Power Integrations TOP243P, TOP243G, TOP243G-TL, TOP242Y, TOP242R-TL Datasheet

®

®

TOP242-249

TOPSwitch -GX

Family

Extended Power, Design Flexible,

EcoSmart

®

, Integrated Off-line Switcher

July 2001

Figure 1. Typical Flyback Application.

PRODUCT

3

Adapter

1

Open

Frame

2

Open

Frame

2

OUTPUT POWER TABLE

Table 1. Notes: 1. Typical continuous power in a non-ventilated
enclosed adapter measured at 50 °C ambient. Assumes 1 sq. in. of
2 oz. copper heat sink area for R package. 2. Maximum practical
continuous power in an open frame design at 50 °C ambient. See
Key Applications for detailed conditions. Assumes 3 sq. in. of 2 oz.
copper heat sink area for R package. 3. See Part Ordering Information.

4. 230 VAC or 100/115 VAC with doubler.

PI-2632-060200

AC

IN

DC

OUT

D

S

C

TOPSwitch-GX

CONTROL

L

+

-

FX

230 VAC ±15%

4

Adapter

1

85-265 VAC

9 W 15 W 6.5 W 10 W
10 W 22 W 7 W 14 W
10 W 22 W 7 W 14 W

13 W 25 W 9 W 15 W
20 W 43 W 15 W 23 W
13 W 45 W 15 W 30 W

16 W 30 W 11 W 20 W
28 W 52 W 18 W 28 W
30 W 65 W 20 W 45 W

33 W 58 W 20 W 32 W
40 W 85 W 26 W 60 W

37 W 65 W 24 W 36 W
60 W 125 W 40 W 90 W

41 W 73 W 26 W 43 W
85 W 165 W 55 W 125 W

43 W 78 W 28 W 48 W

105 W 205 W 70 W 155 W

45 W 82 W 30 W 52 W

120 W 250 W 80 W 180 W

Product Highlights

Lower System Cost, High Design Flexibility

• Extended power range to 250 W

• Features eliminate or reduce cost of external components

• Fully integrated soft-start for minimum stress/overshoot

• Externally programmable accurate current limit

• Wider duty cycle for more power, smaller input capacitor

• Separate line sense and current limit pins on Y/R packages

• Line under-voltage (UV) detection: no turn off glitches

• Line overvoltage (OV) shutdown extends line surge limit

• Line feed forward with maximum duty cycle (DC

MAX

)

reduction rejects line ripple and limits DC

MAX

at high line

• Frequency jittering reduces EMI and EMI filtering costs

• Regulates to zero load without dummy loading

• 132 kHz frequency reduces transformer/power supply size

• Half frequency option in Y/R packages for video applications

• Hysteretic thermal shutdown for automatic fault recovery

• Large thermal hysteresis prevents PC board overheating

EcoSmart

- Energy Efficient

• Extremely low consumption in remote off mode
(80 mW @ 110 VAC, 160 mW @ 230 VAC)

• Frequency lowered with load for high standby efficiency

• Allows shutdown/wake-up via LAN/input port

Description

TOPSwitch-GX uses the same proven topology as TOPSwitch,
cost effectively integrating the high voltage power MOSFET,
PWM control, fault protection and other control circuitry onto
a single CMOS chip. Many new functions are integrated to
reduce system cost and improve design flexibility, performance
and energy efficiency.

Depending on package type, the TOPSwitch-GX family has
either 1 or 3 additional pins over the standard DRAIN, SOURCE
and CONTROL terminals. allowing the following functions:
line sensing (OV/UV, line feedforward/DC max reduction),
accurate externally set current limit, remote on/off, and
synchronization to an external lower frequency and frequency
selection (132 kHz/66 kHz).

All package types provide the following transparent features:
Soft-start, 132 kHz switching frequency (automatically reduced
at light load), frequency jittering for lower EMI, wider DC

MAX

,
hysteretic thermal shutdown and larger creepage packages. In
addition, all critical parameters (i.e. current limit, frequency,
PWM gain) have tighter temperature and absolute tolerance, to
simplify design and optimize system cost.

TOP242 P or G

TOP242 R
TOP242 Y

TOP243 P or G

TOP243 R
TOP243 Y

TOP244 P or G

TOP244 R
TOP244 Y

TOP245 R
TOP245 Y

TOP246 R
TOP246 Y

TOP247 R
TOP247 Y

TOP248 R
TOP248 Y

TOP249 R
TOP249 Y

TOP242-249

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Section List

Functional Block Diagram......................................................................................................................................... 3

Pin Functional Description........................................................................................................................................ 4

TOPSwitch-GX Family Functional Description ........................................................................................................5

CONTROL (C) Pin Operation .................................................................................................................................6

Oscillator and Switching Frequency .......................................................................................................................6

Pulse Width Modulator and Maximum Duty Cycle ................................................................................................. 7

Light Load Frequency Reduction............................................................................................................................7

Error Amplifier......................................................................................................................................................... 7

On-chip Current Limit with External Programmability.............................................................................................7

Line Under-Voltage Detection (UV) ........................................................................................................................ 8

Line Overvoltage Shutdown (OV)...........................................................................................................................8

Line Feed Forward with DC

MAX

Reduction ..............................................................................................................8

Remote ON/OFF and Synchronization................................................................................................................... 9

Soft-Start ................................................................................................................................................................9

Shutdown/Auto-Restart ..........................................................................................................................................9

Hysteretic Over-Temperature Protection ................................................................................................................9

Bandgap Reference................................................................................................................................................9

