Renesas ISL71040MEV1Z User Manual
User Manual
ISL71040MEV1Z
Evaluation Board
The ISL71040MEV1Z evaluation platform is designed to evaluate the ISL71040M. The ISL71040M is designed to
drive enhancement mode Gallium Nitride (GaN) FETs in isolated topologies and boost type configurations. It
operates across a supply range of 4.5V to 13.2V and offers both non-inverting and inverting inputs to satisfy
non-inverting and inverting gates drive within a single device. The ISL71040M has a 4.5V gate drive voltage
(V
) that is generated using an internal regulator that prevents the gate voltage from exceeding the maximum
DRV
gate-to-source rating of enhancement mode GaN FETs. The gate drive voltage also features an Undervoltage
Lockout (UVLO) protection that ignores the inputs (IN/INB) and keeps OUTL turned on to ensure the GaN FET is
in an OFF state whenever VDRV is below the UVLO threshold. The ISL71040M inputs can withstand voltages up
to 14.7V regardless of the V
controllers. The split outputs of the ISL71040M offer the flexibility to adjust the turn-on and turn-off speed
independently by adding additional impedance to the turn-on/off paths.
Key Features
•Wide VDD range single
○ 4.5V to 13.2V
voltage. This allows the ISL71040M inputs to be connected directly to most PWM
DD
• Location provided for load resistors to switch the GaN FET with a load
• SMA connector on the gate drive voltage to analyze the gate waveforms
• Drain/source sense test points to analyze the drain to source waveforms
• Banana jack connectors for power supplies and drain/source connections
Specifications
•VDD range: 4.5V to 13.2V
Ordering Information
Part Number Description
ISL71040MEV1Z ISL71040MEV1Z evaluation board
Related Literature
For a full list of related documents, visit our website:
• ISL71040M
device page
R12UZ0042EU0200 Rev.2.0 Page 1
Feb.9.21 Copyright © 2019
ISL71040MEV1Z 1. Functional Description
1. Functional Description
The ISL71040M is a single channel, high speed enhanced mode GaN FET low-side driver for isolated power
supplies and Synchronous Rectifier (SR) applications.
The inputs stage can handle inputs to the 14.7V independent of V
and offers both inverting and non-inverting
DD
inputs. The split output stage is capable of sourcing and sinking high currents and allows for independent tuning of
the turn-on and turn-off times. A typical propagation delay of 36ns enables high switching frequency operation.
1.1 Operating Range
The ISL71040M offers a wide operating supply range of 4.5V to 13.2V. The gate drive voltage is generated from
an internal linear regulator to keep the gate-source voltage below the absolute maximum level of 6V for the
ISL7002xSEH GaN FET devices.
1.2 Quick Start Guide
1. Apply 5.0V to VDD.
2. Drive the IN or INB driver inputs.
a. To drive INB, populate R
3. Monitor the gate transition waveforms using SP
a. Use a low capacitance SMA cable to reduce the rise and fall times.
b. Use a scope probe with a short ground loop soldered to the outside of the SMA connector.
4. Monitor the V
voltage using TP10 and TP11 with a short ground loop connection on a scope probe.
DS
5. Switch the FET with a load using R
a. C
counter any cable inductance leading up the J3 and prevent drain-to-source voltage spikes that can
3:C8
damage the GaN FET.
with a 0Ω resistor and remove the 0Ω resister on R2.
1
.
3
, R6, and R7.
5
6. Use SP
and SP2 to sense the current traveling through the FET.
1
1.3 Gate Drive for N-Channel GaN FETs
New technologies based on wide bandgap semiconductors produce High Electron Mobility Transistors (HEMT).
An example of a HEMT is the GaN based power transistors such as the ISL73023SEH, which offer very low
r
DS(ON)
frequency operation while avoiding significant efficiency loss. However, GaN power FETs have special
requirements in terms of gate drive that the ISL71040M is designed to specifically address.
Key properties of a gate driver for GaN FETs are:
• Gate drive signals need to be sufficiently higher than the V
• A well regulated gate drive voltage to keep the V
• Split pull-up and pull-down gate connections to add series gate resistors that independently adjust turn-on and
• Driver pull-down resistance < 0.5Ω that eliminates undesired Miller turn-on
• High current source/sink capability and low propagation delay achieve high switching frequency operation
and gate charge (Qg). These attributes make the devices capable of supporting very high switching
threshold specified in GaN FET datasheets for
GS
proper operation
lower than specified absolute maximum level of 6V
GS
turn-off speed. This eliminates the need of a series diode whose voltage drop can cause an insufficient gate
drive voltage
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Feb.9.21
ISL71040MEV1Z 1. Functional Description
1.4 Undervoltage Lockout
The VDD pin accepts a recommended supply voltage range of 4.5V to 13.2V and is the input to the internal linear
regulator. VDRV is the output of the regulator and is equal to 4.5V. VDRV provides the bias for all internal circuitry
and the gate drive voltage for the output stage.
UVLO circuitry monitors the voltage on VDRV and is designed to prevent unexpected glitches when VDD is being
turned on or turned off. When VDRV < ~1V, an internal 500Ω resistor connected between OUTL and ground helps
keep the gate voltage close to ground. When ~1.2V < VDRV < UV, OUTL is driven low while ignoring the logic
inputs and OUTH is in a high impedance state. This low state has the same current sinking capacity as during
normal operation. This ensures that the driven FETs are held off even if there is a switching voltage on the drains
that can inject charge into the gates from the Miller capacitance.
When VDRV > UVLO, the outputs now respond to the logic inputs. In the non-inverting operation (PWM signal
applied to IN pin) the output is in-phase with the input. In the inverting operation (PWM signal applied to INB pin)
the output is out-phase with the input.
