参数资料
| 型号： | A8670EESTR-T |
| 厂商： | Allegro Microsystems Inc |
| 文件页数： | 10/28页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 2A 20QFN |
| 标准包装： | 1 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 可调至 0.6V |
| 输入电压： | 7 V ~ 16 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 200kHz ~ 1MHz |
| 电流 - 输出： | 2A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 20-WFQFN 裸露焊盘 |
| 包装： | 标准包装 |
| 供应商设备封装： | 20-QFN 裸露焊盘（4x4） |
| 其它名称： | 620-1397-6 |
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A8670
Fixed Frequency, 2 A Synchronous Buck Regulator
With Fault Warnings and Power OK
Table 2 provides preferred inductor values for a given output
voltage, 2 A output at target switching frequencies of 500 kHz,
700 kHz, and 1 MHz.
When using ceramic capacitors, it is important to consider the
effects of capacitance reduction due to the E-field. To avoid this
voltage bias effect, it is recommended that the capacitor rated
Table 2. Recommended Inductor Values
Switching Frequency, f SW
500 kHz 700 kHz 1 MHz
V OUT L V OUT L V OUT
(V) ( μ H) (V) ( μ H) (V)
L
( μ H)
voltage be at least twice that of the actual output voltage. So for
example, with a 5 V output, the capacitor should be rated to 10 V.
For the majority of applications, a 20 μ F output capacitor is
recommended.
5.0
3.3
2.5
1.8
1.5
1.2
1.0
0.8
0.6
10
10
10
6.8
4.7
4.7
3.6
3.6
2
5.0
3.3
2.5
1.8
1.5
1.2
1.0
0.8
0.6
10
6.8
4.7
4.7
3.6
3.6
2
2
1.4
5.0
3.3
2.5
1.8
1.5
1.2
1.0
0.8
0.6
6.8
4.7
3.6
3.6
3.6
2
2
1.4
0.9
Input Capacitor Selection
The function of the input capacitor is to provide a low impedance
shunt path for the current drawn by the A8670 when the high-
side switch is on. This minimizes the amount of ripple current
reflected back into the source supply. This reduces the potential
for higher conducted electromagnetic interference (EMI).
In a correctly designed system, with a quality capacitor posi-
tioned adjacent to the VIN pin and the PGND pin, this capacitor
should supply the high-side switch current minus the average
input current. During the high-side switch off-cycle, the capacitor
is charged by the average input current.
1 /
V OUT I OUT
V IN
Output Capacitor Selection
The output capacitor has two main functions: influence the con-
trol loop response (see the Control Loop section), and determine
the magnitude of the output voltage ripple.
The output voltage ripple can be approximated to:
The effective rms current that flows in the input filter capaci-
tor is:
2
I rms = –1
V IN V OUT
(10)
where:
V ripp =
8
I ripp
f SW C OUT
(9)
The amount of ripple voltage (V ripp ) that appears across the
input terminals (VIN with respect to GND) is determined by the
amount of charge removed from the input capacitor during the
high-side switch conduction time. If a capacitor technology such
C IN =
I ripp is the peak-to-peak current in the inductor (see the Inductor
Selection section), and
C OUT is the output capacitance.
It is recommended that ceramic capacitors be used, taking into
account: size, cost, reliability, and performance. It is imperative
that ceramic type X5R or X7R are used. On no account should
Y5V, Y5U, Z5U, or similar be used, because the capacitance
tolerance and the temperature stability is very poor.
There is generally no need to consider the effects of heating
caused by the ripple current flowing into the output capacitor.
This is because the equivalent series resistance (ESR) of ceramic
capacitors is extremely low.
as an electrolytic is used, then the effects of the ESR should also
be taken into account.
The amount of input capacitance (C IN ) required for a given ripple
voltage can be found:
I rms t on (11)
V ripp
where:
t on is the on-time of the high-side switch (see the Switch On-
Time and Switching Frequency section; note that maximum ton
occurs at minimum input voltage), and
CIN is the input filter capacitance.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
9
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