参数资料
| 型号： | A8670EESTR-T |
| 厂商： | Allegro Microsystems Inc |
| 文件页数： | 12/28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 |
第1页第2页第3页第4页第5页第6页第7页第8页第9页第10页第11页当前第12页第13页第14页第15页第16页第17页第18页第19页第20页第21页第22页第23页第24页第25页第26页第27页第28页
A8670
Fixed Frequency, 2 A Synchronous Buck Regulator
With Fault Warnings and Power OK
When selecting larger-value output capacitors, it is important that
the soft-start period is appropriately scaled to take into account
the charging of these capacitors. For example, if the soft-start is
optimized for a 22 μ F ceramic output capacitor and a 2000 μ F
capacitor is added to the output, there is every possibility that the
converter will remain in an overload condition after the soft-start
and the Hiccup Overload Duration have elapsed. This mode of
operation could prevent the output ever reaching the target output
voltage.
To demonstrate the above, consider the following example: a
regulator programmed for a 5 V output, 20 μ F output capacitor,
and a soft-start time-off of 1 ms.
Assume there is no load current draw until 5 V is reached. At
start-up, the regulator has to charge the output capacitor. From
C×V = I×t , the charging current into the capacitor is:
I = 20 μ F × 5 / 1 ms = 100 mA
Now if a 2000 μ F capacitor is added to the output, the capacitor
would require a charge current of:
I = 2000 μ F × 5 / 1 ms = 10 A
In this condition, the A8670 would run into the pulse-by-pulse
current limit, limiting the average charge current to 2.9 A (typ).
An average current of 2.9 A, assumes a valley current limit of
2.7 A and a half ripple current of 0.2 A. This means that after the
soft-start delay of 1 ms, the output voltage would only be charged
to:
V = 2.9 A × 1 ms / 2000 μ F = 1.45 V
After the soft-start period is completed, the output capacitor
would be charged for a short duration, defined by the Hiccup
Overload Duration. Then the converter would shut down and,
after the Hiccup Shutdown Duration had elapsed, would enter
the start-up process again. This mode is highly undesirable and a
more appropriate soft-start capacitor should be selected.
The effects of adding an output capacitor with too-large value
would be a condition similar to starting-up into a short-circuit
across the output; where the regulator enters a hiccup mode of
operation.
If the output of the A8670 is pre-biased at start-up, the switcher
will remain in a high impedance state until the soft-start has
reached the feedback voltage ( V FB ) amplitude. This avoids the
output voltage being discharged. After the soft-start threshold
exceeds the FB pin voltage, PWM switching action occurs and
the output voltage is brought up under the control of the soft-start
circuit (see figure 2).
Note that when the regulator is turned off, it enters a high
impedance mode (all switches off) and if the output voltage is
discharged it is done so by the load (at A in figure 2). If the load
does not discharge the output, the output voltage remains in a
pre-biased condition.
Fault Handling and Reporting
Table 3 describes the action taken for particular faults including
the status of the ˉF ˉAˉ ˉUˉ ˉLˉ ˉTˉ and POK flags.
Enable (EN)
0V
Soft-Start/ Hiccup (SS)
0V
Soft-Start Ramp Time
Target output voltage
90% of
Target
Pre-biased output voltage
Output Voltage
0V
Soft-start voltage
less than feedback
voltage (V FB )
No PWM switching
Feedback voltage (V FB )
brought-up under
soft-start control
PWM switching
90 μ s
POK Delay
A
Load pulls
the output
voltage low
Power OK (POK)
0V
Figure 2. Operation of the soft-start function with pre-biasing
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
11
相关PDF资料 |
PDF描述 |
|---|---|
| A8697ELJ-T | IC REG BUCK ADJ 4A 8SOIC |
| A8698ELJ-T | IC REG BUCK ADJ 3A 8SOIC |
| A8732EEETR-T | IC PHOTOFLASH CAP CHARGER 8DFN |
| A8735EEETR-T | IC PHOTOFLASH CAP CHARGER 8DFN |
| A8739EEETR-T | IC PHOTOFLASH CHARGER 8-DFN |
相关代理商/技术参数 |
参数描述 |
|---|---|
| A86724-000 | 制造商:TE Connectivity 功能描述:CMC-0587-00-9CS2968 - Cable Rools/Shrink Tubing |
| A-869 | 制造商:ETC MOLEX-INACTIVE 功能描述:Cross Referenced to MOLEX - Part: MOL19036-0003 |
| A86953-000 | 制造商:TE Connectivity 功能描述:Data Bus Components A Wide Selection Of Couplers Such As Micros, Boxes, Flat-Packs, And Ultra Light Weight Versions 制造商:TE Connectivity 功能描述:DATABUS HARNESSES - Bulk 制造商:TE Connectivity 功能描述:D-500-0467-2-612-012 |
| A8697 | 制造商:ALLEGRO 制造商全称:Allegro MicroSystems 功能描述:Wide Input Voltage 4.0 A Step Down Regulator |
| A86976-000 | 功能描述:可复位保险丝 RoHS:否 制造商:TE Connectivity / Raychem 电流额定值: 电阻:0.08 Ohms (max) 最大直流电压: 保持电流:2.5 A 安装风格:Through Hole 端接类型: 跳闸电流:5 A 引线间隔: 系列:RXEF 工作温度范围:+ 85 C |
发布紧急采购，3分钟左右您将得到回复。