HCPL-3150 datasheet(12/15 Pages) HP

12 / 15 page

1-208

The value of 4.25 mA for ICC in

the previous equation was

obtained by derating the ICC max

of 5 mA (which occurs at -40

°C)

to ICC max at 90°C (see Figure 7).

Since PO for this case is greater

than PO(MAX), Rg must be

increased to reduce the HCPL-

3150 power dissipation.

PO(SWITCHING MAX)

= PO(MAX) - PO(BIAS)

= 154 mW - 85 mW

= 69 mW

PO(SWITCHINGMAX)

ESW(MAX) = –––––––––––––––

69 mW

= ––––––– = 3.45

µJ

20 kHz

For Qg = 500 nC, from Figure

27, a value of ESW = 3.45 µJ

gives a Rg = 41

Ω.

Thermal Model

The steady state thermal model

for the HCPL-3150 is shown in

Figure 28. The thermal resistance

values given in this model can be

used to calculate the tempera-

tures at each node for a given

operating condition. As shown by

the model, all heat generated

flows through

CA which raises

the case temperature TC

accordingly. The value of

depends on the conditions of the

board design and is, therefore,

determined by the designer. The

value of

CA = 83°C/W was

obtained from thermal measure-

ments using a 2.5 x 2.5 inch PC

board, with small traces (no

ground plane), a single HCPL-

3150 soldered into the center of

the board and still air. The

absolute maximum power

dissipation derating specifications

assume a

CAvalue of 83°C/W.

Inserting the values for

LC and

DC shown in Figure 28 gives:

TJE = PE•(230°C/W + θCA)

+ PD•(49°C/W + θCA) + TA

TJD = PE•(49°C/W + θCA)

+ PD•(104°C/W + θCA) + TA

For example, given PE = 45 mW,

PO = 250 mW, TA = 70°C and θCA

= 83

°C/W:

shown in Figure 29. The HCPL-

3150 improves CMR performance

by using a detector IC with an

optically transparent Faraday

shield, which diverts the capaci-

tively coupled current away from

the sensitive IC circuitry. How

ever, this shield does not

eliminate the capacitive coupling

between the LED and optocoup-

ler pins 5-8 as shown in

Figure 30. This capacitive

coupling causes perturbations in

the LED current during common

mode transients and becomes the

major source of CMR failures for

a shielded optocoupler. The main

design objective of a high CMR

LED drive circuit becomes

keeping the LED in the proper

state (on or off) during common

mode transients. For example,

the recommended application

circuit (Figure 25), can achieve

15 kV/

µs CMR while minimizing

component complexity.

Techniques to keep the LED in

the proper state are discussed in

the next two sections.

From the thermal mode in Figure

28 the LED and detector IC

junction temperatures can be

expressed as:

TJE = PE •(θLC||(θLD + θDC) + θCA)

•

+ PD•

(–––––––––––––––– + θ

) + T

LC + θDC + θLD

•

TJD = PE

(––––––––––––––– + θ

)

LC + θDC + θLD

PD•(θDC||(θLD + θLC) + θCA) + TA

TJE and TJD should be limited to

125

°C based on the board layout

and part placement (

CA) specific

to the application.

LED Drive Circuit

Considerations for Ultra

High CMR Performance

Without a detector shield, the

dominant cause of optocoupler

CMR failure is capacitive

coupling from the input side of

the optocoupler, through the

package, to the detector IC as

TJE = PE•313°C/W + PD•132°C/W + TA

= 45 mW•313

°C/W + 250 mW

•132

°C/W + 70°C = 117°C

TJD = PE•132°C/W + PD•187°C/W + TA

= 45 mW•132C/W + 250 m

•187

°C/W + 70°C = 123°C

Figure 27. Energy Dissipated in the

HCPL-3150 for Each IGBT Switching

Cycle.

Rg – GATE RESISTANCE –

Ω

100

Qg = 100 nC

Qg = 250 nC

Qg = 500 nC

VCC = 19 V

VEE = -9 V

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