APU3048 View Datasheet(PDF) - Advanced Power Electronics Corp

Part Name

Description

Manufacturer

APU3048

DUAL SYNCHRONOUS PWM CONTROLLER CIRCUITRY AND LDO CONTROLLER

Advanced Power Electronics Corp 

APU3048

THEORY OF OPERATION

Introduction

The APU3048 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 is con-

figured as two independent controllers. The timing of the

IC is provided through an internal oscillator circuit. These

are two out of phase oscillators.

Soft-Start

The APU3048 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 and VcH2 rise

above their threshold and generates the Power On Re-

set (POR) signal. Soft-start function operates by sourc-

ing an internal current to charge an external capacitor to

about 3V. Initially, the soft-start function clamps the E/

A’s output of the PWM converter. As the charging volt-

age of the external capacitor ramps up, the PWM sig-

nals increase from zero to the point the feedback loop

takes control.

Out of Phase Operation

The APU3048 drives its two output stages 1808 out of

phase. In application with single input voltage, the out of

phase operation reduces the input ripple current. This

results in much smaller RMS current in the input ca-

pacitor and reduction of input capacitors.

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.

Short-Circuit Protection

The outputs are protected against the short circuit. The

APU3048 protects the circuit for shorted output by sens-

ing the output voltages. The APU3048 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.

APPLICATION INFORMATION

Design Example:

The following example is a typical application for APU3048

in current sharing mode. The schematic is Figure 9 on

page 12.

For Switcher

VIN1 = 12V

VOUT1 = 3.3V

IOUT1 = 4A

VIN2 = 5V

VOUT2 = 1.8V

IOUT2 = 4A

DVOUT = 75mV

fS = 200KHz

For Linear Regulator

VIN3 = 3.3V

VOUT3 = 2.5V

IOUT3 = 2A

PWM Section

( ) VOUT1 = VREF3

R6

1+ R8

---(1)

When an external resistor divider is connected to the

output as shown in Figure 3.

VOUT1

APU3048

R6

Fb1

R8

Figure 3 - Typical application of the APU3048 for

programming the output voltage.

Output Voltage Programming

Output voltage is programmed by reference voltage and

external voltage divider. The Fb1 pin is the inverting input

of the error amplifier, which is internally referenced to

1.25V. The divider is ratioed to provide 1.25V at the Fb1

pin when the output is at its desired value. The output

voltage is defined by using the following equation:

Equation (1) can be rewritten as:

( ) R6 = R8 3 VOUT1 - 1

VREF

Will result to:

VOUT1=3.3V

VREF=1.25V

R8=1K, R6=1.64K

VOUT2=1.8V

VREF=1.25V

R15=1K, R14=442V

5

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