AAT4901 Datasheet, PDF (10/16 Pages) Advanced Analogic Technologies – Buffered Power Full-Bridge

FastSwitch^TM
The relationship between C_G(MAX) , Q_G(MAX) , and V_GATE is
given by:
Eq.
5:
C_G(MAX)
=
Q_G(MAX)
V_GATE
The peak current drive requirements for a given MOSFET
gate voltage can be derived from Equations 4 and 5:
Eq.
6:
I_G(MAX)
= ^QG(MAX)
dt
Design Example
V_IN = 5V
V_GATE = 5V
F_SW = 1MHz
θ_JA = 225°C/W
I_QAC = 4.0mA
T_J(MAX) = 120°C
T_A = 85°C
t_RISE = dt = 10ns
Q_G(MAX)
=
2
·
1
1MHz
·
⎛ 120°C - 85°C
⎝_{225°C/W · 5V}
- 4.0mA^⎞⎠
= 13.6nC
C_G(MAX)
=
Q_G(MAX)
V_GATE
=
13.6nC
5V
=
2.7nF
I_G(MAX)
=
Q_G(MAX)
dt
13.6nC
=
10ns
=
1.36A
PRODUCT DATASHEET
AAT4901
Buffered Power Full-Bridge
Typical Applications
2-Phase Synchronous Buck Converter
The most common AAT4901 applications include multi-
phase DC/DC converter output power stages, DC motor
drive, a dual low-side MOSFET driver, and a 3-state high-
speed high-current line driver.
Figure 2 shows a typical configuration when used as a
2-phase buck converter power stage with synchronous
rectification. The EN pin can be used to force outputs
OUTA/OUTB to a high impedance state; this allows the
output inductor to operate in discontinuous condition
mode (DCM) and improves efficiency under light load
conditions. The body diode associated with the low-side
switching device gives the AAT4901 inductive switching
capability, and clamps the LX node at one diode drop
below GND during the break-before-make time. The
multiphase buck converter assures a stable, high-perfor-
mance topology for high currents and low voltages which
are demanded in computers, workstation, telecom and
datacom servers. Figure 3 illustrates output ripple cur-
rent reduction due to 2-phase cancellation.
Motor Drive
The AAT4901 is ideally suited for use as an efficient out-
put driver for DC brushless motor control due to its full
bridge output stage with integrated MOSFETs. The induc-
tive load switching capability of the AAT4901 eliminates
the need for external diodes during commutation time.
In applications where rotation is always in the same
direction, a single half-bridge AAT4900 can be used to
drive a DC motor. If needed to control the rotation in
both directions, full-bridge motor control circuits can be
applied as shown in Figure 4. In this configuration the
motor can be controlled to run clockwise, counter-clock-
wise, stop rapidly (“regeneration” braking) or free run
(coast) to a stop.
10
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4901.2008.03.1.0