AN1162
DGD2005 Application Information
AN1162 – Rev 1
Application Note
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The DGD2005, High-side/Low-side gate driver is used to optimally drive the gate of MOSFETs or IGBTs. Below (Figure 1) is an example
application using DGD2005 with MOSFETs to make three half-bridge circuits used to drive a three phase motor. Typical motor applications
are AC Induction motors, PMSMs, and BLDC motors. DGD2005 can also be used in power supplies. In this document, the important
parameters needed to design in the DGD2005 are discussed. Main sections are bootstrap resistor, diode, and capacitor selection, gate
driver component selection, decoupling capacitor discussion, and PCB layout suggestions.
Figure 1. Three Phase Motor Driver application example of DGD2005
AN1162
AN1162 – Rev 1
Application Note
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March 2021
© Diodes Incorporated
Bootstrap Component Selection
Bootstrap Resistor
Considering Figure 1, when the low-side MOSFET (Q2, Q4, or Q6) turns on, Vs pulls to GND and the bootstrap capacitor (C
B1
, C
B2
, or C
B3
)
is charged. When the high-side MOSFET (Q1, Q3, or Q5) is turned on, V
S
swings above Vcc and the charge on the bootstrap capacitor (C
B
)
provides current to drive the IC high-side gate driver. The first charge of C
B
from Vcc through the bootstrap resistor (R
BS1
, R
BS2
, or R
BS3
) and
bootstrap diode (D
BS1
, D
BS2
, or D
BS3
) occurs when power is first applied and the low-side turns on the first time. At this time the charge
current is the largest as typically C
B
is not discharged fully at each cycle during normal operation.
A bootstrap resistor (R
BS
) is included in the bootstrap circuit to limit the inrush current that charges C
B
when Vs pulls below Vcc; this inrush
current is largest with the first charge. Limiting inrush current is desirable to limit noise spike on Vs and COM, potentially causing shoot-
through. The amplitude and length of time of the inrush current is determined mostly by the component value of R
BS
and C
BS
as well as Vcc
level. The aim in resistor selection for the application is to slow down the inrush current but have minimal effect on the RC time constant of
charging C
BS
.
Typically, values for R
BS
are 3Ω to 10Ω, enough to dampen the inrush current but have little effect on the V
BS
turn on. Figures 2-5 illustrate
the effect of different R
BS
values.
Figure 3. Bootstrap Peak inrush current ≈1.2A
with RBS=10Ω, CBS=2.2µF
Figure 4. VBS Rise Time (11.8µs) with
RBS=3Ω, CBS=2.2µF
Figure 5. VBS Rise Time (20.5µs) with
RBS=10Ω, CBS=2.2µF