参数资料
| 型号： | A4403GEUTR-T |
| 厂商： | Allegro Microsystems Inc |
| 文件页数： | 11/16页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 3A 16QFN |
| 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 0.8V |
| 输入电压： | 9 V ~ 46 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 450kHz ~ 2MHz |
| 电流 - 输出： | 3A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 105°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-WQFN 裸露焊盘 |
| 包装： | 标准包装 |
| 供应商设备封装： | 16-QFN（4x4） |
| 产品目录页面： | 1141 (CN2011-ZH PDF) |
| 其它名称： | 620-1273-6 |
A4403
Valley Current Mode Control Buck Converter
R FILTER and C FILTER (R7 and C7 in the Typical Application
diagram) should be placed close to the A4403 pins. The ground
Estimate the R DS(on) of the buck switch at the given junction
temperature:
T J – 25 ?
?
?
sense should connect directly to the SGND and not to the power
ground.
?
R DS(on)TJ = R DS(on)25C ? ? 1 +
?
170
?
.
(20)
Support Components The bootstrap capacitor (C2) and soft-
start capacitor (C5) should be ceramic X5R or X7R.
The static loss for each switch can be determined:
Thermal Considerations To ensure the A4403 operates in
the safe operating area, which effectively means restricting the
junction temperature to less than 150°C, several checks should be
made. The general approach is to work out what thermal imped-
ance, R ? JA , is required to maintain the junction temperature at
a given level, for a particular power dissipation. (Another factor
P STAT = I LOAD2 × D (max) × R DS(on)TJ ,
where I LOAD is the load.
(b) Switch dynamic losses
Both the turn-on and the turn-off losses can be estimated:
(21)
worth considering is that other power dissipating components
on the system PCB may influence the thermal performance of
P DYN = V IN (min) ×
I LOAD
2
× 5 × 10 –9 × f SW × 1.6
,
(22)
the A4403. For example, the power loss contribution from the
recirculation diode and the sense resistor may cause the junction
temperature of the A4403 to be higher than expected.) It should
be noted that this process is usually an iterative one to achieve the
optimum solution.
where f SW is the switching frequency.
(c) Diode capacitance turn-on loss
At turn-on, an additional current spike flows into the switch, caus-
ing a loss as follows:
The following steps can be used as a guideline for determining
the R ? JA for a suitable thermal solution. :
P DIODECAP =
C DIODE × V IN2 × f SW
2
,
(23)
1. Estimate the maximum ambient temperature, T A (max) , of the
application.
2. Define the maximum junction temperature, T J (max). Note that
the absolute maximum is 150°C.
3. Determine the worst case power dissipation, P D (max). This will
occur at maximum load and minimum V IN . Contributors are:
(a) Switch static losses
Estimate the maximum duty cycle:
where C DIODE is the body capacitance of the Schottky diode (D1).
(d) Control losses
The control losses can be estimated as follows:
P CTRL = I VINON × V IN , (24)
where I VINON is the quiescent current with the converter enabled.
(e) Gate charge losses
D (max) =
V OUT + V f
V IN (min) + V f
,
(19)
Estimate the charge losses as follows:
P GATE = Q × f SW × V IN ,
(25)
where V f is the forward voltage drop of the Schottky diode (D1)
and sense resistor (R2, R3) under the given load current.
where Q = 5 nC and is the charge that is required to turn on the
buck switch.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
11
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