APU3046 View Datasheet(PDF) - Advanced Power Electronics Corp

Part Name

Description

Manufacturer

APU3046

DUAL SYNCHRONOUS PWM CONTROLLER WITH CURRENT SHARING CIRCUITRY AND LDO CONTROLLER

Advanced Power Electronics Corp 

APU3046

For higher efficiency, a low ESR capacitor is recom-

mended.

For VIN1=5V, choose two Poscap from Sanyo

6TPB330M (6.3V, 330mF, 40mV, 3A)

For VIN2=12V, choose two 16TPB47M (16V, 47mF,

70mV, 1.4A).

Output Capacitor Selection

The criteria to select the output capacitor is normally

based on the value of the Effective Series Resistance

(ESR). In general, the output capacitor must have low

enough ESR to meet output ripple and load transient

requirements, yet have high enough ESR to satisfy sta-

bility requirements. The ESR of the output capacitor is

calculated by the following relationship:

For the buck converter, the inductor value for desired

operating ripple current can be determined using the fol-

lowing relation:

Di

1

VOUT

VIN - VOUT = L3Dt ; Dt = D3 fS ; D = VIN

L

=

(V IN

-

VOUT)3

VOUT

VIN3Di3fS

---(6)

Where:

VIN = Maximum Input Voltage

VOUT = Output Voltage

∆i = Inductor Ripple Current

fS = Switching Frequency

∆t = Turn On Time

D = Duty Cycle

For Di1=30% of I1, we get: L1=2.18mH

For Di2=30% of I2, we get: L2=2.7mH

DVO

ESR [ DIO

---(5)

Where:

DVO = Output Voltage Ripple

DIO = Output Current

DVO=75mV and DIO=10A, result to ESR=7.5mV

The Sanyo TPC series, Poscap capacitor is a good choice.

The 6TPC150M 150mF, 6.3V has an ESR 40mV. Se-

lecting six of these capacitors in parallel, results to an

ESR of ≅ 7mV which achieves our low ESR goal.

The Coilcraft DO5022HC series provides a range of in-

ductors in different values and low profile for large cur-

rents.

For L1 choose: DO5022P-222HC (2.2mH,12A)

For L2 choose: DO5022P-332HC (3.3mH,10A)

Power MOSFET Selection

The selections criteria to meet power transfer require-

ments is based on maximum drain-source voltage (VDSS),

gate-source drive voltage (VGS), maximum output cur-

rent, On-resistance RDS(ON) and thermal management.

The capacitor value must be high enough to absorb the

inductor's ripple current. The larger the value of capaci-

tor, the lower will be the output ripple voltage.

The resulting output ripple current is smaller then each

channel ripple current due to the 1808 phase shift. These

currents cancel each other. The cancellation is not the

maximum because of the different duty cycle for each

channel.

Inductor Selection

The inductor is selected based on output power, operat-

ing frequency and efficiency requirements. Low induc-

tor value causes large ripple current, resulting in the

smaller size, but poor efficiency and high output noise.

Generally, the selection of inductor value can be reduced

to desired maximum ripple current in the inductor (∆i);

the optimum point is usually found between 20% and

50% ripple of the output current.

The MOSFET must have a maximum operating voltage

(VDSS) exceeding the maximum input voltage (VIN).

The gate drive requirement is almost the same for both

MOSFETs. Caution should be taken with devices at very

low VGS to prevent undesired turn-on of the complemen-

tary MOSFET, which results a shoot-through current.

The total power dissipation for MOSFETs includes con-

duction and switching losses. For the Buck converter

the average inductor current is equal to the DC load cur-

rent. The conduction loss is defined as:

PCOND (Upper Switch) = IL2OAD 3 RDS(ON) 3 D 3 q

PCOND (Lower Switch) = IL2OAD 3 RDS(ON) 3 (1 - D) 3 q

q = RDS(ON) Temperature Dependency

The total conduction loss is defined as:

PCON(TOTAL)=PCON(Upper Switch)q + PCON(Lower Switch)q

7/18

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