High-Voltage Bias Current Source........................................................................................................................10

Using Feature Pins.................................................................................................................................................... 11

FREQUENCY (F) Pin Operation........................................................................................................................... 11

LINE-SENSE (L) Pin Operation............................................................................................................................ 11

EXTERNAL CURRENT LIMIT (X) Pin Operation ................................................................................................. 11

MULTI-FUNCTION (M) Pin Operation .................................................................................................................. 12

Typical Uses of FREQUENCY (F) Pin ......................................................................................................................15

Typical Uses of LINE-SENSE (L) and EXTERNAL CURRENT LIMIT (X) Pins.......................................................16

Typical Uses of MULTI-FUNCTION (M) Pin ............................................................................................................. 19

Application Examples............................................................................................................................................... 21

A High Efficiency, 30 W, Universal Input Power Supply........................................................................................21

A High Efficiency, Enclosed, 70 W, Universal Adapter Supply..............................................................................22

A High Efficiency, 250 W, 250 - 380 VDC Input Power Supply.............................................................................23

Multiple Output, 60 W, 185 - 265 VAC Input Power Supply..................................................................................24

Processor Controlled Supply Turn On/Of f ............................................................................................................ 25

Key Application Considerations ..............................................................................................................................27

TOPSwitch-II vs. TOPSwitch-GX..........................................................................................................................27

TOPSwitch-FX vs. TOPSwitch-GX.......................................................................................................................28

TOPSwitch-GX Design Considerations ................................................................................................................ 29

TOPSwitch-GX Layout Considerations.................................................................................................................31

Quick Design Checklist.........................................................................................................................................31

Design Tools ......................................................................................................................................................... 33

Product Specifications and Test Conditions.......................................................................................................... 34

Typical Performance Characteristics ...................................................................................................................... 41

Part Ordering Information ........................................................................................................................................45

Package Outlines ......................................................................................................................................................45

TOP242-249

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Figure 2a. Functional Block Diagram (Y or R Package).

PI-2641-061200

PI-2639-060600

Figure 2b. Functional Block Diagram (P or G Package).

PI-2631-061200

SHUTDOWN/

AUTO-RESTART

PWM

COMPARATOR

CLOCK

SAW

CONTROLLED

TURN-ON

GATE DRIVER

CURRENT LIMIT

COMPARATOR

INTERNAL UV

COMPARATOR

INTERNAL
SUPPLY

5.8 V

4.8 V

SOURCE (S)

SRQ

D

MAX

STOP

SOFT-

START

­+

CONTROL (C)

MULTI-

FUNCTION (M)

­+

5.8 V

I

FB

R

E

Z

C

V

C

+

-

LEADING

EDGE

BLANKING

÷ 8

1

HYSTERETIC

THERMAL

SHUTDOWN

SHUNT REGULATOR/

ERROR AMPLIFIER

+

-

DRAIN (D)

ON/OFF

SOFT

START

DC

MAX

V

BG

DC

MAX

V

BG

+ V

T

0

OV/UV

V

I (LIMIT)

CURRENT

LIMIT

ADJUST

LINE

SENSE

SOFT START

LIGHT LOAD
FREQUENCY
REDUCTION

STOP LOGIC

OSCILLATOR WITH JITTER

PI-2639-060600

SHUTDOWN/

AUTO-RESTART

PWM

COMPARATOR

CLOCK

SAW

HALF
FREQ.

CONTROLLED

TURN-ON

GATE DRIVER

CURRENT LIMIT

COMPARATOR

INTERNAL UV

COMPARATOR

INTERNAL
SUPPLY

5.8 V

4.8 V

SOURCE (S)

SRQ

D

MAX

STOP

SOFT­START

-

+

CONTROL (C)

LINE-SENSE (L)

EXTERNAL

CURRENT LIMIT (X)

FREQUENCY (F)

­+

5.8 V

1 V

I

FB

R

E

Z

C

V

C

+

-

LEADING

EDGE

BLANKING

÷ 8

1

HYSTERETIC

THERMAL

SHUTDOWN

SHUNT REGULATOR/

ERROR AMPLIFIER

+

-

DRAIN (D)

ON/OFF

SOFT

START

DC

MAX

V

BG

DC

MAX

V

BG

+ V

T

0

OV/UV

V

I (LIMIT)

CURRENT

LIMIT

ADJUST

LINE

SENSE

SOFT START

LIGHT LOAD
FREQUENCY
REDUCTION

STOP LOGIC

OSCILLATOR WITH JITTER

TOP242-249

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Pin Functional Description

DRAIN (D) Pin:

High voltage power MOSFET drain output. The internal start­up bias current is drawn from this pin through a switched high­voltage current source. Internal current limit sense point for
drain current.

CONTROL (C) Pin:

Error amplifier and feedback current input pin for duty cycle
control. Internal shunt regulator connection to provide internal
bias current during normal operation. It is also used as the
connection point for the supply bypass and auto-restart/
compensation capacitor.

LINE-SENSE (L) Pin: (Y or R package only)
Input pin for OV, UV, line feed forward with DC

MAX

reduction,
remote ON/OFF and synchronization. A connection to SOURCE
pin disables all functions on this pin.

EXTERNAL CURRENT LIMIT (X) Pin: (Y or R package only)
Input pin for external current limit adjustment, remote
ON/OFF, and synchronization. A connection to SOURCE pin
disables all functions on this pin.

