ADP3419 查看數據表（PDF） - Analog Devices
零件编号
产品描述 (功能)
比赛名单
ADP3419 Datasheet PDF : 16 Pages
| |||
ADP3419
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
Part Number
GRM235Y5V106Z16
EMK325F106ZF
C23Y5V1C106ZP
Web Address
www.murata.com
www.t-yuden.com
www.tokin.com
Keep the ceramic capacitor as close as possible to the ADP3419.
BOOTSTRAP CIRCUIT
The bootstrap circuit uses a charge storage capacitor (CBST) and
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
C BST
= Q HSGATE
∆VBST
(1)
where:
QHSGATE is the total gate charge of the high-side MOSFET.
∆VBST is the voltage droop allowed on the high-side MOSFET
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
IF(AVG) = QHSGATE × fMAX
(2)
where fMAX is the maximum switching frequency of the
controller.
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
PMAX ≈ VCC × (QHSGATE + QLSGATE )× f MAX
(3)
where:
VCC is the supply voltage 5 V.
fMAX is the highest switching frequency.
QHSGATE and QLSGATE are the total gate charge of high-side and
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, QHSGATE = 18.6 nC and QLSGATE =
68 nC. Given that fMAX is 300 kHz, PMAX would be about
130 mW.
Part of this power consumption generates heat inside the
ADP3419. The temperature rise of the ADP3419 against its
environment is estimated as
∆T ≈ θ JA × PMAX × η
(4)
where θJA is ADP3419’s thermal resistance from junction to air,
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
η
≈
QHSGATE
QHSGATE + QLSGATE
× ⎜⎛
⎝
0.5 × R1
R1 + RHSGATE
+R
+
0.5 × R2
R2 + RHSGATE
⎟⎞
⎠
(5)
+
Q LSGATE
QHSGATE + QLSGATE
×
⎜⎛
⎝
0.5 × R3
R3 + RLSGATE
+
0.5 × R4
R4 + RLSGATE
⎟⎞
⎠
where:
R1 and R2 are the output resistances of the high-side driver:
R1 = 1.7 (DRVH − BST), R2 = 0.8 (DRVH − SW).
R3 and R4 are the output resistances of the low-side driver:
R3 = 1.7 (DRVL − VCC), R4 = 0.8 (DRVL − GND).
R is the external resistor between the BST pin and the BST
capacitor.
RHSGATE and RLSGATE are gate resistances of high-side and low-side
MOSFETs, respectively.
Assuming that R = 0 and that RHSGATE = RLSGATE = 0.5, Equation 5
gives a value of η = 0.71. Based on Equation 4, the estimated
temperature rise in this example is about 22°C.
Rev. A | Page 11 of 16
Share Link: 