A p p l i c at i o n N o t e
AN3018
IGBT/Power MOSFET Gate Drive Photocoupler
Technical Marketing Department
Compound Semiconductor Devices Business Division
Analog & Power Devices Business Unit
Renesas Electronics Corporation
1. Introduction
process proven in other Renesas Electronics IGBT-driving
The recent rise in awareness of environmental issues and
photocouplers , enabling both a high output current (IO =
the corresponding demand for energy savings has seen an
2.5 A MAX.) and low circuit current (ICC = 2 mA TYP.), which
increase in the use of inverter technology in a wide range of
enables high-temperature operation (TA = 110°C MAX.).
fields, including industrial machinery, power equipment, and
home appliances. The demand for industrial inverters such as
Figure 2-1. PS9505/PS9305 Equivalent Circuit
general-purpose inverters and AC servos is growing strongly
in the traditional European and North American markets and
8 Vcc
8 Vcc
NC 1
ANODE 1
UVLO
UVLO
is also taking off in emerging markets. Demand for inverter
7 Vo
7 Vo CATHODE 2
technology is also expected to grow in the expanding “clean ANODE 2
PD
PD
energy” fields of solar and wind power generation. One of CATHODE 3
6 VEE
6 Vo CATHODE 3
LED
LED
the most common semiconductor devices used in these
NC 4
NC 4
5 VEE
5 VEE
SHIELD
SHIELD
inverters is an IGBT (Insulated Gate Bipolar Transistor).
Signal
processing
circuit
Output
drive
circuit
PS9505
This application note describes the features and applications
of PS9505/PS9305 as an example to describe its
characteristics, its internal gate driving circuit and describe
the external gate resistance requirement and the details
of gate driver photocoupler power dissipation in relation
to MOSFET / IGBT gate charge based on desired switching
frequency to turn-on and turn-off the MOSFET / IGBT.
Table 1-1. Specification Outline of PS9505/PS9305
Part No.
PS9505Note 1
PS9305Note 1
Package
8-pin
DIP
6-pin
SDIP
BV (kVr.m.s.) VCC (V) IO (PEAK) ICCH/ICCL
IFLH
(mA)
MAX.
MAX
(A) MAX.
(mA) MAX.
5
35
2.5
3/3
5
5
35
2.5
3/3
5
MAX.
Note: 1. Built-in UVLO function
2. Product overview
Figure 2-1 shows the equivalent circuit of the PS9505/
PS9305. The PS9505 is an 8-pin DIP and the PS9305 is
an 8-pin SDIP high-speed photocoupler. These contain
a GaAIAs light emitting diode (LED) on the input side
and photo detector IC that integrates a photodiode (PD),
signal processing circuit, large-current circuit and UVLO
is configured on the side that outputs signals to the IGBT.
The photo detector IC is fabricated with the Bi-CMOS
Signal
processing
circuit
Output
drive
circuit
PS9305
Note: NC (No Connection) should be open or connect to ground of
LED side and should not connect to any bias voltage.
The features of the PS9505/PS9305 are listed below. Table 2-1
shows the truth table. For more feature details, refer to the data
sheet.
Features
• Large output peak current (IO = 2.5 A max.)
• High-speed switching (tPLH/tPHL =
tPLH/tPHL
CMH/CML
PWD (µS)
0.25μs max.)
(µs)
(kV/µs)
MAX.
MAX.
MIN.
• Large operating voltage range (VCC-VEE
= 15 to 30 V)
0.25/0.25
0.1
25/25
• Built-in UVLO(Under Voltage Lock Out)
0.25/0.25
0.1
25/25
function
• Low power consumption: ICCH, ICCL = 3
mA MAX.
• Long creepage distance (8 mm MIN.: PS9505L1, PS9505L2,
PS9305L2)
• Complies with international safety standards:
UL, VDE, CSA, SEMKO
• High instantaneous common mode rejection voltage (CMH, CML =±25 kV/μs min.)
