PJ3842BCS Просмотр технического описания (PDF) - Promax Johnton

Номер в каталоге

Компоненты Описание

производитель

PJ3842BCS

High Performance Current Mode Controller

Promax Johnton 

PJ3842B / PJ3843B

High Performance Current Mode Controller

FIGURE 18-TIMING DIAGRAM

UNDERVOLTAGE LOCKOUT

Two undervoltage lockout comparators have been

incorporated to guarantee that the IC is fully functional before

the output stage is enabled. The positive power supply

terminal (VCC) and the reference output (Vref) are each

monitored by separate comparators.Each has built-in

hysteresis to prevent erratic output behavior as their respective

thresholds are crossed. The large hysteresis and low start-up

current of the PJ3842B makes it ideally suited in off-line

converter applications where efficient bootstrap start-up

technique (Figure 33). 36 V zener is connected as a shunt

regulator from VCC to ground.Its purpose is to protect the IC

from excessive voltage that can occur during system start-up.

The minimum operating voltage for the PJ3842B is 11V.

Output

These devices contain a single totem pole output stage

that was specifically designed for direct drive of power

MOSFET’s. It is capable of up to ±1.0A peak drive current

and has a typical rise and fall time of 50 ns with a 1.0nF load.

Additional internal circuitry has been added to keep the

Output in a sinking mode whenever an undervoltage lockout

is active.This characteristic eliminates the need for an external

pull-down resistor.

The SOP-8 surface mount package provides separate pins

for Vc(output supply) and Power Ground.Proper

implementation will significantly reduce the level of

switching transient noise imposed on the control circuitry.

This becomes particularly useful when reducing the Ipk(max)

clamp level.The separate Vc supply input allows the designer

added fiexlbility in tailoring the drive voltage independent of

Vcc.A zener clamp is typically connected to this input when

driving power MOSFETs in systems where Vcc is greater

than 20V. Figure 25 shows proper power and control ground

connections in a current sensing power MOSFET application.

Reference

The 5.0V bandgap reference is trimmed to±2.0% on the

PJ3842B.Its promary purpose to supply charging current to

the oscillator timing capacitor.The reference has short circuit

protection and is capable of providing in excess of 20mA for

powering additional control system circuitry.

7-14

2004/11.Rev B

Share Link: