• Output capacitor of 1 μF, ESR of 0.1 Ω

• Capacitor discharge time 1% of 800-kHz (ripple frequency)

tDIS = 0.0125 μs

τ = C × RLOAD

τ = 1 × 10-6 × 12.5 = 12.5 μs

VDIS = VO(1 – EXP(–tDIS / τ))

VDIS = 5 mV

By contrast, the voltage dropped because of ESR:

VESR = ILOAD × ESR

VESR = 40 mV

Ripple voltage = 45 mV

8.2.8 Dual DCP02 Output Voltage

The voltage output for dual DCP02 devices is half wave rectified; therefore, the discharge time is 1.25 μs.

Repeating the above calculations using the 100% load resistance of 25 Ω (0.2 A per output), the results are:

τ = 25 μs

tDIS = 1.25 μs

VDIS = 244 mV

VESR = 20 mV

Ripple Voltage = 266 mV

This time, it is the capacitor discharging that contributes to the largest component of ripple. Changing the output

filter to 10 μF, and repeating the calculations, the result is:

Ripple Voltage = 45 mV

This value is composed of almost equal components.

The previous calculations are offered as a guideline only. Capacitor parameters usually have large tolerances

and can be susceptible to environmental conditions.

8.2.9 Optimizing Performance

Optimum performance can only be achieved if the device is correctly supported. The very nature of a switching

converter requires power to be instantly available when it switches on. If the converter has DMOS switching

transistors, the fast edges will create a high current demand on the input supply. This transient load placed on

the input is supplied by the external input decoupling capacitor, thus maintaining the input voltage. Therefore, the

input supply does not see this transient (this is an analogy to high-speed digital circuits). The positioning of the

capacitor is critical and must be placed as close as possible to the input pins and connected by a low-impedance

path.

The optimum performance primarily depends on two factors:

• Connection of the input and output circuits for minimal loss.

• The ability of the decoupling capacitors to maintain the input and output voltages at a constant level.

Power Supply Recommendations

The DCP02 is a switching power supply, and as such can place high peak current demands on the input supply.

In order to avoid the supply falling momentarily during the fast switching pulses, ground and power planes must

be used to connect the power to the input of DCP02. If this connection is not possible, then the supplies must be

connected in a star formation with the traces made as wide as possible.

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DCP021212D, DCP021515, DCP022405, DCP022405D, DCP022415D

SBVS011N – MARCH 2000 – REVISED APRIL 2020

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