www.fairchildsemi.com

FOD41xx and FOD42xx

Fairchild’s New 600V and 800V Zero Crossing

and Random Phase Snubberless Triac Driver

Optocouplers

2

These devices represent a new addition to Fairchild’s broad

TRIAC driver optocoupler portfolio. They compliment our

existing portfolio of monolithic TRIAC driver optocouplers

(MOC3xxxM and FODM3xxx). They are the best-in-class

TRIAC driver optocouplers in the market.

Snubberless TRIAC Driver Optocouplers

3

Answer – The power TRIAC and the optocoupler that drives it

almost always require an RC network to improve the

optocoupler’s static and commutating dv/dt. This network

eliminates the false firing of the optocoupler TRIAC driver

when driving inductive loads. This RC circuit is referred to as

a “snubber circuit”.

“What‟s a Snubberless TRIAC Drive Optocoupler”?

Snubber circuit

Triac drive

optocoupler

Discrete power

triac

4

The existing TRIAC driver families in our portfolio (MOC3xxxM

and FODM30xx) are called monolithic TRIAC drivers. The

reason is both SCR’s that form the TRIAC function are

integrated onto a single silicon photodetector chip. This is

good for compact assembly but bad for commutating dv/dt

performance due to shared charge stored in the substrate

common to the two integrated SCRs (refer to Figure 9

AN3008). The FOD4xx has two separate SCR chips which

eliminates leakage of substrate current between the forward

and reverse biased SCRs during operation. This greatly

improves commutating dv/dt.

Hybrid vs Monolithic TRIAC Driver Optocoupler

5

Snubberless TRIAC Driver Optocouplers

Value Proposition:

The value proposition for these products is key to selling

them. Since these parts are roughly 3x to 4x more expensive

than the MOC30xxM and FODM30xx optocouplers, customers

need to understand why these devices should be considered.

• Superior commutating and static dv/dt performance eliminates

expensive snubber capacitor

• Low input drive current saves on power consumption

• Elimination of R-C snubber reduces standby power consumption

• Only random phase TRIAC driver optocoupler capable of

blocking 800V (600V is best in class for

monolithic solutions)

6

Due to the FOD4xx’s high commutating and static dv/dt

immunity (10kV/us minimum), its performance is such that

additional noise filtering is not required. This allows the

snubber across the TRIAC driver to be eliminated from the

circuit. Since the snubber capacitor is across the mains, it

must be safety certified. These special safety certified

capacitors are very expensive, approximately $0.35 each in

high volume! Those capacitors are also about four times the

size of the optocoupler which makes removing them a

significant space savings!

Value Proposition – Reduced Component Count

7

Aside from the cost savings of removing the RC snubber

components, there’s another advantage. Selecting the values

of the RC network is tedious. Often, designers don’t know the

power factor of their load, what noise will come from the

mains, the type of load being switched, or even what type of

load will be connected to the circuit (e.g., in the case of

hockey puck solid state relays). As a result, they are forced to

estimate the values and then hand tune the circuit on the

bench. For the case of the SSR, that’s impossible because

they can’t simulate an undefined load. The FOD4xx eliminates

this hassle by removing those components from the circuit.

Value Proposition – Ease of Design

8

Value Proposition – High dv/dt Immunity

• The FOD4xx TRIAC driver offers a static and

commutating dv/dt noise rejection in excess of 10kV/μs

@ 800V peak.

• This exceptional performance is possible because these

ICs incorporate an active dv/dt clamp. When a fast

transient is present on the power mains and the LED is

turned off, the dv/dt clamp circuit disables the TRIAC

driver’s trigger circuit, thus eliminating false triggering.

9

The FOD420x and FOD410x devices have a maximum IFT

rating of 2mA while the FOD421x and FOD411x devices have a

maximum IFT rating of 1.3mA. This compares to 5mA or higher

maximum ratings for monolithic triacs. The low IFT rating of

the FOD4xx devices allows designers to significantly reduce

the current supplied to the optocoupler’s LED resulting in a

significant power savings. It also allows for the removal of the

buffer from the input circuit since the 2mA drive current is

within the drive capability of CMOS gates.

Value Proposition – Low Input Drive Current

10

By eliminating the snubber network a significant reduction in

standby power consumption can be realized. The snubber

circuit consumes power even when the load is in the off-state.

As an example, a 240V AC Mains application using a 0.1uF

snubber capacitor conducts 10mA in the off-state translating

to a power loss of 2W. With new directives for reducing

standby power as energy costs skyrocket, the power savings

offered by these devices can substantially help designers

achieve their standby power targets.

