参数资料
| 型号： | A4403GEUTR-T |
| 厂商： | Allegro Microsystems Inc |
| 文件页数： | 7/16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
Then, the minimum on-time is:
Valley Current Mode Control Buck Converter
Top-Off Charge Pump During light load operation, when
T on (min) = ? ?
?
? ×
? 5 + 0.5
46 + 0.5
?
?
?
1
1× 10 6
= 118 ns
operating in PFM mode, the top-off charge pump provides
enough charge to drive the buck switch.
Light Load Operation To avoid the output voltage peak charg-
? ?
T on = ? ?
? + 10 × 10 –9
.
× 2.05 × 10 10
? (5)
? IN
?
The specified minimum on-time,T on(min) , is 60 ns maximum, so
there is reasonable margin in this case.
The specified minimum off-time, T off(min) , 350 ns maximum,
also has to be considered. The minimum off-time occurs at
minimum input voltage and maximum load. As was shown in the
minimum on-time calculation (equation 4), you have to exam-
ine the extreme operating conditions to ensure adequate margin
exists.
The switch on-time, T on , is set by the current flowing into the
TON pin. The current is determined by the input voltage, V IN ,
and the resistor R1. The on-time can be found as:
R 1
V
The switching frequency may be slightly modulated by load
changes. The on-time is always constant for a given input voltage
and across the load range. To compensate for any losses in the
circuitry (for example, in the series switch and inductor, or in the
voltage drop across the recirculation diode), the off-time, hence
the switching frequency, has to be adjusted. This effect is most
noticeable at low input voltages and high output currents.
To calculate the actual switching frequency, the T on of equa-
tion 5 can be used in conjunction with the transfer function of the
ing due to leakage effects from the buck switch and the charge
pump recirculation current, a minimum load of 1 mA must be
applied to the output.
The output feedback resistor network provides some loading.
Depending on the values selected, this network may provide all,
or at least some, of the minimum loading requirement.
Control Loop The process of closing the control loop for the
A4403 has been greatly simplified through the integration of
the compensation components into the device. The control loop
bandwidth has been optimized for operation across the full input
and output voltage range and for switching frequencies between
450 kHz and 2 MHz. Loop optimization is achieved with a 20 μ F
ceramic capacitor placed across the output (VOUT to GND) and
a power inductor that achieves a peak to peak ripple current of
around 720 mA. For example, for a 3.3 V output operating at a
frequency of 1 MHz, the power inductor = 4.7 μ H.
Larger output capacitors can be used; however, this tends to
decrease the bandwidth of the control loop. Note that the output
capacitance should not exceed 1000 μ F or be less than 10 μ F, as
this may cause a loop instability to occur.
2000
1800
converter:
1600
V OUT
f SW = ? ?
?
? ×
? V OUT + V f
V IN + V f
?
?
?
1
T on
.
(6)
1400
1200
An alternative approach to selecting the TON resistor (R1), to
accomplish an approximate switching frequency is found in the
1000
800
0.8 V
1.5 V
3.3 V
5 V
12 V
following formula:
600
R 1 =
V OUT × 2.05 × 10 10
f SW
.
(7)
400
10
100
Resistor R1 (k Ω )
1000
Figure 2 illustrates a range of switching frequencies that can be
achieved with various TON resistances and output voltages.
Figure 2. Switching frequencies versus TON resistor values, at various
levels of V OUT
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
7
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