• Operating Ambient Temperature ( TA = -40 to +110 °C)
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Table 2-1. Truth Table
VCC-VEE
Voltage Rise
Voltage Drop
(TURN-ON)
(TURN-OFF)
0 to 30 V
0 to 30 V
Output Voltage vs. Power Supply Voltage
14
L
ON
0 to 10.8 V
0 to 9.5 V
L
ON
10.8 to 13.4 V
9.5 to 12.5 V
TRANSITON
ON
13.4 to 30 V
12.5 to 30 V
Vo vs. VCC-VEE
Output (VO)
H
12
10
VO (V)
OFF
VCC-VEE
Output voltage Vo (V)
LED
Figure 3-1. Output Voltage vs. Power Supply Voltage
8
6
UVLO -
4
(11V)
2
0
3. UVLO (Under Voltage Lock Out) FUNCTION
0
5
UVLO +
(12.3V)
10
VCC-VEE (V)
15
20
Power supply voltage VCC-VEE (V)
The UVLO circuit holds VO at low level when the PS9505/
PS9305 power supply voltage is insufficient. If the IGBT’s
gate voltage (VO in the PS9505/PS9305) drops during
on state, the VCE (sat) of the IGBT becomes larger and
it might cause a large amount of power to dissipate,
leading to overheating and failure of the IGBT. To
prevent this, if the PS9505/PS9305 detects that its
power supply voltage (VCC2 – VE) is insufficient, it holds
VO at low level to protect the IGBT.
As shown in Figure 3-1, when the PS9505/PS9305 power
supply voltage (VCC2 – VE) is low (when the power supply
voltage is rising from 0 V), the PS9505/PS9305 holds the
VO output at low level until the voltage rises to VUVLO+, even
if the LED is on. Conversely, when the PS9505/PS9305
power supply voltage (VCC2 – VE) is falling (changing to
a negative voltage) the VO output is high level until the
voltage reaches VUVLO–, but if the voltage falls below VUVLO–,
the PS9505/PS9305 pulls the VO output down to low level
even if the LED is on.
Therefore, if the PS9505/PS9305 power supply voltage
(VCC2 – VE) falls below VUVLO– (9.5 to 12.5 V) due to some
error, the VO output of the PS9505/PS9305 will go low
even if the LED is on. When the power supply voltage
(VCC2 – VE) subsequently rises to above VUVLO+ (10.8 to 13.4
V), the VO output goes high again (with the LED on).
4. DESIGN OF IGBT GATE DRIVE CIRCUIT
+5V
LEDH
PS9505
Vcc=15V
0.1uF
+HV DC (P line)
RG
LEDL
3-phase output
VEE=-5V
-HV DC (N line)
Figure 4-1 shows an example of an IGBT drive circuit using the PS9505. The gate resistance settings described
in sections 4.1 and 4.2 are implemented. PS9305 can be
used with same circuit to change pin 6 to VEE, pin 1 to
LEDH and pin 2 to LEDL.
4.1. Calculation of Minimum Value of IGBT
external Gate Resistance RG
(1) Calculation from the photocoupler side
The external gate resistor (RG) must be selected so that
the peak output current of the PS9505/PS9305
(IOL(PEAK)) does not exceed its maximum rating. The
minimum value of the gate resistor (RG) can be
approximated by using the following expression:
RG ≥ {(VCC2 – VEE) – VOL}/IOL(PEAK)·····(4.1)
VCC2 – VEE: PS9505/PS9305 power supply difference (VEE =
0 when not using a negative power supply)
VOL: PS9505/PS9305 low-level output voltage. Calculate
the minimum value of the external gate resistor (RG) under
the following conditions:
IOL(PEAK) = 2.5 A
VCC2 – VEE = 20 V
Voltage drops to VOL = 3.5 V at TA = -40 °C (as a worst
case) while IOL = 2.5 A. Characteristics curves showing the
relationship between the low-level output voltage (VOL)
and low-level
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output current (IOL) are provided in Figure 4.2 for reference.
These settings make allowances for operation
under low temperatures (–40°C).
Note that because the low-side MOSFET voltage drops
more than the high-side MOSFET voltage in the
PS9505/PS9305, the minimum value of the external gate
resistor (RG) is calculated based on the low-side MOSFET.
From equation (4.1):
RG ≥ {(VCC2 – VEE) – VOL}/IOL(PEAK)
= (20 – 3.5)/2.5
= 6.6 Ω
LOW LEVEL OUTPUT VOLTAGE vs. LOW LEVEL OUTPUT CURRENT
Low Level Output Voltage VOL (V)
8
6
VCC= 30V,
VEE= GND,
IF= 0 mA
Ta= +110˚C
Ta= +25˚C
4
4.2 Checking the allowable dissipation of the
PS9505/PS9305 and adjusting RG
2
Ta= -40˚C
0
0.0
0.5
1.0
1.5
2.0
2.5
Low Level Output Current IOL (A)
Figure 4-2. VOL vs. IOL Characteristics
VGS
Gate-Source Voltage (V)
(2) Calculation from the IGBT side
The charge characteristics of the IGBT’s gate are described
in the IGBT’s data sheet, but in general, the characteristics
curve is as shown in Figure 4-3.
