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參數(shù)資料
| 型號(hào)： | A8450KLBTR-T |
| 廠商： | Allegro Microsystems Inc |
| 文件頁(yè)數(shù)： | 11/17頁(yè) |
| 文件大?。?/td> | 546K |
| 描述： | IC REG QD BUCK/LINEAR 24-SOIC |
| 標(biāo)準(zhǔn)包裝： | 3,000 |
| 拓?fù)洌?/td> | 降壓（降壓）（1），線(xiàn)性（LDO）（4） |
| 功能： | 車(chē)載 |
| 輸出數(shù)： | 4 |
| 電壓/電流 - 輸出 1： | 5.7V，1.2A |
| 電壓/電流 - 輸出 2： | 5V，200mA |
| 電壓/電流 - 輸出 3： | 5V，200mA |
| 帶 LED 驅(qū)動(dòng)器： | 無(wú) |
| 帶監(jiān)控器： | 無(wú) |
| 帶序列發(fā)生器： | 是 |
| 電源電壓： | 6 V ~ 45 V |
| 工作溫度： | -40°C ~ 135°C |
| 安裝類(lèi)型： | 表面貼裝 |
| 封裝/外殼： | 24-SOIC（0.295"，7.50mm 寬） |
| 供應(yīng)商設(shè)備封裝： | 24-SOIC W |
| 包裝： | 帶卷 (TR) |
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Automotive Multioutput Voltage Regulator
A8450
11
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Component Selection
Output Inductor (L1). This inductor must be rated to handle the
total load current, I
LOAD
. In addition, the value chosen must keep
the ripple current to a reasonable level. A typical selection is a
power inductor rated at 100 糎 and 1.3 A.
The worse case ripple current, I
RIPPLE(max)
(mA), can be calcu-
lated as
I
RIPPLE(max)
= V
L1OFF
?SPAN class="pst A8450KLBTR-T_2464169_10">
t
OFF
D L
L1
where L
L1
(糎) is the inductance for the selected component, and
V
L1OFF
is the voltage (V) through the inductor when the A8450 is
in the quiescent state
V
L1OFF
= V
REG(max)
+ V
D1
+ (I
LOAD ?/SPAN>
R
L1
)
where V
D1
(V) is the voltage drop on diode D1, I
LOAD
(mA) is
the total load current, and R
L1
is the specified DC resistence (?
for the selected inductor at its rated temperature.
The frequency, f
PWM
(Hz), of the switching regulator in the buck
converter can then be estimated by
f
PWM
= 1/(t
ON
+ t
OFF
)
where t
ON
(約) is calculated as
t
ON
= I
RIPPLE(max)
?SPAN class="pst A8450KLBTR-T_2464169_2">
L
L1
D V
L1ON
and V
L1ON
(V) as
V
L1ON
= V
BB
(I
LOAD
?SPAN class="pst A8450KLBTR-T_2464169_2">
R
DSON(max)
)
(I
LOAD ?/SPAN>
R
L1
) V
REG(max)
Example
Given a typical application with V
BB
= 14 V, t
OFF
= 4.75 約, and
I
LOAD
= 550 mA. (Note that the value for t
OFF
is constant for V
BB
> 12 V, as shown in figure 3.)
Given also a 100 糎 power inductor rated at 400 m?for 125篊.
(Note that temperature ratings for inductors may include self-
heating effects. If a 125篊 rating includes a self-heating tempera-
ture rise of 20篊 at maximum current, then the actual ambient
temperature, T
A
, cannot exceed 105篊.)
V
L1OFF
= 5.8 + 0.8 + (0.550
?
0.400) = 6.821 V
I
RIPPLE(max)
= 6.821
?/DIV>
4.75 D 100 = 0.324 A
V
L1ON
= 14 (0.550
?/DIV>
0.750) (0.550
?/DIV>
0.400)
5.8 = 7.56 V
t
ON
= 0.324
?/DIV>
100 D 7.56 = 4.3 約
f
PWM
= 1/(4.3 + 4.75) = 111 kHz
In the case of a shorted output, the buck converter could reach
its internal current limit, I
DSLIM
, of 1.2 A typical. To ensure safe
operation, the I
SAT
rating for the selected inductor should be
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
LOAD
,
could never reach that internal current limit, then an inductor can
be selected that has an I
SAT
rating closer to the calculated output
current of the device, I
LOAD
, plus the maximum ripple current,
I
RIPPLE(max)
.
Higher inductor values can be chosen to lower I
RIPPLE
. This may
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
LOAD
(mA), is calculated as
I
LOAD
= I
DSLIM
(I
RIPPLE(max)
D 2)
Catch Diode (D1). The Schottky catch diode should be rated to
handle 1.2 times the maximum load current, I
LOAD
, because the
duty cycle at low input voltages, V
BB
, can be very close to 100%.
The voltage rating should be higher than the maximum input
voltage, V
BB(max)
, expected during any operating condition.
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
RIPPLE(p-p)
(mV), is calculated as
V
RIPPLE(p-p)
= I
RIPPLE
?SPAN class="pst A8450KLBTR-T_2464169_10">
ESR
COUT
with ESR in ohms. It is recommended that the maximum level of
V
RIPPLE(p-p)
be less than 200 mV.
For electrolytic output capacitors, a low-ESR type is recom-
Application Information
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