MULTI-FUNCTION (M) Pin: (P or G package only)
This pin combines the functions of the LINE-SENSE (L) and
EXTERNAL CURRENT LIMIT (X) pins of the Y package into
one pin. Input pin for OV, UV, line feed forward with DC

MAX

reduction, external current limit adjustment, remote ON/OFF
and synchronization. A connection to SOURCE pin disables all
functions on this pin and makes TOPSwitch-GX operate in
simple three terminal mode (like TOPSwitch-II).

FREQUENCY (F) Pin: (Y or R package only)
Input pin for selecting switching frequency: 132 kHz if

Figure 3. Pin Configuration (top view).

PI-2509-040501

DC

Input

Voltage

+

-

DM

S

C

VUV = IUV x R

LS

V

OV = IOV x RLS

For RLS = 2 MΩ
V

UV

= 100 VDC

V

OV =

450 VDC

DC

MAX

@100 VDC = 78%

DC

MAX

@375 VDC = 38%

CONTROL

R

LS

2 MΩ

PI-2517-040501

DC

Input

Voltage

+

-

DM

S

C

For R

IL

= 12 kΩ

I

LIMIT

= 69%

CONTROL

R

IL

See fig. 55 for other
resistor values (R

IL

)

For R

IL

= 25 kΩ

I

LIMIT

= 43%

to select different
I

LIMIT

values

X

PI-2629-040501

DC

Input

Voltage

+

-

D

S

C

CONTROL

L

R

IL

R

LS

12 kΩ

2 MΩ

VUV = IUV x R

LS

V

OV = IOV x RLS

For RLS = 2 MΩ

DC

MAX

@100 VDC = 78%

DC

MAX

@375 VDC = 38%

For R

IL

= 12 kΩ

I

LIMIT

= 69%

See fig. 55 for other
resistor values (R

IL

)

to select different I

LIMIT

values

V

UV

= 100 VDC

V

OV

= 450 VDC

Figure 4. Y/R Package Line Sense and Externally Set Current

Limit.

Figure 5. P/G Package Line Sense.

Figure 6. P/G Package Externally Set Current Limit.

connected to SOURCE pin and 66 kHz if connected to
CONTROL pin. The switching frequency is internally set for
fixed 132 kHz operation in P and G packages.

SOURCE (S) Pin:

Output MOSFET source connection for high voltage power
return. Primary side control circuit common and reference point.

PI-2724-033001

Tab Internally
Connected to

SOURCE Pin

Y Package (TO-220-7C)

C

D

S
S

S

S

1 C

3 X
2 L

5 F
4 S

7 D

M

P Package (DIP-8B)

G Package (SMD-8B)

R Package

(TO-263-7C)

8

5

7

1

12345 7

CLX SF D

4

2

3

TOP242-249

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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, the
TOPSwitch-GX incorporates many additional functions that
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 or R 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

losses and maintains good cross regulation in multiple
output 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 vari-

ations 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, the value of the resistor determines the OV/UV thresholds
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
CURRENT LIMIT pin functions are combined on one MULTI­FUNCTION (M) pin. However, some of the functions become
mutually exclusive as shown in Table 3.

The FREQUENCY (F) pin in the Y or R 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-2633-060500

Duty Cycle (%)

IC (mA)

TOP242/5 1.6 2.0
TOP246/9 2.2 2.6

5.2 6.0

5.8 6.6

I

CD1

I

B

Auto-restart

IL = 125 µA

IL < I

L(DC)

IL = 190 µA

78

10

38

Frequency (kHz)

IC (mA)

30

I

CD1

I

B

Auto-restart

132

Note: For P and G packages IL is replaced with IM.

IL < I

L(DC)

I

L

= 125 µA

Slope = PWM Gain

IL = 190 µA

Figure 7. Relationship of Duty Cycle and Frequency to CONTROL

Pin Current.

TOP242-249

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August 8, 2000

PI-2545-082299

S1 S2 S6 S7 S1 S2 S6 S7S0

S1 S7

S0

S0

5.8 V

4.8 V

S7

0 V

0 V

0 V

V

LINE

V

C

V

DRAIN

V

OUT

Note: S0 through S7 are the output states of the auto-restart counter

2

1

2

3

4

0 V

~

~

~

~

~

~

~

~

~

~

S6 S7

~

~

~

~

~

~

~

~

V

UV

~

~

~

~

~

~

~

~

S2

~

~

CONTROL (C) Pin Operation

The CONTROL pin is a low impedance node that is capable of
receiving a combined supply and feedback current. During
normal operation, a shunt regulator is used to separate the
feedback signal from the supply current. CONTROL pin
voltage VC is the supply voltage for the control circuitry
including the MOSFET gate driver. An external bypass capacitor
closely connected between the CONTROL and SOURCE pins
is required to supply the instantaneous gate drive current. The
total amount of capacitance connected to this pin also sets the
auto-restart timing as well as control loop compensation.