For the negative transition of VDD through the UV lockout voltage, the OUTL is active low and OUTH is high
impedance when VDRV < ~3.7VDC regardless of the input logic states.
1.5 Input Stage
The input threshold of the ISL71040M is based on a TTL and CMOS compatible input threshold logic that is
independent of the supply voltage. With typical high threshold = 1.7V and typical low threshold = 1.4V, the logic
level thresholds can be conveniently driven with PWM control signals derived from 3.3V and 5V power controllers.
The ISL71040M offers both inverting and non-inverting inputs. The state of the output pin is dependent on the
bias on both input pins. Tab le 1
summarizes the inputs to output relation.
Table 1. Truth Table
IN INB OUT OUTH OUTL
000Hi-Z0
010Hi-Z0
1011Hi-Z
110Hi-Z0
Note: OUT is the combination of OUTH and OUTL connected together. Hi-Z represents a high impedance state.
As a protection mechanism, if any of the input pins are left in a floating condition, OUTL is held in the low state
and OUTH is high impedance. This is achieved using a 300kΩ pull-up resistor from INB to VDD and a 300kΩ
pull-down resistor from the IN pin to VSS. For proper operation in non-inverting applications, INB should be
connected to VSS. For inverting applications, IN should be connected to VDD for proper operation.
1.6 Enable Function
An enable or disable function can be easily implemented in ISL71040M using the unused input pin. The following
tips describe how to implement an enable/disable function:
• In a non-inverting configuration, the INB pin can be used to implement the enable/disable function. OUT is
enabled when INB is biased low, acting as an active low enable pin
• In an inverting configuration, the IN pin can be used to implement the enable and disable function. OUT is
enabled when IN is biased high, acting as an active high enable pin
R12UZ0042EU0200 Rev.2.0 Page 3
Feb.9.21
ISL71040MEV1Z 1. Functional Description
(EQ. 1)
P
D
2Qcfreq V
GS
R
gate
R
gaterDS ON
+
---------------------------------------------
I
DD
freqVDD+=
1.7 Driver Power Dissipation
The ISL71040M power dissipation is dominated by the losses associated with the gate charge of the driven bridge
FETs and the switching frequency. The internal bias current also contributes to the total dissipation but is usually
not significant compared to the gate charge losses.
For example, the ISL73023SEH has a total gate charge of 13nC when V
= 50V and V
DS
= 4.5V. This is the
GS
charge that a driver must source to turn on the GaN FET and must sink to turn off the GaN FET.
Equation 1
calculates the power dissipation of the driver:
where:
freq = Switching frequency
V
= V
GS
Q
= Gate charge for V
c
bias of the ISL71040M
DRV
GS
IDD(freq) = Bias current at the switching frequency
r
R
= ON-resistance of the driver
DS(ON)
= External gate resistance (if any)
gate
Note that the gate power dissipation is proportionally shared with the external gate resistor. Do not overlook the
power dissipated by the external gate resistor.
R12UZ0042EU0200 Rev.2.0 Page 4
Feb.9.21
ISL71040MEV1Z 2. General PCB Layout Guidelines
2. General PCB Layout Guidelines
The AC performance of the ISL71040M depends significantly on the design of the Printed Circuit Board (PCB).
The following layout design guidelines are recommended to achieve optimum performance:
• Place the driver as close as possible to the driven power FET.
• Understand where the switching power currents flow. The high amplitude di/dt currents of the driven power FET
induces significant voltage transients on the associated traces.
• Keep power loops as short as possible by paralleling the source and return traces.
• Use planes where practical; they are usually more effective than parallel traces.
• Avoid paralleling high amplitude di/dt traces with low level signal lines. High di/dt induces currents and
consequently, noise voltages in the low level signal lines.
• When practical, minimize impedances in low level signal circuits. The noise, magnetically induced on a 10kΩ
resistor, is 10 times larger than the noise on a 1kΩ resistor.
• Be aware of magnetic fields emanating from transformers and inductors. Gaps in the magnetic cores of these
structures are especially bad for emitting flux.
• If you must have traces close to magnetic devices, align the traces so that they are parallel to the flux lines to
minimize coupling.
• The use of low inductance components such as chip resistors and chip capacitors is highly recommended.
• Use decoupling capacitors to reduce the influence of parasitic inductance in the V
be effective, these capacitors must also have the shortest possible conduction paths. If vias are used, connect
several paralleled vias to reduce the inductance of the vias.
• It may be necessary to add resistance to dampen resonating parasitic circuits, especially on OUTH. If an
external gate resistor is unacceptable, then the layout must be improved to minimize lead inductance.
• Keep high dv/dt nodes away from low level circuits. Guard banding can be used to shunt away dv/dt injected
currents from sensitive circuits. This is especially true for control circuits that source the input signals to the
ISL71040M.
• Avoid having a signal ground plane under a high amplitude dv/dt circuit. This injects di/dt currents into the signal
ground paths.
• Calculate power dissipation and voltage drop for the power traces. Many PCB/CAD programs have built in tools
for trace resistance calculation.
• Large power components (such as power FETs, electrolytic caps, and power resistors) have internal parasitic
inductance which cannot be eliminated. This must be accounted for in the PCB layout and circuit design.
• If you simulate your circuits, consider including parasitic components, especially parasitic inductance.
• The GaN FETs have a separate substrate connection that is internally tied to the source pin. Source and
substrate should be at the same potential. Limit the inductance in the OUTH/L to Gate trace by keeping it as
short and thick as possible.
, VDD, and GND leads. To
DRV
R12UZ0042EU0200 Rev.2.0 Page 5
Feb.9.21
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