a8450 Allegro MicroSystems, Inc., a8450 Datasheet - Page 7

• Manufacturer Part Number: a8450
• Description: Automotive Multioutput Voltage Regulator
• Manufacturer: Allegro MicroSystems, Inc.

Buck Converter with Switching Regulator. A cur-
rent-mode, variable frequency buck dc-to-dc converter and
switching regulator are integrated in the A8450, as shown in
figure 2. This feature allows the device to efficiently handle
power over a wide range of input supply levels. The dc-to-dc
converter outputs 5.7 V typical, and has an overcurrent limit
of 1.2 A typical.
The converter employs a soft-start feature. This ramps the
converter output voltage and limits the maximum demand on
V
to charge the external capacitor, COUT, and any dc load.
An internal charge pump provides gate drive for the
N-channel MOSFET buck switch. A 100% duty cycle is
implemented when using low V
At V
in figure 3. This reduction keeps the switching frequency,
f
rent. Lowering the ripple current at low V
degradation of linear regulator headroom due to V
voltage.
5 V Linear Regulators. Two 5 V medium-power linear regula-
tors are provided. These low-dropout regulators feature foldback
current limiting for short-to-supply protection. When a direct
A8450KLB-DS, Rev. 2
PWM
REG
BB
, within a reasonable range and lowers the ripple cur-
by controlling the inrush current required at power-on
lower than 12 V, off-time, t
ENB
VCP
BB
Buck Converter
Generation
Soft Start
Bandgap
Counter
1.22 V
Ramp
Clock
input voltages.
OFF
, is reduced, as shown
Figure 2. Buck converter with switching regulator
BB
levels prevents
Functional Description
VBB
REG
Automotive Multioutput Voltage Regulator
ripple
1.2 A Limit
Error
Clamp
Switching
Regulator
Control
I
DEMAND
I
PEAK
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Compensation
Buck Switch
5
Figure 3. When VBB falls below 12 V, t
LX
t
OFF
0.58 μs
6.02 V
D1
7
100 μH
L1
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com
t
9
OFF
V
BB
by V
VREG
(V)
100 μF
COUT
BB
11
2.05 μs
11 V
OFF
4.75 μs
12 V
13
A8450
decreases
15
7