When rectified DC high voltage is applied to the DRAIN pin
during start-up, the MOSFET is initially off, and the CONTROL
pin capacitor is charged through a switched high voltage current
source connected internally between the DRAIN and CONTROL
pins. When the CONTROL pin voltage VC reaches
approximately 5.8 V, the control circuitry is activated and the
soft-start begins. The soft-start circuit gradually increases the
duty cycle of the MOSFET from zero to the maximum value
over approximately 10 ms. If no external feedback/supply
current is fed into the CONTROL pin by the end of the soft-start,
the high voltage current source is turned off and the CONTROL
pin will start discharging in response to the supply current
drawn by the control circuitry. If the power supply is designed
properly, and no fault condition such as open loop or shorted
output exists, the feedback loop will close, providing external
CONTROL pin current, before the CONTROL pin voltage has
had a chance to discharge to the lower threshold voltage of
approximately 4.8 V (internal supply under-voltage lockout
threshold). When the externally fed current charges the
CONTROL pin to the shunt regulator voltage of 5.8 V, current

in excess of the consumption of the chip is shunted to SOURCE
through resistor RE as shown in Figure 2. This current flowing
through RE controls the duty cycle of the power MOSFET to
provide closed loop regulation. The shunt regulator has a finite
low output impedance ZC that sets the gain of the error amplifier
when used in a primary feedback configuration. The dynamic
impedance ZC of the CONTROL pin together with the external
CONTROL pin capacitance sets the dominant pole for the
control loop.

When a fault condition such as an open loop or shorted output
prevents the flow of an external current into the CONTROL pin,
the capacitor on the CONTROL pin discharges towards 4.8 V.
At 4.8 V, auto-restart is activated which turns the output
MOSFET off and puts the control circuitry in a low current
standby mode. The high-voltage current source turns on and
charges the external capacitance again. A hysteretic internal
supply under-voltage comparator keeps VC within a window of
typically 4.8 to 5.8 V by turning the high-voltage current source
on and off as shown in Figure 8. The auto-restart circuit has a
divide-by-8 counter which prevents the output MOSFET from
turning on again until eight discharge/charge cycles have elapsed.
This is accomplished by enabling the output MOSFET only
when the divide-by-8 counter reaches full count (S7). The
counter effectively limits TOPSwitch-GX power dissipation by
reducing the auto-restart duty cycle to typically 4%. Auto­restart mode continues until output voltage regulation is again
achieved through closure of the feedback loop.

Oscillator and Switching Frequency

The internal oscillator linearly charges and discharges an internal
capacitance between two voltage levels to create a sawtooth

Figure 8. Typical Waveforms for (1) Power Up (2) Normal Operation (3) Auto-restart (4) Power Down.

TOP242-249

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Figure 9. Switching Frequency Jitter. (Idealized V

DRAIN

waveform)

waveform for the pulse width modulator. This oscillator sets
the pulse width modulator/current limit latch at the beginning
of each cycle.

The nominal switching frequency of 132 kHz was chosen to
minimize transformer size while keeping the fundamental EMI
frequency below 150 kHz. The FREQUENCY pin (available
only in Y or R package), when shorted to the CONTROL pin,
lowers the switching frequency to 66 kHz (half frequency)
which may be preferable in some cases such as noise sensitive
video applications or a high efficiency standby mode. Otherwise,
the FREQUENCY pin should be connected to the SOURCE pin
for the default 132 kHz.

To further reduce the EMI level, the switching frequency is
jittered (frequency modulated) by approximately ±4 kHz at
250 Hz (typical) rate as shown in Figure 9. Figure 46 shows the
typical improvement of EMI measurements with frequency
jitter.

Pulse Width Modulator and Maximum Duty Cycle

The pulse width modulator implements voltage mode control
by driving the output MOSFET with a duty cycle inversely
proportional to the current into the CONTROL pin that is in
excess of the internal supply current of the chip (see Figure 7).
The excess current is the feedback error signal that appears
across RE (see Figure 2). This signal is filtered by an RC
network with a typical corner frequency of 7 kHz to reduce the
effect of switching noise in the chip supply current generated by
the MOSFET gate driver. The filtered error signal is compared
with the internal oscillator sawtooth waveform to generate the
duty cycle waveform. As the control current increases, the duty
cycle decreases. A clock signal from the oscillator sets a latch
which turns on the output MOSFET. The pulse width modulator
resets the latch, turning off the output MOSFET. Note that a
minimum current must be driven into the CONTROL pin
before the duty cycle begins to change.

The maximum duty cycle, DC

MAX,

is set at a default maximum
value of 78% (typical). However, by connecting the LINE­SENSE or MULTI-FUNCTION pin (depending on the package)
to the rectified DC high voltage bus through a resistor with
appropriate value, the maximum duty cycle can be made to
decrease from 78% to 38% (typical) as shown in Figure 11 when
input line voltage increases (see line feed forward with DC

MAX

reduction).

Light Load Frequency Reduction

The pulse width modulator duty cycle reduces as the load at the
power supply output decreases. This reduction in duty cycle is
proportional to the current flowing into the CONTROL pin. As
the CONTROL pin current increases, the duty cycle decreases
linearly towards a duty cycle of 10%. Below 10% duty cycle, to
maintain high efficiency at light loads, the frequency is also
reduced linearly until a minimum frequency is reached at a duty

cycle of 0% (refer to Figure 7). The minimum frequency is
typically 30 kHz and 15 kHz for 132 kHz and 66 kHz operation,
respectively.

This feature allows a power supply to operate at lower frequency
at light loads thus lowering the switching losses while
maintaining good cross regulation performance and low output
ripple.

Error Amplifier

The shunt regulator can also perform the function of an error
amplifier in primary side feedback applications. The shunt
regulator voltage is accurately derived from a temperature­compensated bandgap reference. The gain of the error amplifier
is set by the CONTROL pin dynamic impedance. The
CONTROL pin clamps external circuit signals to the V

C

voltage level. The CONTROL pin current in excess of the
supply current is separated by the shunt regulator and flows
through RE as a voltage error signal.

