ADP1034ACPZ-1-R7 datasheet(33/41 Pages) AD

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Data Sheet

ADP1034

APPLICATIONS INFORMATION

analog.com

Rev. 0 | 33 of 41

Table 18. Recommended Feedback Resistor Values for Inverting Regulator

Target VOUT3 (V)

Inverting Regulator

RFT3 (MΩ)

RFB3 (kΩ)

Calculated VOUT3 (V)

−2

0.130

86.6

−2.000

−6

0.715

110

−6.000

−9

1.24

121

−8.998

−12

1.54

110

−12.000

−15

2.15

121

−15.015

−24

3.48

120

−24.000

Capacitor Selection

Higher output capacitor values reduce the output voltage ripple and

improve the load transient response. When choosing this value, it

is also important to account for the loss of capacitance due to the

output voltage dc bias.

Ceramic capacitors are manufactured with a variety of dielectrics,

each with a different behavior over temperature and applied volt-

age. Capacitors must have a dielectric adequate to ensure the

minimum capacitance over the necessary temperature range and

dc bias conditions. X5R or X7R dielectrics with voltage ratings of

25 V to 50 V (depending on output) are recommended for optimal

performance. Y5V and Z5U dielectrics are not recommended for

use with any dc-to-dc converter because of their poor temperature

and dc bias characteristics.

Calculate the worst case capacitance accounting for capacitor

variation over temperature, component tolerance, and voltage using

the following equation:

CEFFECTIVE = CNOMINAL × (1 − Tempco) × (1 − DCBIASCO) × (1 −

Tolerance)

where:

CEFFECTIVE is the effective capacitance at the operating voltage.

CNOMINAL is the nominal capacitance shown in the capacitor data

sheet.

Tempco is the worst case capacitor temperature coefficient.

DCBIASCO is the dc bias coefficient derating at the output voltage.

Tolerance is the worst case component tolerance.

To guarantee the performance of the device, it is imperative to

evaluate the effects of dc bias, temperature, and tolerances on the

behavior of the capacitors for each application.

Capacitors with lower effective series resistance (ESR) and effec-

tive series inductance (ESL) are preferred to minimize voltage

ripple.

FLYBACK REGULATOR COMPONENTS

SELECTION

Input Capacitor

An input capacitor must be placed between the VINP pin and

ground. Ceramic capacitors greater than or equal to 4.7 µF over

temperature and voltage are recommended. The input capacitor

reduces the input voltage ripple caused by the switching current.

Place the input capacitor as close as possible to the VINP and

PGNDP pins to reduce input voltage spikes. The voltage rating

of the input capacitor must be greater than the maximum input

voltage.

Output Capacitor

Higher output capacitor values reduce the output voltage ripple and

improve load transient response. When choosing this value, it is

also important to account for the loss of capacitance due to the

output voltage dc bias. A 10 μF capacitor is recommended as a

balance between performance and size.

Ripple Current vs. Capacitor Value

The output capacitor value must be chosen to minimize the output

voltage ripple while considering the increase in size and cost of a

larger capacitor. Use the following equation to calculate the output

capacitance:

COUT = (LPRI × ISWP2)/(2 × VOUT1 × ΔVOUT1)

where:

COUT is the capacitance of the flyback output capacitor.

LPRI is the primary inductance of the transformer.

ISWP is the peak switch current.

VOUT1 is the flyback regulator output voltage.

ΔVOUT1 is the allowable flyback regulator output ripple.

Schottky Diode

A Schottky diode with low junction capacitance is recommended

for D1. At higher output voltages and especially at higher switching

frequencies, the junction capacitance is a significant contributor to

efficiency. Choose an output diode with a forward current rating

(IF) that is greater than the maximum load requirement and with a

reverse voltage rating (VR) that is greater than the summation of

the maximum supply voltage (VVINP_MAX) and the maximum output

voltage (VOUT1_MAX).

Transformer

The transformer used with the ADP1034 is an important component

within the system, in terms of efficiency and maximum output

power capability. Analog Devices worked with a number of leading

magnetic component suppliers to develop transformer designs for

use with the ADP1034. These designs are listed in Table 19. A

number of factors must be taken into account when designing a

transformer for use with the ADP1034.

Turn Ratio

The ADP1034 requires the use of a transformer with a primary to

secondary turn ratio of 1:1 to start up properly.

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