REV. A

ADP3610

–7–

APPLICATION INFORMATION

Capacitor Selection

The ADP3610’s high internal oscillator frequency permits the

use of small capacitors for both the pump and the output ca-

pacitors. For a given load current, factors affecting the output

voltage performance are:

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. Since the ESR is also a function

of the operating frequency, when selecting a capacitor, make

sure its value is rated at the circuit’s operating frequency. An-

other factor affecting capacitor performance is temperature. Fig-

ure 19 illustrates the temperature effect on various capacitors.

Aluminium electrolytic capacitors lose their capacitance at

low temperatures and their ESR increases considerably. Some

capacitor technologies do offer improved performance over

temperature; for example, certain tantalum capacitors provide

good low temperature ESR but at a higher cost. Table II pro-

vides the ratings for different types of capacitor technologies to

help the designer select the right capacitors for the application.

ESR capacitors such as solid tantalum and multilayer ceramic

capacitors are recommended to minimize voltage loss at high

currents. Table III shows a partial list of the recommended low

ESR capacitor manufacturers.

Input Capacitor

A small 1

µF input bypass capacitor, preferably with low ESR,

such as tantalum or multilayer ceramic, is recommended to

reduce noise and supply transients and supply part of the peak

input current drawn by the ADP3610. A large capacitor is rec-

ommended if the input supply is connected to the ADP3610

through long leads, or if the pulse current drawn by the device

might affect other circuitry through supply coupling.

Output Capacitor

input voltage and pump capacitor voltage when CP is switched

Note that as the capacitor value increases beyond the point

where the dominant contribution to the output ripple is due to

added capacitance.

Multiple smaller capacitors can be connected in parallel to yield

lower ESR and potential cost savings. For lighter loads, propor-

tionally smaller capacitors are required. To reduce high fre-

quency noise, bypass the output with a 0.1

µF ceramic capacitor.

Pump Capacitor

The ADP3610 alternately charges CP to the input voltage when

it is switched in parallel with the input supply, and then trans-

connected to the output.

ALUMINUM

CERAMIC

TANTALUM

ORGANIC SEMIC

TEMPERATURE – C

10

1.0

0.01

–50

0

100

50

0.1

TANTALUM

ORGANIC SEMIC

CERAMIC

ALUMINUM

Figure 19. ESR vs. Temperature

Power Dissipation

The power dissipation of the ADP3610 circuit must be limited

so the junction temperature of the device does not exceed the

maximum junction temperature rating. Total power dissipation

is calculated as follows:

device power dissipation is:

× 0.32 + 3 × (0.014) = 163.6 mW

The proprietary thermal coastline package used in the ADP3610

has a thermal resistance of 102

°C/W. Therefore, the rise in

junction temperature for this application would be:

× 102°C/W = 16.7°C

General Board Layout Guidelines

Since the ADP3610’s internal switches turn on and off very fast,

good PC board layout practices are critical to ensure optimal

operation of the device. Improper layouts will result in poor load

regulation, especially under heavy loads. Following these simple

layout guidelines will improve output performance.

1. Use adequate ground and power traces or planes.

2. Use single point ground for device ground and input and

output capacitor grounds.

3. Keep external components as close to the device as possible.

4. Use short traces from the input and output capacitors to the

input and output pins respectively.

together for proper operation.