On-chip Current Limit with External Programmability

The cycle-by-cycle peak drain current limit circuit uses the
output MOSFET ON-resistance as a sense resistor. A current
limit comparator compares the output MOSFET on-state drain
to source voltage, V

DS(ON)

with a threshold voltage. High drain

current causes V

DS(ON)

to exceed the threshold voltage and turns
the output MOSFET off until the start of the next clock cycle.
The current limit comparator threshold voltage is temperature
compensated to minimize the variation of the current limit due
to temperature related changes in R

DS(ON)

of the output MOSFET.
The default current limit of TOPSwitch-GX is preset internally.
However, with a resistor connected between EXTERNAL
CURRENT LIMIT (X) pin (Y or R package) or MULTI­FUNCTION (M) pin (P or G package) and SOURCE pin,
current limit can be programmed externally to a lower level
between 30% and 100% of the default current limit. Please
refer to the graphs in the typical performance characteristics
section for the selection of the resistor value. By setting current
limit low, a larger TOPSwitch-GX than necessary for the power
required can be used to take advantage of the lower R

DS(ON)

for

higher efficiency/smaller heat sinking requirements. With a

PI-2550-092499

128 kHz

4 ms

Time

Switching

Frequency

V

DRAIN

136 kHz

TOP242-249

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Figure 10. Synchronization Timing Diagram.

PI-2637-060600

Oscillator

(SAW)

D

MAX

Enable from

X, L or M Pin (STOP)

Time

second resistor connected between the EXTERNAL CURRENT
LIMIT (X) pin (Y or R package) or MULTI-FUNCTION (M)
pin (P or G package) and the rectified DC high voltage bus, the
current limit is reduced with increasing line voltage, allowing
a true power limiting operation against line variation to be
implemented. When using an RCD clamp, this power limiting
technique reduces maximum clamp voltage at high line. This
allows for higher reflected voltage designs as well as reducing
clamp dissipation.

The leading edge blanking circuit inhibits the current limit
comparator for a short time after the output MOSFET is turned
on. The leading edge blanking time has been set so that, if a
power supply is designed properly, current spikes caused by
primary-side capacitances and secondary-side rectifier reverse
recovery time should not cause premature termination of the
switching pulse.

The current limit is lower for a short period after the leading
edge blanking time as shown in Figure 52. This is due to
dynamic characteristics of the MOSFET. To avoid triggering
the current limit in normal operation, the drain current waveform
should stay within the envelope shown.

Line Under-Voltage Detection (UV)

At power up, UV keeps TOPSwitch-GX off until the input line
voltage reaches the under voltage threshold. At power down,
UV prevents auto-restart attempts after the output goes out of
regulation. This eliminates power down glitches caused by the
slow discharge of large input storage capacitor present in
applications such as standby supplies. A single resistor connected
from the LINE-SENSE pin (Y or R package) or MULTI­FUNCTION pin (P or G package) to the rectified DC high
voltage bus sets UV threshold during power up. Once the power
supply is successfully turned on, the UV threshold is lowered to

40% of the initial UV threshold to allow extended input voltage
operating range (UV low threshold). If the UV low threshold
is reached during operation without the power supply losing
regulation the device will turn off and stay off until UV (high
threshold) has been reached again. If the power supply loses
regulation before reaching the UV low threshold, the device
will enter auto-restart. At the end of each auto-restart cycle (S7),
the UV comparator is enabled. If the UV high threshold is not
exceeded the MOSFET will be disabled during the next cycle (see
figure 8). The UV feature can be disabled independent of OV
feature as shown in Figure 19 and 23.

Line Overvoltage Shutdown (OV)

The same resistor used for UV also sets an overvoltage threshold
which, once exceeded, will force TOPSwitch-GX output into
off-state. The ratio of OV and UV thresholds is preset at 4.5 as
can be seen in Figure 11. When the MOSFET is off, the rectified
DC high voltage surge capability is increased to the voltage
rating of the MOSFET (700 V), due to the absence of the
reflected voltage and leakage spikes on the drain. A small
amount of hysteresis is provided on the OV threshold to prevent
noise triggering. The OV feature can be disabled independent
of the UV feature as shown in Figure 18 and 32.

Line Feed Forward with DC

MAX

Reduction

The same resistor used for UV and OV also implements line
voltage feed forward which minimizes output line ripple and
reduces power supply output sensitivity to line transients. This
feed forward operation is illustrated in Figure 7 by the different
values of IL (Y or R package) or IM (P or G Package). Note that
for the same CONTROL pin current, higher line voltage results
in smaller operating duty cycle. As an added feature, the
maximum duty cycle DC

MAX

is also reduced from 78% (typical)
at a voltage slightly higher than the UV threshold to 38%
(typical) at the OV threshold (see Figures 7, 11). Limiting

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DC

MAX

at higher line voltages helps prevent transformer
saturation due to large load transients in forward converter
applications. DC

MAX

of 38% at the OV threshold was chosen to
ensure that the power capability of the TOPSwitch-GX is not
restricted by this feature under normal operation.

Remote ON/OFF and Synchronization

TOPSwitch-GX can be turned on or off by controlling the
current into the LINE-SENSE pin or out from the EXTERNAL
CURRENT LIMIT pin (Y or R package) and into or out from
the MULTI-FUNCTION pin (P or G package) (see Figure 11).
In addition, the LINE-SENSE pin has a 1 V threshold comparator
connected at its input. This voltage threshold can also be used
to perform remote ON/OFF control. This allows easy
implementation of remote ON/OFF control of TOPSwitch-GX
in several different ways. A transistor or an optocoupler output
connected between the EXTERNAL CURRENT LIMIT or
LINE-SENSE pins (Y or R package) or the MULTI-FUNCTION
pin (P or G package) and the SOURCE pin implements this
function with “active-on” (Figure 22, 29 and 36) while a
transistor or an optocoupler output connected between the
LINE-SENSE pin (Y or R package) or the MULTI-FUNCTION
(P or G package) pin and the CONTROL pin implements the
function with “active-off” (Figure 23 and 37).