Qg
(IG) is indicated by:
IG = QG/ts
Because a constant driving voltage V(DR) is used, the relationship between the gate peak current and the total gate
resistance (Rg) is as follows:
Rg = V(DR)/IG, with Rg indicating the sum of the
driver’s output impedance, the external gate resistance, and
the gate’s own series resistance.
Therefore, in order to satisfy the switching time required
by the system, the external gate resistance calculated from
the photocoupler side (RG) must be smaller than the total
gate resistance calculated from the IGBT side (Rg). If ts is
unable to be satisfied, you will have to consider selecting a
photocoupler that can drive a larger current, or attaching an
external current amplifier (buffer).
V(DR)
=Peak drive voltage
Qgd
Qgs
Qg, Charge (nC)
Figure 4-3. VGS vs. Qg Characteristics
In this graph:
Qge is the charge between the gate and the emitter
Qcg is the charge between the collector and the gate
Qg is the total gate charge
The gate charge is expressed as follows:
Q = C x V, with Q indicating the total charge.
The relationship between the gate capacitance, the switching time, and the gate driving current is as follows:
dQ/dt = C x dV/dt = I
In this case, if ts represents the switching time required by
the system, the current that must be supplied to the gate
The power consumption of the PS9505/PS9305 (PT) is a
total of the power consumption of the LED on the input side
(primary side) (PD) and the power consumption of the photo
detector IC on the output side (secondary side) connected
to the IGBT (PO).
PT = PD + PO·····(4.2.1)
(1) LED power consumption
The power consumption of the LED on the input side
(primary side) (PD) is calculated as follows:
PD = IF x VF x Duty ratio·····(4.2.2)
(2) Photo detector IC power consumption
The power consumption of the photo detector IC on the
output side (secondary side) (PO) is calculated as follows:
PO = PO(Circuit) + PO(Switching)·····(4.2.3)
PO(Circuit) is the circuit power consumption of the photo
detector IC (the power consumed by ICC2).
PO(Switching) is the power consumption of the photo detector
IC required to charge and discharge the gate capacitor (the
power consumed by IO).
1. Circuit power consumption of photo detector IC: Po(Circuit)
PO(Circuit) = ICC2 x (VCC2 – VEE)·····(4.2.4)
ICC2 is the circuit current supplied to the photo detector IC.
VCC2 – VEE is the power supply difference of the photo
detector IC.
2. Power consumption of photo detector IC required to
charge and discharge the IGBT gate capacitor
PO(Switching) = Esw(RG, QG) x fSW·····(4.2.5)
ESW(RG, QG) is the per-cycle power consumed when
charging the IGBT gate capacitor (see Figure 4.4 and Figure
4.5). fSW is the switching frequency.
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= 16mA x 1.8 V x 0.8 = 23 mW
2. Power consumption of output side (secondary side,
photo detector IC) (PO)
From the calculation in (4.2.6):
PO = ICC2 x (VCC2 – VEE) + Esw(RG, QG) x fSW
= 3 mA x 20 V +3.5µJ x 20 kHz
= 60 mW + 70 mW
= 130 mW < 178 mW for PS9505
= 130 mW < 220 mW for PS9305
(absolute maximum allowable dissipation for photo
detector IC when TA = 85˚C)
Vo
Io
Po (= Io x Vo)
Esw (on)
Esw (off)
Esw (Qg, RG) = Esw (on) + Esw (off)
The external gate resistance RG has a significant effect on
the performance of the IGBT, so be sure to select the right
gate resistor for your gate driver design. A smaller gate
resistance means faster switching to charge and discharge
the IGBT’s input capacitor, which leads to lower switching
dissipation. However, a smaller gate resistance also leads to
a larger voltage variation (dV/dt) and current variation (di/
dt) during switching. It is therefore important to evaluate
the actual operation of the IGBT by referring to the relevant
technical documents before selecting the gate resistor.
