CPC1580

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2. Introduction

The CPC1580 Isolated Gate Driver uses an efficient

optocoupler design to provide remote gate drive

isolation between the LED control current input and

the MOSFET gate drive output. The CPC1580 is used

in conjunction with a MOSFET transistor for remote

switching of DC loads (Figure 1) and two MOSFETS

and a diode at low-frequency AC rates (Figure 2)

where isolated power is unavailable.

By selecting a few external components, the charge

capacitor and resistors, the designer has control over

the operating parameters of the CPC1580 circuit, and

can customize the circuit to accommodate the

requirements of a wide selection of MOSFETs.

The designer just needs to know the MOSFET total

can be chosen. The capacitance of the storage

3. Functional Description

The CPC1580 is operational when sufficient input

control current is flowing, the LED is turned on, and

the gate current is flowing. The LED illuminates the

photovoltaics (converts light into electrical power, or

photocurrent), which provides current to turn on the

NPN bipolar transistor. The NPN transistor then allows

for charge to go to the gate of the MOSFET. When an

external storage capacitor is added to the CPC1580,

the photocurrent that is produced turns on the NPN

bipolar transistor and provides the charge (I x t = Q)

plus the charge of the capacitor to turn on the

MOSFET rapidly. If sufficient input control current is

not flowing, the LED is turned off, and gate current is

minimum forward voltage required and not enough

current being applied. This turns on the PNP bipolar

begins to charge. The value of the storage capacitor

should be equal to or greater than the MOSFET gate

capacitance: this will ensure proper operation. The

charge is sent through a bootstrap diode to prevent

the charge from escaping and discharging through a

turned-on MOSFET. The input control current is

applied, then the charge is transferred from the

storage capacitor through the NPN bipolar transistor,

along with the charge from the photovoltaics, to the

MOSFET gate to accomplish a rapid turn-on. After the

capacitor has discharged and the MOSFET has

turned on, the photocurrent from the input optocoupler

continues to flow into the gate to keep the MOSFET

turned on.

When the input control current is removed, the gate

current stops flowing and the PNP bipolar transistor is

on and is discharging the MOSFET gate. The

MOSFET is now off. At this point, the capacitor begins

to recharge for the next turn-on cycle.

4. Device Configuration

4.1 LED Resistor

LED resistor selection should comply with the

recommended operating conditions. This will provide

reliability to the design, and should help with

temperature. The CPC1580 is capable of being

operated at up to the maximum ratings, but this is not

recommended. It will shorten the life-span of the

device and could cause temperature problems that will

current is to provide for faster turn-on. Proper design

will have to be used to decide on the needs of the

application. The equation used to calculate the

resistor value:

4.2 Storage Capacitor Selection

on quickly by holding a reservoir of charge to be

transferred to the gate of the MOSFET. The turn-off

cycle does not depend on the storage capacitor.

The equation used to calculate the value of the charge

storage capacitor is:

(FARADS)