HCPL3150 datasheet(11/15 Pages) HP

11 / 15 page

1-207

Figure 26. HCPL-3150 Typical Application Circuit with Negative IGBT Gate Drive.

Selecting the Gate Resistor

(Rg) to Minimize IGBT

Switching Losses.

Step 1: Calculate Rg Minimum

From the IOL Peak Specifica-

tion. The IGBT and Rg in Figure

26 can be analyzed as a simple

RC circuit with a voltage supplied

by the HCPL-3150.

(VCC – VEE - VOL)

≥ –––––––––––––––

IOLPEAK

(VCC – VEE - 1.7 V)

= ––––––––––––––––

IOLPEAK

(

15 V + 5 V - 1.7 V)

= ––––––––––––––––––

0.6 A

= 30.5

Ω

The VOL value of 2 V in the pre-

vious equation is a conservative

value of VOL at the peak current

of 0.6 A (see Figure 6). At lower

Rg values the voltage supplied by

the HCPL-3150 is not an ideal

voltage step. This results in lower

peak currents (more margin)

than predicted by this analysis.

When negative gate drive is not

used VEE in the previous equation

is equal to zero volts.

Step 2: Check the HCPL-3150

Power Dissipation and

Increase Rg if Necessary. The

HCPL-3150 total power dissipa-

tion (PT) is equal to the sum of

the emitter power (PE) and the

output power (PO):

PT = PE + PO

PE = IF •VF •Duty Cycle

PO = PO(BIAS) + PO (SWITCHING)

= ICC•(VCC - VEE)

+ ESW(RG, QG)•f

For the circuit in Figure 26 with IF

(worst case) = 16 mA, Rg =

30.5

Ω, Max Duty Cycle = 80%,

Qg = 500 nC, f = 20 kHz and TA

max = 90

°C:

PE = 16 mA•1.8 V•0.8 = 23 mW

PO = 4.25 mA•20 V

4.0

µJ•20 kHz

85 mW + 80 mW

165 mW

154 mW (PO(MAX) @ 90°C

250 mW

−20C•4.8 mW/C)

PO Parameter

Description

ICC

Supply Current

VCC

Positive Supply Voltage

VEE

Negative Supply Voltage

ESW(Rg,Qg)

Energy Dissipated in the HCPL-3150 for each

IGBT Switching Cycle (See Figure 27)

Switching Frequency

Parameter

Description

LED Current

LED On Voltage

Duty Cycle

Maximum LED

Duty Cycle

+ HVDC

3-PHASE

- HVDC

0.1 µF

VCC = 15 V

–

HCPL-3150

VEE = -5 V

–

270

Ω

+5 V

CONTROL

INPUT

74XXX

OPEN

COLLECTOR

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