Value Proposition – Reduced Standby Power

11

The FOD4208 and FOD4218 are rated for a blocking voltage of

800V minimum while the equivalent monolithic devices are

limited to a 600V rating. The 800V rating is important for high

mains voltage applications like those found in Europe which

have a peak to peak voltage of 480V. In these applications, the

600V devices often don’t allow enough margin for noise,

resulting in random device failures in the application. The

solution for those devices is to tie two optocouplers together

along with a balancing network to ensure both triacs turn on

at the same time (see AN-3003, figure 7). This is an expensive

and board space consuming solution. With a typical blocking

voltage of 1000V, a single FOD42X8 offers a sufficient noise

margin for these applications.

Value Proposition – High Blocking Voltage

12

The FOD4xx optocouplers go into the same applications as

the monolithic triac drive optocouplers. These devices are

often used when customers cannot resolve application

problems and need to upgrade to a higher performance opto

driver.

Applications include:

• Solid-state relays

• Consumer appliances (vacuum cleaners, washing machines, etc)

• Industrial controls

Applications – Where to Sell These Products

13

Product Overview

• New snubberless triac Drive optocouplers:

• High static and commutating dv/dt immunity

(10kV/us)

• High blocking voltage (VDM)

• FOD420/4216/410/4116 – 600V minimum

• FOD4208/4218/4108/4118 – 800V minimum

• Low input drive current (IFT):

• FOD420/4208/410/4108 – 2mA maximum

• FOD4216/4218/4116/4118 – 1.3mA

maximum

• 5000V isolation voltage rating

• High current sink capability:

• 300mA maximum (continuous)

• 3A maximum (peak, non repetitive)

FOD42XX

14

Key Specifications – Random Phase

* Note – The maximum IFT is the highest LED current required to

guarantee the device will switch to the „on‟ state. When designing in the

part, it is therefore recommended that an additional 25% to 50% be

added to the maximum current rating spec to compensate for

temperature and time degradation of the LED.

Part Number VTM

(V)

Max

IH(µA)

Max

VDM

(V)

Min

dv/dt(V/µs)

Min

VISO

AC (RMS)Min

FOD420 2 3 500 600 10,000 5kV

FOD4208 2 3 500 800 10,000 5kV

FOD4216 1.3 3 500 600 10,000 5kV

FOD4218 1.3 3 500 800 10,000 5kV

IFT

(mA)

Max*

15

Key Specifications – Zero Cross

* Note – The maximum IFT is the highest LED current required to

guarantee the device will switch to the „on‟ state. When designing in the

part, it is therefore recommended that an additional 25% to 50% be

added to the maximum current rating spec to compensate for

temperature and time degradation of the LED.

Part Number VTM

(V)

Max

VINH

(V)

Max

VDM

(V)

Min

dv/dt(V/µs)

Min

VISO

AC (RMS)Min

FOD410 2 3 25 600 10,000 5kV

FOD4108 2 3 25 800 10,000 5kV

FOD4116 1.3 3 25 600 10,000 5kV

FOD4118 1.3 3 25 800 10,000 5kV

IFT

(mA)

Max*

16

Discrete Power TRIACS

Fairchild’s discrete power TRIACs can be sold in conjunction with

these optocouplers. TRIAC drive optocouplers are not designed to

directly drive a load. They are designed to drive a power TRIAC.

Therefore, you should always find a power TRIAC accompanying the

opto driver in application. Be sure to promote our discrete power

TRIACs to add Fairchild content to your design wins. Recommended

power TRIAC part numbers are as follows:

• FKN08PN60S (600V, TO-92 package)

• FKPF8N80 (800V, TO-200F package)

Other vendors do make snubberless power TRIACs. These devices

allow the customer to remove the snubber RC from both the opto

driver and the power TRIAC. Otherwise the power TRIAC

would still need a snubber.

17

Packaging

You may be asking why this part is housed in a black package

being that most of our 6-pin DIP products are moving to the

white package. The reason is due to the large die size for the

SCRs. Since there are two of them in the package, more real

estate is needed to fit them in the package. By using a double

molded (over-under) construction, it moves the LED above the

photodetector which leaves more space for the detector

chips. The double molded package also meets the 260°C

reflow requirement for Pb free assembly since the inner clear

material is a hard epoxy as opposed to the soft gel material

found in our other 6-pin DIP packages.

18

Packaging

Example X-Ray of over-under Example X-Ray of white

Construction coplanar construction

19

Safety Agency Certification

• UL approved to standard

UL1577

• VDE approved to standard

EN60747-5-2

• NEMKO approved to standard

IEC60950-1:2001