ADP1032ACPZ-5-R7 datasheet(32/37 Pages) AD

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ADP1032

Data Sheet

Rev. 0 | Page 32 of 37

Maximum Output Current Calculation

The maximum output power and current that can be achieved

from the flyback output depends on a number of variables within

the regulator. These variables include the transformer choice,

the operating frequency, and the rectifier diode choice. The

flyback regulator output is the supply to the buck regulator that

drives VOUT2. Determine the maximum output power capability by

PVOUT1 (MAX) = 0.5 × (IPEAK2 − (IPEAK − IAC/2)2) × LPRI × fSW × η

where:

PVOUT1 (MAX) is the maximum output power from VOUT1.

η is the expected efficiency of the flyback regulator.

The lower limit of the flyback current-limit threshold, ILIM(FLYBACK),

limits the maximum IPEAK. However, it is not recommended to

operate at this level to avoid unwanted current-limit events due to

variation in transformer inductance, efficiency, flyback switching

frequency, and rectifier diode forward voltage drop. If the load on

the flyback causes the current limit to trip, the output voltage may

not regulate as expected. It is recommended to choose a peak

operating current with a built-in margin for the variations

mentioned or to calculate the maximum output power or output

load using the worst case transformer inductance, efficiency,

diode forward voltage drop, and flyback switching frequency.

Calculate the maximum load current on VOUT1 by

IVOUT1 (MAX) = PVOUT1 (MAX)/VOUT1

where IVOUT1 (MAX) is the maximum output current from VOUT1.

BUCK REGULATOR COMPONENTS SELECTION

Inductor

The value of the inductor for the ADP1032 buck regulator

affects the efficiency and the output voltage ripple. Larger value

inductors typically improve efficiency. However, for a given

package size, as load increases, the dc resistance (DCR) and core

losses eventually have an increasing negative impact on efficiency.

Using a smaller value inductor reduces output voltage ripple but

can decrease the overall efficiency due to increased switching

losses.

Output Capacitor

The output capacitor selection affects the output ripple voltage,

load step transient, and the loop stability of the regulator. A 4.7 µF

capacitor is recommended as a balance between performance and

size, but a larger capacitor reduces output ripple.

Table 17. Transformer Selection

Part Number

Manufacturer

Turns

Ratio1

Primary

Saturation

Current2

(mA)

Leakage

Inductance

(µH)

Isolation

Voltage3

(V rms)

Size, Length × Width

× Height, (mm)

Inductance

(µH)

Resistance

(Ω)

ZA9644-AE

Coilcraft

1:1

470

1.8

490

3.8 maximum

2000

10.92 × 9.25 × 10

750317986R6A

Würth Elektronik

1:1

470

1.27

480

3.5 typical,

7 maximum

1500

10.8 × 13.35 × 9.76

750318257R6A

Würth Elektronik

1:1

470

1.56

550

1.0 typical,

2.0 maximum

1500

16 × 16.8 × 7.62

ZA9384-AL

Coilcraft

1:1

470

1.1

800

4.0

2000

15.3 × 16.5 × 6.7

750318377R6A

Würth Elektronik

1:1

470

1.42

470

0.8 typical,

1.6 maximum

1500

17.78 × 22.35 × 8.89

751318463R6A

Würth Elektronik

1:1

470

1.22

450

0.5 typical,

1.0 maximum

Functional

isolation

10.8 × 13.35 × 9.76

Turns ratio between the primary and secondary coils.

20% drop from initial.

1 minute duration. Basic insulation.

Table 18. Buck Regulator Recommended Inductors

Part Number

Manufacturer

Inductance (µH)

DC Resistance (Ω)

Saturation Current1 (mA)

Size, Length ×

Width × Height, (mm)

744043101

Würth Elektronik

100

0.55

290

4.8 × 4.8 × 2.8

XFL3012-104MEB

Coilcraft

100

2.63

280

3.2 × 3.2 × 1.3

LQH3NPN101MMEL

Murata

100

1.59

260

3 × 3 × 1.4

SRN3015-101M

Bourns

100

2.92

270

3 × 3 × 1.5

SRU2016-101Y

Bourns

100

4.9

150

2.8 × 2.8 × 1.65

XFL2006-104MEB

Coilcraft

100

11.1

115

2 × 2 × 0.6

30% drop in inductance.

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