ML4818 datasheet(9/12 Pages) MICRO-LINEAR

9 / 12 page

ML4818

UNDER-VOLTAGE LOCKOUT

On power up, when VCC is below 16V, the IC draws very

little current (1.1mA typ.) and VREF is disabled. When VCC

rises above 16V, the IC becomes active and VREF is

enabled and will stay in that condition until VCC falls

below 10.2V. (see Figure 12).

INHIBIT

OUTPUTS

–

INTERNAL

BIAS

TO LOGIC

CIRCUITS

VREF

VCC

POWER

DOWN

Figure 12. Under-Voltage Lockout and

Reference Circuits.

Figure 13. Supply Current vs. Temperature (

°C).

–75

–25

125

175

TEMPERATURE

Figure 15.

θJA as a Function of I (see figure 15).

I : HEAT SINK DIMENSION (INCHES)

0.2

0.4

0.6

0.8

1.2

1.4

1.6

1.8

Figure 14. PC Board Copper Area Used as a Heat Sink.

APPLICATIONS

The application circuit shown in Figure 16 features the

ML4818 in a primary-side controlled voltage mode

application with voltage feed-forward. Input voltage is

rectified 120VAC (nominal). Feed-forward is provided by

the RAMP pin via the resistor connected to the high

voltage input. Current is sensed through sense transformer

T4.

0.555"

THERMAL INFORMATION

The ML4818 is offered in a Power DIP package. This

package features improved thermal conduction through

the leadframe. Much of the heat is conducted through the

center 4 grounded leads. Thermal dissipation can be

improved with this package by using copper area on the

board to function as a heat sink. Increasing this area can

reduce the

θJA (see figures 14 and 15), increasing the

power handling capability of the package. Additional

improvement may be obtained by using an external heat

sink (available from Staver).

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