Heat Dissipation for HTSSOP TPL 9202 Relay Driver

12 Feb 2011

Mbed Community

I bought a TPL9202 relay driver.

http://focus.tij.co.jp/jp/lit/ds/slis124d/slis124d.pdf

This is a surface mount device.

It is a HTSSOP package.

Fine, no problem

I bought the dip adapter for above chip from SPARKFUN electronics at a bargain price of about 3 pounds 50!

I managed to solder smd chip to dip adapter after a failed attempt.

I managed to power the mbed through the 5V out pin!

I was just about to test the MOSI MISO SCLK pins when the light on my mbed went out.

I am pretty sure that it is because the smd chip overheated.

I felt the chip and it is very hot.

There is a small pad at the bottom of the chip, I think this is referred to as a PWP pad

My question is this.

How do I stop the chip from overheating?

Will a heatsink glued on top be enough?

Exactly what heatsink do I need to buy?

Do I need to attach some kind of heat pad at the bottom?

I live in the uk.

Cheers Dave

13 Feb 2011

1. Most likely, the regulator in the TPL9202 is overheating and shutting down. You are powering the mbed from the TPL9202's 5-volt output. IIRC, the mbed draws about 200mA. (That is right at the spec limit for the TPL9202's output current, BTW). If you are feeding the '9202 from a raw supply of, say, 12 volts, then it is trying to dissipate (12 - 5) Volts * 0.2Amps = 1.4 watts. It is going to get quite hot if the chip doesn't have a good path for the heat to get to thermal vias on the PCB. TI says

Quote:

In a single-layer board application, the thermal pad is attached to a heat spreader (copper areas) by a low thermal-impedance attachment method (solder paste or thermal conductive epoxy). With either method, it is advisable to use as many copper traces as possible to dissipate the heat.

You could try putting a heatsink on top, though the part is designed to conduct heat out the bottom. Rather than go down that path, however, I'd suggest it would be simpler just to provide a separate power supply regulator for the mbed. Something like an LM7805 would work. These are easy to heat sink, not being fiddly surface-mount parts :-)

2. Alternatively, the problem could be that something is awry in your breakout board.

  • Try disconnecting everything from the breakout board except Vin and ground. (No power to the mbed, no SSP signals.) If the chip still gets hot, then look for a short between one of the output pins and Vin or +5. Basically, break out the biggest magnifying glass you can find and examine the HTSSOP solder pads carefully.

Good luck.

Edit: You know, come to think of it the mbed does not need a regulated input anyway. So the simplest approach to case 1 above would be to feed the mbed's Vin through a dropping resistor from the raw supply. That shifts the heat load from a regulator (whether inside the TPL9202 or outboard as suggested above) into something that is designed to handle it: a power resistor.

For example, if the raw supply is +12, you would like to drop around 6 or 7 volts across the resistor that feeds Vin, to end up with 5 - 6 volts at the mbed. At 200mA, that would require 6 V/ 200mA = 30 ohms. A 5-watt power resistor would be a good choice, since it is going to dissipate well over a watt and you don't want to be redlining the temperature.