Figure 4-4. Power Consumption Waveform During
Switching of PS9505/PS9305
Energy Per Switching Cycle Esw [μJ]
8
Qg= 1000nC
7
Qg= 500nC
Qg= 100nC
6
5
4
3
5. PS9505/PS9305 PERIPHERAL CIRCUIT
2
1
0
0
10
20
30
40
50
Gate Resistance RG [Ω]
Figure 4-5. Switching Loss per Cycle of PS9505/PS9305
3. Power consumption of photo detector IC
From the calculations in (4.2.3), (4.2.4) and (4.2.5), the
power consumption of the photo detector IC is as follows:
PO = PO(Circuit) + PO(Switching)
= ICC2 x (VCC2 – VEE) + Esw(RG, QG) x fSW·····(4.2.6)
(3) Checking the allowable dissipation of the PS9505/
PS9305 and adjusting RG
When used in the circuit shown in Figure 4-1, the power
consumption of the PS9505/PS9305 is as follows,
calculated under the conditions of
RG = 6.6 Ω, Duty (MAX.) = 80%, QG = 500 nC,
f =20 kHz, IF (MAX.) = 16 mA, and TA = 85˚C:
1. Power consumption of input side (primary side, LED) (PD)
From the calculation in (4.2.2):
PD = IF x VF x Duty ratio
5.1 Layout
1. To minimize floating capacitance between the primary
side and the secondary side (the input and the output), be
sure to place the circuits so that they are not too close to
the primary-side and secondary-side wiring patterns on the
board, and that there is no cross-wiring if multi-layer wiring
is being used.
2. To prevent transient noise from the IGBT from affecting
the PS9505/PS9305, keep the IGBT collector/emitter circuit
pattern and DC lines (P and N lines) of the inverter circuit
through which a large current flows as far away as possible
from the PS9505/PS9305 LED driver and VCC2 and VO lines.
3. Design the layout of the bypass capacitor (0.1 μF or
higher) between VCC – VEE on the secondary side (output
side) of the PS9505/PS9305 so as to be as close as possible
to the VCC (pin 8) and VEE (pin 5) of the PS9505/PS9305 (so
that the PS9505/PS9305 pins and capacitor pins are as
close as possible).
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5.2 LED driver
Design the LED driver so that the recommended current (IF)
and voltage (VF) are applied to the LED. Table 5-1 shows the
recommended operating conditions for the LED.
Item
Symbol
MIN.
Input voltage (OFF) VF (OFF)
-2
Input current (ON)
7
IF (ON)
TYP.
10
MAX.
Unit
0.8
V
16
mA
Table 5-1. Recommended Operating Conditions
for PS9505/PS9305 LED
To ensure that the LED is turned off properly, even if
common mode noise (CML) occurs, we recommend applying
a reverse bias to the LED within the range indicated by
the recommended operating conditions in Table 5-1.
Similarly, to ensure that the LED is turned on properly,
even if common mode noise (CMH) occurs, we recommend
specifying as large a LED current (IF) as possible, within the
range indicated by the recommended operating conditions
in Table 5-1.
6. Specifying dead time
As shown in Figure 6.1, in the inverter circuit, IGBT 1 and
IGBT 2 on the upper and lower arms alternately switch on
and off, outputting a signal to the motor or other load. If
there is insufficient dead time, IGBT 1 and IGBT 2 on the
upper and lower arms switch on at the same time, causing a
short-circuit current to flow, damaging the IGBTs (see Figure
6.2, example of PS9505).
+HV DC (P line)
PS9505 No1
IGBT1
ON Upper arm
PS9505 No2
IGBT2
OFF Lower arm
Output
-HV DC (N line)
Figure 6.1 Inverter Circuit Operating Normally
+HV DC (P line)
PS9505 No1
IGBT1
ON Upper arm
PS9505 No2
IGBT2
ON Lower arm
Output
of the PS9505/PS9305 and the IGBT (toff total MAX.) and the
minimum value of the total turn-on time of the PS9505/PS9305
and the IGBT (ton total MIN.),or higher.
tdead ≥ toff total MAX. – ton total MIN.
= (tPHL MAX.(PC) + toff MAX.(IGBT)) – (tPLH MIN.(PC) + ton MIN.(IGBT))
= (tPHL MAX.(PC) – tPLH MIN.(PC)) + (toff MAX.(IGBT) – ton MIN.(IGBT))
= PDD (PC) + (toff MAX. – ton MIN.) (IGBT)
In the above equation, (PC) is the response time of the PS9505/
PS9305 photocoupler and (IGBT) is the response time of the
IGBT.
