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

THEORY OF OPERATION

Introduction

The APU3046 is designed for multi-outputs applications.

It includes two synchronous buck controllers and a lin-

ear regulator controller. The two synchronous controller

operates with fixed frequency voltage mode and can be

configured as two independent controller or 2-phase con-

troller with current sharing. The timing of the IC is pro-

vided through an internal oscillator circuit. These are two

out of phase oscillators and can be programmed by us-

ing an external resistor from 200KHz to 400KHz per

phase. Figure 11 shows switching frequency versus ex-

ternal resistor.

Independent Mode

In this mode the APU3046 provides two independent out-

puts with either common or different input voltages. The

output voltage of the individual channel is set and con-

trolled by the output of the error amplifier, this is the

amplified error signal from the sensed output voltage and

the reference voltage. This voltage is compared to the

ramp signal and generates fixed frequency pulses of vari-

able duty-cycle, which drives the two N-channel exter-

nal MOSFETs.

Current Sharing Mode

In the current sharing mode, the two converter’s outputs

tied together and provide one single output (see Figure

1). In this mode, one control loop acts as a master and

sets the output voltage as a regular Voltage Mode buck

controller and the other control loop acts as a slave and

monitors the current information for current sharing. The

current sharing is programmable and sets by using two

external resistors in output currents’ path. The slave's

error amplifier, error amplifier 2 (see Block Diagram) mea-

sures the voltage drops across the current sense resis-

tors, the differential of these signals is amplified and

compared with the ramp signal and generate the fixed

frequency pulses of variable duty cycle to match the

output currents.

Soft-Start

The APU3046 has a programmable soft start to control

the output voltage rise and limit the current surge at the

start-up. To ensure correct start-up, the soft-start se-

quence initiates when the Vcc, VcH1, VcH2, VccLDO

and VSEN33 rise above their threshold and generates the

Power On Reset (POR) signal. Soft-start function oper-

ates by sourcing an internal current to charge an exter-

nal capacitor to about 3V. Initially, the soft-start function

clamps the E/A’s output of the PWM converter. As the

charging voltage of the external capacitor ramps up, the

PWM signals increase from zero to the point the feed-

back loop takes control.

Shutdown

The converter can be shutdown by pulling the soft-start

pin below 0.5V. This can be easily done by using an

external small signal transistor. During shutdown the

MOSFET drivers and the LDO controller turn off.

Power Good

The APU3046 provides a power good signal. This is an

open collector output and it is pulled low if the output

voltages are not within the specified threshold. This pin

can be left floating if not used.

Short-Circuit Protection

The outputs are protected against the short circuit. The

APU3046 protects the circuit for shorted output by sens-

ing the output voltages. The APU3046 shuts down the

PWM signals and LDO controller, when the output volt-

ages drops below the set values.

Under-Voltage Lockout

The under-voltage lockout circuit assures that the

MOSFET driver outputs and LDO controller remain in

the off state whenever the supply voltages drop below

set parameters. Normal operation resumes once the

supply voltages rise above the set values.

Out of Phase Operation

The APU3046 drives its two output stages 180o out of

phase. In 2-phase configuration, the two inductor ripple

currents cancel each other and result to a reduction of

the output current ripple and contribute to a smaller out-

put capacitor for the same ripple voltage requirement.

Frequency Synchronization

The APU3046 can be synchronized with an external clock

signal. The synchronizing pulses must have a minimum

pulse width of 100ns. If the sync function is not used,

the Sync pin can be either connected to ground or be

floating.

In application with single input voltage, the 2-phase con-

figuration reduces the input ripple current. This results in

much smaller RMS current in the input capacitor and

reduction of input capacitor.

5/18

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