When a signal is received at the LINE-SENSE pin or the
EXTERNAL CURRENT LIMIT pin (Y or R package) or the
MULTI-FUNCTION pin (P or G package) to disable the output
through any of the pin functions such as OV, UV and remote
ON/OFF, TOPSwitch-GX always completes its current switching
cycle, as illustrated in Figure 10, before the output is forced off.
The internal oscillator is stopped slightly before the end of the
current cycle and stays there as long as the disable signal exists.
When the signal at the above pins changes state from disable to
enable, the internal oscillator starts the next switching cycle.
This approach allows the use of this pin to synchronize
TOPSwitch-GX to any external signal with a frequency lower
than its internal switching frequency.

As seen above, the remote ON/OFF feature allows the
TOPSwitch-GX to be turned on and off instantly, on a cycle-by­cycle basis, with very little delay. However, remote ON/OFF
can also be used as a standby or power switch to turn off the
TOPSwitch-GX and keep it in a very low power consumption
state for indefinitely long periods. If the TOPSwitch-GX is held
in remote off state for long enough time to allow the CONTROL
pin to dishcharge to the internal supply under-voltage threshold
of 4.8 V (approximately 32 ms for a 47 µF CONTROL pin
capacitance), the CONTROL pin goes into the hysteretic mode
of regulation. In this mode, the CONTROL pin goes through
alternate charge and discharge cycles between 4.8 V and 5.8 V
(see CONTROL pin operation section above) and runs entirely
off the high voltage DC input, but with very low power
consumption (160 mW typical at 230 VAC with M or X pins

open). When the TOPSwitch-GX is remotely turned on after
entering this mode, it will initiate a normal start-up sequence
with soft-start the next time the CONTROL pin reaches 5.8 V.
In the worst case, the delay from remote on to start-up can be
equal to the full discharge/charge cycle time of the CONTROL
pin, which is approximately 125 ms for a 47 µF CONTROL pin
capacitor. This reduced consumption remote off mode can
eliminate expensive and unreliable in-line mechanical switches.
It also allows for microprocessor controlled turn-on and turn­off sequences that may be required in certain applications such
as inkjet and laser printers.

Soft-Start

Two on-chip soft-start functions are activated at start-up with a
duration of 10 ms (typical). Maximum duty cycle starts from
0% and linearly increases to the default maximum of 78% at the
end of the 10 ms duration and the current limit starts from about
85% and linearly increases to 100% at the end of the 10ms
duration. In addition to start-up, soft-start is also activated at
each restart attempt during auto-restart and when restarting
after being in hysteretic regulation of CONTROL pin voltage
(V

C

), due to remote off or thermal shutdown conditions. This
effectively minimizes current and voltage stresses on the output
MOSFET, the clamp circuit and the output rectifier during start­up. This feature also helps minimize output overshoot and
prevents saturation of the transformer during start-up.

Shutdown/Auto-Restart

To minimize TOPSwitch-GX power dissipation under fault
conditions, the shutdown/auto-restart circuit turns the power
supply on and off at an auto-restart duty cycle of typically 4%
if an out of regulation condition persists. Loss of regulation
interrupts the external current into the CONTROL pin. V

C

regulation changes from shunt mode to the hysteretic auto­restart mode as described in CONTROL pin operation section.
When the fault condition is removed, the power supply output
becomes regulated, VC regulation returns to shunt mode, and
normal operation of the power supply resumes.

Hysteretic Over-Temperature Protection

Temperature protection is provided by a precision analog
circuit that turns the output MOSFET off when the junction
temperature exceeds the thermal shutdown temperature
(140 °C typical). When the junction temperature cools to below
the hysteretic temperature, normal operation resumes providing
automatic recovery. A large hysteresis of 70 °C (typical) is
provided to prevent overheating of the PC board due to a
continuous fault condition. VC is regulated in hysteretic mode
and a 4.8 V to 5.8 V (typical) sawtooth waveform is present on
the CONTROL pin while in thermal shutdown.

Bandgap Reference

All critical TOPSwitch-GX internal voltages are derived from a
temperature-compensated bandgap reference. This reference is

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also used to generate a temperature-compensated current
reference which is trimmed to accurately set the switching
frequency, MOSFET gate drive current, current limit, and the
line OV/UV thresholds. TOPSwitch-GX has improved circuitry
to maintain all of the above critical parameters within very tight
absolute and temperature tolerances.

High-Voltage Bias Current Source

This current source biases TOPSwitch-GX from the DRAIN pin
and charges the CONTROL pin external capacitance during
start-up or hysteretic operation. Hysteretic operation occurs
during auto-restart, remote off and over-temperature shutdown.
In this mode of operation, the current source is switched on and
off with an effective duty cycle of approximately 35%. This
duty cycle is determined by the ratio of CONTROL pin charge
(I

C

) and discharge currents (I

CD1

and I

CD2

). This current source
is turned off during normal operation when the output MOSFET
is switching. The effect of the current source switching will be
seen on the DRAIN voltage waveform as small disturbances
and is normal.

