AAT4901IJS-1-T1 ANALOGICTECH [Advanced Analogic Technologies], AAT4901IJS-1-T1 Datasheet - Page 9

• Manufacturer Part Number: AAT4901IJS-1-T1
• Description: Buffered Power Full-Bridge
• Manufacturer: ANALOGICTECH [Advanced Analogic Technologies]

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Application Information
Input Supply Capacitor
The input capacitor provides a low impedance loop for
the edges of pulsed current drawn by the AAT4901 and
reduces the surge current drawn from the input power.
A 4.7μF to 10μF X7R or X5R low ESR/ESL ceramic capac-
itor is selected for the input supply decoupling. To mini-
mize the tray resistance, the capacitor should be placed
as closely as possible to the input pin. This keeps the
high frequency content of input current localized, mini-
mizing EMI and input voltage ripple.
Shoot-Through Protection
The internal high-side and low-side MOSFETs of the
AAT4901 cannot conduct at the same time to prevent
shoot-through current. When the high-side MOSFET
turns on, the low-side MOSFET turns off first; after 5ns
break-before-make time, the high-side MOSFET then
turns on. Similarly, before the low-side MOSFET turns
on, the high-side MOSFET turns off; after a certain
break-before-make time (5ns typ.), the low-side MOSFET
turns on. The dead time between the high-side and low-
side turn-on should be kept as low as possible to mini-
mize current flows through the body diode of the high-
side and/or low-side MOSFET(s). The break-before-make
shoot-through protection significantly reduces losses
associated with the driver at high frequency.
Thermal Calculations
In the dual low-side MOSFET driver application, the
power dissipation of the AAT4901 includes the power
dissipation in the MOSFETs due to charging and dis-
charging the gate capacitance, the AC quiescent current
power dissipation, and transient power in the driver dur-
ing output transitions. As the transient power is usually
very small, its losses can be ignored. Maximum package
power dissipation can be estimated by the following
equation:
Eq. 1:
4901.2008.03.1.0
P
D(MAX)
= V
= I
TM
QAC
CC
· I
· V
IN
CC
=
+ Q
T
J(MAX)
G(tot)
θ
JA
F
- T
SW
A
· V
CC
w w w . a n a l o g i c t e c h . c o m
Where:
T
T
θ
I
Q
F
The maximum junction temperature for the SC70JW-8
package can be derived from Equation 1:
Eq. 2:
For example, if the AAT4901 drives 2 AAT9560 MOSFETs
whose maximum gate charge is specified as 13nC for
V
switching frequency of 1MHz equals:
Gate Drive Current Ratings
Assuming that the maximum gate charge of the dual
low-side MOSFETs are equal, the maximum gate drive
capability for the designed maximum junction tempera-
ture without an external resistor can be derived from
Equation 1:
Eq. 3:
The relationship between gate capacitance, turn-on/
turn-off time, and the MOSFET driver current rating can
be determined by:
Eq. 4:
Where:
I
C
dV = MOSFET gate-to-source voltage
dt = rising time of MOSFET gate-to-source voltage
QAC
G(MAX)
A
SW
J(MAX)
JA
GATE
G(MAX)
G(tot)
P
(nC).
= ambient temperature (°C).
D(tot)
= thermal resistance (225°C/W).
= switching frequency (MHz).
= AC quiescent current of the driver (mA).
= 5V, the total power dissipation in the driver at a
= total gate charge of external low side MOSFETs
= junction temperature of the dice (°C).
= peak drive current for a given voltage
= maximum gate capacitance
T
= 2 · (5V · 13nC · 1MHz) + 5V · 4.0mA = 150mW
Q
I
G(MAX)
J(MAX)
G(MAX)
= C
= P
=
2 · F
G(MAX)
D(MAX)
1
Buffered Power Full-Bridge
SW
PRODUCT DATASHEET
·
· θ
dV
·
dt
JA
T
+ T
J(MAX)
θ
JA
A
· V
AAT4901
- T
IN
A
- I
QAC
9