TOP250F-TL datasheet(5/52 Pages) POWERINT

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TOP242-250

12/04

TOPSwitch-GX

Family Functional

Description

Like TOPSwitch, TOPSwitch-GX is an integrated switched

mode power supply chip that converts a current at the control

input to a duty cycle at the open drain output of a high voltage

power MOSFET. During normal operation the duty cycle

of the power MOSFET decreases linearly with increasing

CONTROL pin current as shown in Figure 7.

In addition to the three terminal TOPSwitch features, such as

the high voltage start-up, the cycle-by-cycle current limiting,

loop compensation circuitry, auto-restart, thermal shutdown,

theTOPSwitch-GXincorporatesmanyadditionalfunctionsthat

reduce system cost, increase power supply performance and

design ﬂexibility. A patented high voltage CMOS technology

allows both the high voltage power MOSFET and all the low

voltage control circuitry to be cost effectively integrated onto

a single monolithic chip.

Three terminals, FREQUENCY, LINE-SENSE, and

EXTERNAL CURRENT LIMIT (available in Y, R or F

package) or one terminal MULTI-FUNCTION (available in P

or G package) have been added to implement some of the new

functions. These terminals can be connected to the SOURCE

pin to operate the TOPSwitch-GX in a TOPSwitch-like three

terminal mode. However, even in this three terminal mode, the

TOPSwitch-GX

offers many new transparent features that do

not require any external components:

1. A fully integrated 10 ms soft-start limits peak currents

and voltages during start-up and dramatically reduces or

eliminates output overshoot in most applications.

2. DC

MAX of 78% allows smaller input storage capacitor, lower

input voltage requirement and/or higher power capability.

3. Frequency reduction at light loads lowers the switching

lossesandmaintainsgoodcrossregulationinmultipleoutput

supplies.

4. Higher switching frequency of 132 kHz reduces the

transformer size with no noticeable impact on EMI.

5. Frequency jittering reduces EMI.

6. Hysteretic over-temperature shutdown ensures automatic

recovery from thermal fault. Large hysteresis prevents

circuit board overheating.

7. Packages with omitted pins and lead forming provide large

drain creepage distance.

8. Tighter absolute tolerances and smaller temperature

variations on switching frequency, current limit and PWM gain.

The LINE-SENSE (L) pin is usually used for line sensing by

connecting a resistor from this pin to the rectiﬁed DC high

voltage bus to implement line overvoltage (OV), under-voltage

(UV) and line feed-forward with DC

MAX reduction. In this

mode,thevalueoftheresistordeterminestheOV/UVthresholds

and the DC

MAX is reduced linearly starting from a line voltage

above the under-voltage threshold. See Table 2 and Figure 11.

The pin can also be used as a remote ON/OFF and a

synchronization input.

The EXTERNAL CURRENT LIMIT (X) pin is usually used

to reduce the current limit externally to a value close to the

operating peak current, by connecting the pin to SOURCE

through a resistor. This pin can also be used as a remote

ON/OFF and a synchronization input in both modes. See

Table 2 and Figure 11.

For the P or G packages the LINE-SENSE and EXTERNAL

CURRENTLIMITpin functions are combined on one MULTI-

FUNCTION (M) pin. However, some of the functions become

mutually exclusive as shown in Table 3.

The FREQUENCY (F) pin in the Y, R or F package sets the

switching frequency to the default value of 132 kHz when

connected to SOURCE pin. A half frequency option of

66 kHz can be chosen by connecting this pin to CONTROL pin

instead. Leaving this pin open is not recommended.

PI-2633-011502

C (mA)

TOP242-5 1.6 2.0

TOP246-9 2.2 2.6

TOP250

2.4 2.7

5.2 6.0

5.8 6.6

6.5 7.3

CD1

Auto-restart

L = 125 µA

L < IL(DC)

L = 190 µA

C (mA)

CD1

Auto-restart

132

Note: For P and G packages I

L is replaced with IM.

L < IL(DC)

L = 125 µA

Slope = PWM Gain

L = 190 µA

Figure 7. Relationship of Duty Cycle and Frequency to CONTROL

Pin Current.

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