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APU3146

DUAL SYNCHRONOUS PWM CONTROLLER WITH CURRENT SHARING CIRCUITRY AND AUTO-RESTART

Advanced Power Electronics Corp 

APU3146

FUNCTIONAL DESCRIPTION

Introduction

The APU3146 is versatile device for high performance Buck

converters. It is included of two synchronous Buck con-

trollers which can be operated both in two independent

mode or in 2-phase mode.

The timing of the IC is provided through an internal oscil-

lator circuit. These are two out-of-phase oscillators that

can be programmed up to 400KHz per phase.

Supply Voltage

Vcc is the supply voltage for internal controller. The op-

erating range is from 4.5V to 16V. It also is fed to the

internal LDO. When Vcc is below under-voltage thresh-

old, all MOSFET drivers will be turned off.

information for current sharing. The voltage drops across

the current sense resistors (or DCR of inductors) are

measured and their difference is amplified by the slave

error amplifier and compared with the ramp signal to

generate the PWM pulses to match the output current.

In this mode the SS2 pin should be floating.

PWM Comp1

PWM Comp2

APU3146

Master E/A

Comp

0.8V

Fb1

L1

RL1

VOUT

R1 C1

Internal Regulator

The regulator powers directly from VCC and generates a

regulated voltage (Typ. 6.2V@50mA). The output is pro-

tected for short circuit. This voltage can be used for charge

pump circuitry as describe in Figure12.

VP2

FB2

Slave E/A

L2

RL2

R2 C2

Input Supplies UnderVoltage LockOut

The APU3146 UVLO block monitors three input voltages

(VCC, VCH1 and VCH2) to ensure reliable start up. The

MOSFET driver output turn off when any of the supply

voltages drops below set thresholds. Normal operation

resumes once the supply voltages rise above the set

values.

Independent Mode

In this mode the APU3146 provides control to two inde-

pendent output power supplies with either common or

different input voltages. The output voltage of each indi-

vidual channel is set and controlled by the output of the

error amplifier, which is the amplified error signal from

the sensed output voltage and the reference voltage. The

error amplifier output voltage is compared to the ramp

signal thus generating fixed frequency pulses of variable

duty-cycle, which are applied to the FET drivers, Fig-

ure18 shows a typical schematic for such application.

Figure 4 - Loss-less inductive current sensing

and current sharing.

In the diagram, L1 and L2 are the output inductors. RL1

and RL2 are inherent inductor resistances. The resistor

R1 and capacitor C1 are used to sense the average in-

ductor current. The voltage across the capacitors C1

and C2 represent the average current flowing into resis-

tance RL1 and RL2. The time constant of the RC network

should be equal or at most three times larger than the

time constant L /R .

1 L1

R1×C1=(1~3)× L1

RL1

---(1)

2-Phase Mode

This feature allows to connect both outputs together to

increase current handling capability of the converter to

support a common load. The current sharing can be done

either using external resistors or sensing the DCR of

inductors (see Figure 4). In this mode, one control loop

acts as a master and sets the output voltage as a regu-

lar Voltage Mode Buck controller and the other control

loop acts as a slave and monitors the current

Figure 5 - 30A Current Sharing using Inductor sensing

(5A/Div)

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