PS9505 No1
(Upper arm)
PS9505 No2
(Lower arm)
IF
tdead
t
IF
t
IGBT 1
(Upper arm)
Io
IGBT 2
(Lower arm)
Io
t
t
}
}
Photocoupler input signal
(LED input signal)
IGBT output current
Figure 6-3. Deadtime (tdead)
In the PS9505/PS9305, the transmission delay time
difference between any two parts has been prescribed
to make specifying dead time easy (this time is PDD =
tPHL – tPLH = ±100 ns). See the PS9505/PS9305 data sheet
for details. Note that PDD in the PS9505/PS9305 must be
measured under the same temperature and measurement
conditions as tPHL and tPLH. The board must therefore be laid
out so that the ambient conditions of the upper and lower
arms of the photocoupler are the same. Also be sure to
thoroughly
evaluate the dead time using the actual device, and allow a
sufficient margin in your design.
7. CALCULATION OF JUNCTION TEMPERATURE
1. PS9505/PS9305 thermal resistance model
LED
TJE
Photo detector IC
TJD
02
01
03
-HV DC (N line)
Figure 6.2 Inverter Circuit When Short-Circuit Occurs
Dead time (tdead) (see Figure 6.3, example of PS9505) is
specified in order to prevent IGBT1 (upper arm) and IGBT2
(lower arm) turning on at the same time, and is usually the
difference between the maximum value of the total turn-off time
Ta
Figure 7-1. Thermal Resistance Model of PS9505/PS9305
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Figure 7.1 shows the thermal resistance model of the
PS9505/PS9305. The model used has two heat sources: the
LED and the photo detector IC.
TJE … LED junction temperature
TJD … Light receiving IC junction temperature
Ta … Ambient temperature
θ1 … Thermal resistance between LED-ambient temperature
θ2 … Thermal resistance between LED-light receiving IC
θ3 … Thermal resistance between light receiving IC-ambient temperature
2. Junction temperature calculation
In the above model, the junction temperature of LED and
photo detector IC is calculated as follows:
TJE = R11 x PE + R12 x PD + TA … (7.1)
TJD = R21 x PE + R22 x PD + TA … (7.2)
PE … Power consumption of LED
PD … Power consumption of light receiving IC
R11 … LED-ambient temperature thermal resistance
parameter (R11 = θ1 || (θ2 + θ3))
R12, R21 … LED-light receiving IC thermal resistance
parameter (R12, R21 = (θ1 x θ3)/(θ1 + θ2 + θ3))
R22 … Light receiving IC-ambient temperature
thermal resistance parameter (R22 = θ3 || (θ1 + θ2))
Table 7-1. Thermal Resistance Parameter
Thermal Resistance Parameter (˚C/W)
R11
R12, R21
R22
PS9505 TYP.
244
136
182
PS9305 TYP.
293
124
166
Also an example of PS9305, calculating the junction
temperature using (7.1) and (7.2), with PE = 27mW, PO
(=PD) = 124 mW, and TA = 85°C:
TJE TJD = R11 x PE + R12 x PD + TA
= 293°C/W x 27 mW + 124°C/W x 124 mW + 85°C
= 108.3°C
= R21 x PE + R22 x PD +TA
= 124°C/W x 27 mW + 166°C/W x 124 mW + 85°C
= 108.9°C
Set junction temperatures TJE and TJD to values lower than
125°C.
8. Summary
This application note describes the features and
applications of the PS9505/PS9305 photocoupler, which is
an IGBT-driving photocoupler with built-in IGBT protection
circuits. Please use this document when designing your
system. The PS9505/PS9305 aims to facilitate the design
of inverter equipment—a market that is expected to grow
significantly in the future and contribute to reducing system
scale. In addition to aggressively marketing the PS9505/
PS9305, Renesas Electronics also plans to continue
developing photocouplers that support high-temperature
operation and high-output devices.
The following is an example of PS9505, calculating the
junction temperature using (7.1) and (7.2), with PE = 27mW,
PO ( =PD) = 124 mW, and TA = 85°C:
TJE TJD = R11 x PE + R12 x PD + TA
= 244°C/W x 27 mW + 136°C/W x 124 mW + 85°C
= 108.5°C
= R21 x PE + R22 x PD +TA
= 136°C/W x 27 mW + 182°C/W x 124 mW + 85°C
= 111.2°C
Information and data presented here is subject to change without notice. California
Eastern Laboratories assumes no responsibility for the use of any circuits described
herein and makes no representations or warranties, expressed or implied, that such
circuits are free from patent infringement.
© California Eastern Laboratories 12/1/11
4590 Patrick Henry Drive, Santa Clara, CA 95054
Tel. 408-919-2500
FAX 408-988-0279 www.cel.com
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