TNY287 questions

2 posts / 0 new

Hello
Please could you answer the following questions about TNY287?
If the current into the EN/UV pin is less than 2uA then TNY287 does
not operate the line undervoltage function?
If the current into the EN/UV pin is >2uA but less then 25uA then the
TNY287 goes into line undervoltage shutdown?
If the current into the EN/UV pin is > 25uA, then the TNY287 does not
go into undervoltage shutdown?
If the TNY287 is being supplied through the DRAIN pin, then its BP/M pin
will be 5.85V?
If the TNY287 is being supplied from its bias winding, (via a resistor), then
its BP/M voltage will be 6.4V?
If i want to monitor the temperature of the TNY287 with a thermocouple, then is the best place
to glue the thermopcouple on the plastic case, near the SOURCE pins?
What woudl be the maximum allowable temperature on the plastic case of the TNY287, for long life
operation. (The datasheet refers to 110degC, but says that this is on the source pins.....but as you
know, we cannot place a thermocouple on the SOURCE pins as they are metal.

Hi treez,

Thank you for using power integrations product.
To help you out , can you please provide some information on your design?

It would be helpful to provide the following,

* Output voltage and current
* Input voltage
* Schematic
* Transformer design

To answer your questions:

1) If the current into the EN/UV pin is >2uA but less then 25uA then the
TNY287 goes into line undervoltage shutdown?

* The EN/UV pin senses line undervoltage conditions through an external resistor connected to the DC line voltage. If there is no external resistor connected to this pin,
TinySwitch-4 detects its absence (Iuv < 2 μA), and disables the line undervoltage function.

* it is best to provide the schematic.
A UV function is also possible with an external resistor connected to the BP/UV pin,
when the UV/EN pin current is below Iuv - reset hysteresis (Typ 18.75uA) then a shutdown function is provided.

2) If the current into the EN/UV pin is > 25uA, then the TNY287 does not
go into undervoltage shutdown?

* MOSFET switching is enabled after EN/UV pin current (Iuv) exceeds 25 μA.
Since it is switching then its not UV

3) If the TNY287 is being supplied through the DRAIN pin, then its BP/M pin
will be 5.85V?

* Yes, The 5.85 V regulator charges the bypass capacitor connected to the
BP pin to 5.85 V by drawing a current from the voltage on the
DRAIN pin whenever the MOSFET is off.

4) If the TNY287 is being supplied from its bias winding, (via a resistor), then
its BP/M voltage will be 6.4V?

* The purpose of the bias winding in combination of a zener diode is to provide an output OVP
protection and to decrease no load consumption. Typically 15-30V bias winding voltage is good . There is an internal 6.4V shunt regulator that clamps the PB/M pin to 6.4V. So for typical OVP the zener voltage rating should be higher than 6.4V + Vbias.

5) If i want to monitor the temperature of the TNY287 with a thermocouple, then is the best place
to glue the thermopcouple on the plastic case, near the SOURCE pins?

* Yes it is recommended to place it on the plastic case near the source pin since the mosfet will
be switching at high frequencies and will be hot

6) What would be the maximum allowable temperature on the plastic case of the TNY287, for long life operation.
* typically a 85% derating is good. The OTP is usually around 142 degrees Celsius,
so it is best that the thermal operating condition for the device is much lower

Hope this helps