ADP3419 Analog Devices, ADP3419 Datasheet - Page 11

• Manufacturer Part Number: ADP3419
• Description: High Voltage MOSFET Driver
• Manufacturer: Analog Devices

www.datasheet4u.com
APPLICATION INFORMATION
SUPPLY CAPACITOR SELECTION
For the supply input (VCC) of the ADP3419, a local bypass
capacitor is recommended to reduce the noise and to supply
some of the peak currents drawn. Use a 10 µF or 4.7 µF
multilayer ceramic (MLC) capacitor. MLC capacitors provide
the best combination of low ESR and small size, and can be
obtained from the following vendors.
Table 5.
Vendor
Murata
Taiyo-Yuden
Tokin
Keep the ceramic capacitor as close as possible to the ADP3419.
BOOTSTRAP CIRCUIT
The bootstrap circuit uses a charge storage capacitor (C
a Schottky diode (D1), as shown in Figure 17. Selection of these
components can be done after the high-side MOSFET has been
chosen. The bootstrap capacitor must have a voltage rating that
is able to handle at least 5 V more than the maximum supply
voltage. The capacitance is determined by
where:
Q
∆V
drive.
For example, two IRF7811 MOSFETs in parallel have a total
gate charge of about 36 nC. For an allowed droop of 100 mV,
the required bootstrap capacitance is 360 nF. A good quality
ceramic capacitor should be used, and derating for the signifi-
cant capacitance drop of MLCs at high temperature must be
applied. In this example, selection of 470 nF or even 1 µF would
be recommended.
A Schottky diode is recommended for the bootstrap diode due
to its low forward drop, which maximizes the drive available for
the high-side MOSFET. The bootstrap diode must also be able
to handle at least 5 V more than the maximum battery voltage.
The average forward current can be estimated by
where f
controller.
HSGATE
BST
C
I
is the voltage droop allowed on the high-side MOSFET
F
BST
(
MAX
is the total gate charge of the high-side MOSFET.
AVG
=
is the maximum switching frequency of the
)
=
Q
∆
Q
HSGATE
V
HSGATE
BST
Part Number
GRM235Y5V106Z16
EMK325F106ZF
C23Y5V1C106ZP
×
f
MAX
Web Address
www.murata.com
www.t-yuden.com
www.tokin.com
BST
) and
(1)
(2)
Rev. A | Page 11 of 16
POWER AND THERMAL CONSIDERATIONS
The major power consumption of the ADP3419-based driver
circuit is from the dissipation of MOSFET gate charge. It can be
estimated as
where:
VCC is the supply voltage 5 V.
f
Q
low-side MOSFETs, respectively.
For example, the ADP3419 drives two IRF7821 high-side
MOSFETs and two IRF7832 low-side MOSFETs. According to
the MOSFET data sheets, Q
68 nC. Given that f
130 mW.
Part of this power consumption generates heat inside the
ADP3419. The temperature rise of the ADP3419 against its
environment is estimated as
where θ
given in the absolute maximum ratings as 220°C/W for a
4-layer board.
The total MOSFET drive power dissipates in the output
resistance of ADP3419 and in the MOSFET gate resistance as
well. η represents the ratio of power dissipation inside the
ADP3419 over the total MOSFET gate driving power. For
normal applications, a rough estimation for η is 0.7. A more
accurate estimation can be calculated using
where:
R1 and R2 are the output resistances of the high-side driver:
R3 and R4 are the output resistances of the low-side driver:
R is the external resistor between the BST pin and the BST
capacitor.
R
MOSFETs, respectively.
Assuming that R = 0 and that R
gives a value of η = 0.71. Based on Equation 4, the estimated
temperature rise in this example is about 22°C.
MAX
HSGATE
R1 = 1.7 (DRVH − BST), R2 = 0.8 (DRVH − SW).
R3 = 1.7 (DRVL − VCC), R4 = 0.8 (DRVL − GND).
HSGATE
η
is the highest switching frequency.
≈
P
∆
+
MAX
Q
T
and R
and Q
Q
HSGATE
JA
≈
HSGATE
is ADP3419’s thermal resistance from junction to air,
≈
θ
Q
Q
VCC
JA
HSGATE
LSGATE
LSGATE
LSGATE
+
×
+
Q
P
Q
×
MAX
LSGATE
are gate resistances of high-side and low-side
MAX
are the total gate charge of high-side and
LSGATE
(
Q
HSGATE
×
is 300 kHz, P
η
×
×
⎛
⎜
⎝
⎛
⎜
⎝
R1
HSGATE
R3
+
+
Q
0
+
0
HSGATE
5 .
R
LSGATE
5 .
R
HSGATE
×
= 18.6 nC and Q
×
LSGATE
R3
MAX
R1
= R
)
×
+
would be about
+
LSGATE
R
f
MAX
R4
+
0
R2
+
5 .
= 0.5, Equation 5
R
0
×
+
LSGATE
5 .
R4
R
ADP3419
LSGATE
×
HSGATE
R2
⎞
⎟
⎠
=
⎞
⎟
⎠
(3)
(4)
(5)