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Refer to Table 2 for possible combinations of the functions with
example circuits shown in Figure 16 through Figure 40. A
description of specific functions in terms of the LINE-SENSE
pin I/V characteristic is shown in Figure 11 (right hand side).
The horizontal axis represents LINE-SENSE pin current with
positive polarity indicating currents flowing into the pin. The
meaning of the vertical axes varies with functions. For those
that control the on/off states of the output such as UV, OV and
remote ON/OFF, the vertical axis represents the enable/disable
states of the output. UV triggers at IUV (+50 µA typical with
30 µA hysteresis) and OV triggers at IOV (+225 µA typical with
8 µA hysteresis). Between the UV and OV thresholds, the
output is enabled. For line feed forward with DC

MAX

reduction,

the vertical axis represents the magnitude of the DC

MAX

. Line

feed forward with DC

MAX

reduction lowers maximum duty cycle

from 78% at I

L(DC)

(+60 µA typical) to 38% at IOV (+225 µA).

EXTERNAL CURRENT LIMIT (X) Pin Operation
(Y and R Packages)

When current is drawn out of the EXTERNAL CURRENT
LIMIT pin, it works as a voltage source of approximately 1.3
V up to a maximum current of –240 µA (typical). At –240 µA,
it turns into a constant current source (refer to Figure 12a).

There are two functions available through the use of the
EXTERNAL CURRENT LIMIT pin: external current limit
and remote ON/OFF. Connecting the EXTERNAL CURRENT
LIMIT pin and SOURCE pin disables the two functions. In
high efficiency applications this pin can be used to reduce the
current limit externally to a value close to the operating peak
current, by connecting the pin to the SOURCE pin through a
resistor. The pin can also be used as a remote on/off. Table 2
shows several possible combinations using this pin. See Figure

FREQUENCY (F) Pin Operation

The FREQUENCY pin is a digital input pin available in the
Y or R package only. Shorting the FREQUENCY pin to
SOURCE pin selects the nominal switching frequency of
132 kHz (Figure 13) which is suited for most applications. For
other cases that may benefit from lower switching frequency
such as noise sensitive video applications, a 66 kHz switching
frequency (half frequency) can be selected by shorting the
FREQUENCY pin to the CONTROL pin (Figure 14). In
addition, an example circuit shown in Figure 15 may be used to
lower the switching frequency from 132 kHz in normal
operation to 66 kHz in standby mode for very low standby
power consumption.

LINE-SENSE (L) Pin Operation (Y and R Packages)

When current is fed into the LINE-SENSE pin, it works as a
voltage source of approximately 2.6 V up to a maximum
current of +400 µA (typical). At +400 µA, this pin turns into
a constant current sink. Refer to Figure 12a. In addition, a
comparator with a threshold of 1 V is connected at the pin and
is used to detect when the pin is shorted to the SOURCE pin.

There are a total of four functions available through the use of
the LINE-SENSE pin: OV, UV, line feed forward with DC

MAX

reduction, and remote ON/OFF. Connecting the LINE-SENSE
pin to the SOURCE pin disables all four functions. The LINE­SENSE pin is typically used for line sensing by connecting a
resistor from this pin to the rectified DC high voltage bus to
implement OV, UV and DC

MAX

reduction with line voltage. In
this mode, the value of the resistor determines the line OV/UV
thresholds, and the DC

MAX

is reduced linearly with rectified DC
high voltage starting from just above the UV threshold. The pin
can also be used as a remote on/off and a synchronization input.

Using Feature Pins

✔

✔✔ ✔ ✔ ✔

✔✔ ✔✔✔

✔✔✔✔

✔

✔✔ ✔✔ ✔✔

✔✔✔✔✔✔ ✔

16 17 18 19 20 21 22 23 24 25 26 27 28 29

Table 2. Typical LINE-SENSE and EXTERNAL CURRENT LIMIT Pin Configurations.

LINE-SENSE AND EXTERNAL CURRENT LIMIT PIN TABLE*

*This table is only a partial list of many LINE-SENSE and EXTERNAL CURRENT LIMIT pin configurations that are possible.

▲

Figure Number
Three Terminal Operation

Under-Voltage
Overvoltage
Line Feed Forward (DC

MAX

)
Overload Power Limiting
External Current Limit
Remote ON/OFF

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✔

✔✔ ✔

✔✔ ✔

✔✔

✔

✔✔ ✔✔

✔✔✔✔✔

Table 3. Typical MULTI-FUNCTION Pin Configurations.

MULTI-FUNCTION PIN TABLE*

30 31 32 33 34 35 36 37 38 39 40

*This table is only a partial list of many MULTI-FUNCTION pin configurations that are possible.

▲

Figure Number
Three Terminal Operation

Under-Voltage
Overvoltage
Line Feed Forward (DC

MAX

)
Overload Power Limiting
External Current Limit
Remote ON/OFF

11 for a description of the functions where the horizontal axis
(left hand side) represents the EXTERNAL CURRENT LIMIT
pin current. The meaning of the vertical axes varies with
function. For those that control the on/off states of the output
such as remote ON/OFF, the vertical axis represents the enable/
disable states of the output. For external current limit, the
vertical axis represents the magnitude of the I

LIMIT

. Please see
graphs in the typical performance characteristics section for the
current limit programming range and the selection of appropriate
resistor value.

