ADP3419

Rev. A | Page 11 of 16

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

Part Number

Web Address

Murata

GRM235Y5V106Z16

www.murata.com

Taiyo-Yuden

EMK325F106ZF

www.t-yuden.com

Tokin

C23Y5V1C106ZP

www.tokin.com

Keep the ceramic capacitor as close as possible to the ADP3419.

BOOTSTRAP CIRCUIT

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

BST

HSGATE

BST

V

Q

C

∆

=

(1)

where:

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

(2)

MAX

HSGATE

AVG

F

f

Q

I

×

=

)

(

where

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

MAX

LSGATE

HSGATE

MAX

f

Q

Q

VCC

P

×

+

×

≈

)

(

(3)

where:

VCC is the supply voltage 5 V.

low-side MOSFETs, respectively.

For example, the ADP3419 drives two IRF7821 high-side

MOSFETs and two IRF7832 low-side MOSFETs. According to

130 mW.

Part of this power consumption generates heat inside the

ADP3419. The temperature rise of the ADP3419 against its

environment is estimated as

η

×

×

θ

≈

∆

MAX

JA

P

T

(4)

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

LSGATE

LSGATE

LSGATE

HSGATE

LSGATE

HSGATE

HSGATE

LSGATE

HSGATE

HSGATE

R

R4

R4

R

R3

R3

Q

Q

Q

R

R2

R2

R

R

R1

R1

Q

Q

Q

5

.

0

5

.

0

5

.

0

5

.

0

(5)

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.

MOSFETs, respectively.

gives a value of η = 0.71. Based on Equation 4, the estimated

temperature rise in this example is about 22°C.