Regulated 5V Charge-Pump

DC-DC Converter

6

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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

µF to 1.0µF. Larger capacitors (up to 50µF) 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

µF 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

µF and 1µF, 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

µF tantalum (SM)

595D106X0010A2

(603) 224-1430

(207) 324-7223

(603) 224-1961

(207) 327-4140

Sprague Electric

(smallest size)

0.1

µF ceramic (TH)

RPE121Z5U104M50V

(814) 238-0490

(814) 237-1431

Murata Erie

1.0

µF ceramic (TH)

RPI123Z5U105M50V

0.22

µF ceramic (SM)

GRM42-6Z5U22M50

0.1

µF ceramic (SM)

GRM42-6Z5U10M50

CAPACITOR TYPE*

CAPACITOR

FAX NUMBER

PHONE NUMBER

SUPPLIER