ADP3604

REV. 0

–5–

TEMPERATURE –

°C

10

1.0

0.01

–50

100

050

0.1

ALUMINUM

CERAMIC

ORGANIC SEMIC

TANTALUM

ALUMINUM

CERAMIC

ORGANIC SEMIC

TANTALUM

Figure 16. ESR vs. Temperature

Table I. Alternative Capacitor Technologies

High

Type

Life

Freq

Temp

Size

Cost

Aluminum

Fair

Fair

Fair

Small

Low

Electrolytic

Capacitor

Multilayer

Long

Good

Poor

Fair

High

Ceramic

Capacitor

Solid

Above

Avg

Avg

Avg

Avg

Tantalum

Avg

Capacitor

OS-CON

Above

Good

Good

Good

Avg

Capacitor

Avg

The following is a partial list of manufacturers providing low

ESR capacitors.

Table II. Recommended Capacitor Manufacturers

Manufacturer

Capacitor

Capacitor Type

Sprague

672D, 673D,

Aluminum Electrolytic

674D, 678D

Sprague

675D, 173D,

Tantalum

199D

Nichicon

PF & PL

Aluminum Electrolytic

Mallory

TDC & TDL

Tantalum

TOKIN

MLCC

Multilayer Ceramic

muRata

GRM

Multilayer Ceramic

EXTERNAL OUTPUT FILTERING

In applications requiring very low power supply ripple and

noise, the circuit in Figure 18 provides low noise and ripple of

less than 2% of the output voltage over the full load current and

temperature.

Since output current is supplied solely by the output capacitor

C3 during one-half of the charge-pump cycle, peak-to-peak

output ripple voltage is calculated by using the following

formula:

+ I

In Figure 15, output ripple voltage vs. capacitance and various

ESR are shown.

CAPACITANCE – µF

120

0

0

180

20

40

60

80

100

120

140

160

100

80

60

40

20

ESR

C

140mA

V

OUT

ADP3604

150m

Ω

100m

Ω

50m

Ω

Figure 15. Output Ripple Voltage (mV) vs. Capacitance

and ESR

Note that as the capacitor value increases beyond the point

where the dominant contribution to the output ripple is due to

added capacitance.

A low ESR capacitor has much greater impact on performance

for C2 than C3 since current through C2 is twice the C3 cur-

as well as during discharges. Therefore, the voltage drop due to

C2 is about 4 times C2’s ESR times the load current. The volt-

age drop generated by C2’s ESR combined with the voltage

drop due to the output source resistance, determines the maxi-

ripple.

When selecting the capacitors, keep in mind that not all manu-

facturers guarantee capacitor ESR in the range required by the

circuit. In general, the capacitor’s ESR is inversely proportional

to its physical size, so larger capacitance values and higher volt-

age ratings tend to reduce ESR.

ESR is also a function of the operating frequency. When select-

ing a capacitor, make sure its value is rated at the circuit’s oper-

ating frequency. The other factor affecting the capacitor’s

performance is temperature. If the circuit has to operate at tem-

peratures significantly different than 25

°C, the capacitance and

ESR values must be carefully selected to adequately compen-

sate for the change. Various capacitor technologies offer im-

proved performance over temperature, for example, certain

tantalum capacitors provide good low-temperature ESR but at

a higher cost.

Figure 16 demonstrates the effect temperature has on various

capacitors. ADP3604’s high internal oscillator frequency per-

mits the usage of smaller capacitance for both the pump and

the output capacitors.