4%
@ 20mA
Figure 2. Two-Cell to 5V Application Circuit
10 µ F tantalum (SM) 595D106X0010A2
(603) 224-1430
(207) 324-7223 (603) 224-1961
(207) 327-4140 Sprague Electric
(smallest size)
0.1
µ
F ceramic (TH) RPE121Z5U104M50V
(814) 238-0490 (814) 237-1431 Murata Erie
1.0 µ F ceramic (TH) RPI123Z5U105M50V
0.22 µ F ceramic (SM) GRM42-6Z5U22M50
0.1
µ
F ceramic (SM) GRM42-6Z5U10M50
CAPACITOR TYPE* CAPACITOR FAX NUMBER PHONE NUMBER SUPPLIER