A8450KLB Allegro Microsystems Inc, A8450KLB Datasheet - Page 11

• Manufacturer Part Number: A8450KLB
• Description: IC REG MULTI-OUT AUTO 24-SOIC
• Manufacturer: Allegro Microsystems Inc
• Type: Step-Down (Buck)r

Specifications of A8450KLB

• Topology: Step-Down (Buck) (1), Linear (LDO) (4)
• Function: Automotive
• Number Of Outputs: 4
• Voltage/current - Output 1: 5.7V, 1.2A
• Voltage/current - Output 2: 5V, 200mA
• Voltage/current - Output 3: 5V, 200mA
• W/led Driver: No
• W/supervisor: No
• W/sequencer: Yes
• Voltage - Supply: 6 V ~ 45 V
• Operating Temperature: -40°C ~ 135°C
• Mounting Type: Surface Mount
• Package / Case: 24-SOIC (7.5mm Width)
• Current - Output: 200mA, 550mA
• Voltage - Output: 3.3V, 5V, 5.7V, Adj
• Voltage - Input: 6 ~ 45 V
• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -
• Frequency - Switching: -

A8450
Component Selection
Output Inductor (L1).
total load current, I
the ripple current to a reasonable level. A typical selection is a
power inductor rated at 100 μH and 1.3 A.
The worse case ripple current, I
lated as
where L
V
in the quiescent state
where V
the total load current, and R
for the selected inductor at its rated temperature.
The frequency, f
converter can then be estimated by
where t
and V
Example
Given a typical application with V
I
> 12 V, as shown in figure 3.)
Given also a 100 μH power inductor rated at 400 mΩ for 125ºC.
(Note that temperature ratings for inductors may include self-
heating effects. If a 125ºC rating includes a self-heating tempera-
ture rise of 20ºC at maximum current, then the actual ambient
temperature, T
LOAD
L1OFF
L1ON
= 550 mA. (Note that the value for t
ON
is the voltage (V) through the inductor when the A8450 is
D1
L1
V
L1ON
(μs) is calculated as
(μH) is the inductance for the selected component, and
(V) as
V
(V) is the voltage drop on diode D1, I
L1OFF
A
I
= V
, cannot exceed 105ºC.)
RIPPLE(max)
PWM
t
ON
BB
LOAD
= V
= I
(Hz), of the switching regulator in the buck
– (I
f
REG(max)
PWM
This inductor must be rated to handle the
RIPPLE(max)
. In addition, the value chosen must keep
LOAD
= V
L1
= 1/(t
is the specified DC resistence (Ω)
×
L1OFF
RIPPLE(max)
+ V
R
ON
BB
DSON(max)
×
D1
+ t
×
L
= 14 V, t
+ (I
– (I
L1
OFF
t
OFF
LOAD
⁄ V
LOAD
OFF
(mA), can be calcu-
)
)
L1ON
⁄ L
OFF
is constant for V
×
×
L1
Automotive Multioutput Voltage Regulator
LOAD
R
Application Information
R
= 4.75 μs, and
L1
L1
)
) – V
(mA) is
REG(max)
BB
In the case of a shorted output, the buck converter could reach
its internal current limit, I
operation, the I
greater than 1.4 A. However, if the external current limit resistors,
R3 and R4, selected for the 3.3 V and adjustable (1.2 V to 3.3 V)
regulators, are rated such that the total inductor current, I
could never reach that internal current limit, then an inductor can
be selected that has an I
current of the device, I
I
Higher inductor values can be chosen to lower I
be an option if it is desired to increase the total maximum current
that is drawn from the switching regulator. The maximum total
current available, I
Catch Diode (D1). The Schottky catch diode should be rated to
handle 1.2 times the maximum load current, I
duty cycle at low input voltages, V
The voltage rating should be higher than the maximum input
voltage, V
VREG Output Capacitor (COUT). Voltage ripple in the
VREG output is the main consideration when selecting the
VREG output capacitor, COUT. The peak-to-peak output voltage
ripple, V
with ESR in ohms. It is recommended that the maximum level of
V
For electrolytic output capacitors, a low-ESR type is recom-
RIPPLE(max)
RIPPLE(p-p)
V
V
I
t
f
ON
RIPPLE(max)
L1ON
PWM
L1OFF
RIPPLE(p-p)
= 14 – (0.550
= 0.324
= 1/(4.3 + 4.75) = 111 kHz
BB(max)
= 5.8 + 0.8 + (0.550
.
be less than 200 mV.
SAT
= 6.821
I
V
LOAD
, expected during any operating condition.
RIPPLE(p-p)
×
LOAD
rating for the selected inductor should be
(mV), is calculated as
100 ⁄ 7.56 = 4.3 μs
= I
LOAD
×
SAT
×
(mA), is calculated as
DSLIM
DSLIM
4.75 ⁄ 100 = 0.324 A
0.750) – (0.550
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
rating closer to the calculated output
, plus the maximum ripple current,
= I
RIPPLE
×
, of 1.2 A typical. To ensure safe
– (I
0.400) = 6.821 V
BB
RIPPLE(max)
, can be very close to 100%.
×
ESR
×
0.400)
COUT
LOAD
⁄ 2)
RIPPLE
, because the
– 5.8 = 7.56 V
. This may
LOAD
,
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