TOP221 データシートの表示（PDF） - Power Integrations, Inc

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TOP221

Three-Terminal Off-Line PWM Switch

Power Integrations, Inc 

TOP221-227

Key Application Considerations

General Guidelines

• Keep the SOURCE pin length very short. Use a Kelvin

connection to the SOURCE pin for the CONTROL pin by-

pass capacitor. Use single point grounding techniques

at the SOURCE pin as shown in Figure 9.

• Minimize peak voltage and ringing on the DRAIN volt-

age at turn-off. Use a Zener or TVS Zener diode to

clamp the drain voltage below the breakdown voltage

rating of TOPSwitch under all conditions, including start-

up and overload. The maximum recommended clamp

Zener voltage for the TOP2XX series is 200 V and the

corresponding maximum reflected output voltage on the

primary is 135 V. Please see Step 4: AN-16 in the 1996-

97 Data Book and Design Guide or on our Web site.

• The transformer should be designed such that the rate

of change of drain current due to transformer saturation

is within the absolute maximum specification (∆ID in

100 ns before turn off as shown in Figure 13). As a

guideline, for most common transformer cores, this can

be achieved by maintaining the Peak Flux Density (at

maximum ILIMIT current) below 4200 Gauss (420 mT).

The transformer spreadsheets Rev. 2.1 (or later) for con-

tinuous and Rev.1.0 (or later) for discontinuous conduc-

tion mode provide the necessary information.

• Do not plug TOPSwitch into a “hot” IC socket dur-

ing test. External CONTROL pin capacitance may be

charged to excessive voltage and cause TOPSwitch

damage.

• While performing TOPSwitch device tests, do not

exceed maximum CONTROL pin voltage of 9 V or maxi-

mum CONTROL pin current of 100 mA.

• Under some conditions, externally provided bias or

supply current driven into the CONTROL pin can hold

the TOPSwitch in one of the 8 auto-restart cycles in-

definitely and prevent starting. To avoid this problem when

doing bench evaluations, it is recommended that the VC

power supply be turned on before the DRAIN voltage is

applied. TOPSwitch can also be reset by shorting the

CONTROL pin to the SOURCE pin momentarily.

• CONTROL pin currents during auto-restart operation

are much lower at low input voltages (< 36 V) which in-

creases the auto-restart cycle time (see the IC vs. DRAIN

Voltage Characteristic curve).

• Short interruptions of AC power may cause TOPSwitch

to enter the 8-count auto-restart cycle before starting

again. This is because the input energy storage capaci-

tors are not completely discharged and the CONTROL

pin capacitance has not discharged below the internal

power-up reset voltage.

• In some cases, minimum loading may be necessary to

keep a lightly loaded or unloaded output voltage within

the desired range due to the minimum ON-time.

Replacing TOPSwitch with TOPSwitch-II

There is no external latching shutdown function in

TOPSwitch-II. Otherwise, the functionality of the TOPSwitch-II

devices is same as that of the TOPSwitch family. However,

before considering TOPSwitch-II as a 'drop in' replace-

ment in an existing TOPSwitch design, the design should

be verified as described below.

The new TOPSwitch-II family offers more power capability

than the original TOPSwitch family for the same MOSFET

RDS(ON). Therefore, the original TOPSwitch design must

be reviewed to make sure that the selected TOPSwitch-II

replacement device and other primary components are not

over stressed under abnormal conditions.

The following verification steps are recommended:

• Check the transformer design to make sure that it

meets the ∆ID specification as outlined in the General

Guidelines section above.

• Thermal: Higher power capability of the TOPSwitch-II

would in many instances allow use of a smaller MOS-

FET device (higher RDS(ON)) for reduced cost. This may

affect TOPSwitch power dissipation and power supply

efficiency. Therefore thermal performance of the power

supply must be verified with the selected TOPSwitch-II

device.

• Clamp Voltage: Reflected and Clamp voltages should

be verified not to exceed recommended maximums

for the TOP2XX Series: 135 V Reflected/200 V Clamp.

Please see Step 4: AN-16 in the Data Book and Design

Guide and readme.txt file attached to the transformer

design spreadsheets.

• Agency Approval: Migrating to TOPSwitch-II may

require agency re-approval.

8

Rev. G 08/16

www.power.com

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