MULTI-FUNCTION (M) Pin Operation (P and G Packages)

The LINE-SENSE and EXTERNAL CURRENT LIMIT pin
functions are combined to a single MULTI-FUNCTION pin for
P and G packages. The comparator with a 1 V threshold at the
LINE-SENSE pin is removed in this case as shown in Figure 2b.
All of the other functions are kept intact. However, since some
of the functions require opposite polarity of input current
(MULTI-FUNCTION pin), they are mutually exclusive. For
example, line sensing features cannot be used simultaneously
with external current limit setting. When current is fed into the
MULTI-FUNCTION pin, it works as a voltage source of
approximately 2.6 V up to a maximum current of +400 µA
(typical). At +400 µA, this pin turns into a constant current sink.
When current is drawn out of the MULTI-FUNCTION pin, it
works as a voltage source of approximately 1.3 V up to a
maximum current of –240 µA (typical). At –240 µA, it turns
into a constant current source. Refer to Figure 12b.

There are a total of five functions available through the use of
the MULTI-FUNCTION pin: OV, UV, line feed forward with
DC

MAX

reduction, external current limit and remote ON/OFF. A
short circuit between the MULTI-FUNCTION pin and
SOURCE pin disables all five functions and forces

TOPSwitch-GX to operate in a simple three terminal mode like
TOPSwitch-II. The MULTI-FUNCTION pin is typically used

for line sensing by connecting a resistor from this pin to the
rectified DC high voltage bus to implement OV, UV and DC

MAX

reduction with line voltage. In this mode, the value of the
resistor determines the line OV/UV thresholds, and the DC

MAX

is reduced linearly with rectified DC high voltage starting from
just above the UV threshold. In high efficiency applications
this pin can be used in the external current limit mode instead,
to reduce the current limit externally to a value close to the
operating peak current, by connecting the pin to the SOURCE
pin through a resistor. The same pin can also be used as a remote
on/off and a synchronization input in both modes. Please refer
to Table 3 for possible combinations of the functions with
example circuits shown in Figure 30 through Figure 40. A
description of specific functions in terms of the MULTI­FUNCTION pin I/V characteristic is shown in Figure 11. The
horizontal axis represents MULTI-FUNCTION pin current
with positive polarity indicating currents flowing into the pin.
The meaning of the vertical axes varies with functions. For
those that control the on/off states of the output such as UV, OV
and remote ON/OFF, the vertical axis represents the enable/
disable states of the output. UV triggers at IUV (+50 µA typical)
and OV triggers at IOV (+225 µA typical with 30 µA hysteresis).
Between the UV and OV thresholds, the output is enabled. For
external current limit and line feed forward with DC

MAX

reduction, the vertical axis represents the magnitude of the I

LIMIT

and DC

MAX

. Line feed forward with DC

MAX

reduction lowers

maximum duty cycle from 78% at I

M(DC)

(+60 µA typical) to 38%

at IOV (+225 µA). External current limit is available only with
negative MULTI-FUNCTION pin current. Please see graphs in
the typical performance characteristics section for the current
limit programming range and the selection of appropriate resistor
value.

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Figure 11. MULTI-FUNCTION (P or G package), LINE-SENSE, and EXTERNAL CURRENT LIMIT (Y or R package) Pin Characteristics.

-250 -200 -150 -100 -50 0 50 100 150 200 250 300 350 400

PI-2636-040501

Output
MOSFET
Switching

(Enabled)

(Disabled)

I

LIMIT

(Default)

DC

MAX

(78.5%)

Current

Limit

M Pin

L PinX Pin

Maximum

Duty Cycle

V

BG

-22 µA

-27 µA
V

BG

+ V

TP

I

I

I

I

I

UV

I

REM(N)

I

OV

Pin Voltage

Note: This figure provides idealized functional characteristics with typical performance values. Please refer to the parametric
table and typical performance characteristics sections of the data sheet for measured data.

X and L Pins (Y or R Package) and M Pin (P or G Package) Current (µA)

Disabled when supply
output goes out of
regulation

TOP242-249

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Figure 12a. LINE-SENSE (L), and EXTERNAL CURRENT LIMIT (X) Pin Input Simplified Schematic.

Figure 12b. MULTI-FUNCTION (M) Pin Input Simplified Schematic.

VBG + V

T

1 V

V

BG

240 µA

400 µA

CONTROL Pin

Y and R Package

(Voltage Sense)

(Positive Current Sense - Under-Voltage,

Overvoltage, ON/OFF Maximum Duty

Cycle Reduction)

(Negative Current Sense - ON/OFF,

Current Limit Adjustment)

PI-2634-033001

TOPSwitch-GX

LINE-SENSE (L)

EXTERNAL CURRENT LIMIT (X)

VBG + V

T

V

BG

240 µA

400 µA

CONTROL Pin

MULTI-FUNCTION (M)

(Positive Current Sense - Under-Voltage,

Overvoltage, Maximum Duty

Cycle Reduction)

(Negative Current Sense - ON/OFF,

Current Limit Adjustment)

PI-2548-092399

TOPSwitch-GX

P and G Package

TOP242-249

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Figure 15. Half Frequency Standby Mode (For High Standby

Efficiency).

Figure 13. Full Frequency Operation (132 kHz). Figure 14. Half Frequency Operation (66 kHz).

Typical Uses of FREQUENCY (F) Pin

PI-2654-071700

DC

Input

Voltage

+

-

D

S

C

CONTROL

F

PI-2655-071700

DC

Input

Voltage

+

-

D

S

C

CONTROL

F

PI-2656-040501

DC

Input

Voltage

+

-

D

S

C

STANDBY

QS can be an optocoupler output.

CONTROL

F

20 kΩ

R

HF

1 nF

Q

S

47 kΩ