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参数资料
| 型号： | AS1337B-BTDT |
| 厂商： | ams |
| 文件页数： | 9/16页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK BOOST SYNC ADJ 8TDFN |
| 标准包装： | 1 |
| 类型： | 降压（降压），升压（升压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 2.5 V ~ 5 V |
| 输入电压： | 0.65 V ~ 4.5 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 1.2MHz |
| 电流 - 输出： | 200mA |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-WDFN 裸露焊盘 |
| 包装： | 标准包装 |
| 供应商设备封装： | 8-TDFN（3x3） |
| 其它名称： | AS1337B-BTDTDKR |
AS1337
Datasheet - D e t a i l e d D e s c r i p t i o n
Low-Voltage Start-Up and Soft Start
The AS1337 requires a V IN of only 0.85V (typ) or higher to start up. The low-voltage start-up circuitry controls the internal switches and provides
a soft start function, where the inductor current during start up is limited for a certain time. This soft start and in rush current limitation feature pro-
vides also a smooth curve of V OUT after start up and makes the overshoot of V OUT minimal. To achieve this, a 100pF capacitor as C FF is
needed (see Figure 13 on page 7) to speed up the feedback loop.
After a certain time a bigger inductor current is allowed and the soft start is disabled.
Low-Noise Fixed-Frequency Operation
Oscillator
The AS1337 switching frequency is internally fixed at 1.2MHz allowing the use of very small external components.
Current Sensing
A signal representing the internal NMOS-switch current is summed with the slope compensator. The summed signal is compared to the error
amplifier output to provide a peak current control command for the PWM. Peak switch current is limited to approximately 850mA independent of
V IN or V OUT .
Zero Current Comparator
The zero current comparator monitors the inductor current to the output and shuts off the PMOS synchronous rectifier once this current drops to
20mA (approx.). This prevents the inductor current from reversing polarity and results in improved converter efficiency at light loads.
Anti-Ringing Control
Anti-ringing control circuitry prevents high-frequency ringing on pin LX as the inductor current approaches zero. This is accomplished by damp-
ing the resonant circuit formed by the inductor and the capacitance on pin LX.
Setting Output Voltage
A voltage divider from VOUT to GND programs the output voltage from 2.5V to 5V via pin FB as:
V OUT = 1.23V(1 + (R 1 /R 2 ))
(EQ 1)
Powersave Operation
In light load conditions, the integrated powersave feature removes power from all circuitry not required to monitor V OUT . When V OUT has
dropped approximately 1% from nominal, the AS1337 powers up and begins normal PWM operation.
C OUT (see Figure 13 on page 7) recharges, causing the AS1337 to re-enter powersave mode as long as the output load remains below the pow-
ersave threshold. The frequency of this intermittent PWM is proportional to load current; i.e., as the load current drops further below the power-
save threshold, the AS1337 turns on less frequently. When the load current increases above the powersave threshold, the AS1337 will resume
continuous, seamless PWM operation.
Note: An optional capacitor (C FF ) between pins VOUT and FB in some applications can reduce V OUTp-p ripple and input quiescent current
during powersave mode. Typical values for C FF range from 15pF to 220pF.
Buck Mode
Both devices, the AS1337A and the AS1337B, offer a low power buck mode for V IN > V OUT operation. The switching during buck mode is simi-
lar to boost mode, but with forced reduction of some energy internal to be able to provide a buck conversion.
Shutdown
When pin EN is low the AS1337 is switched off and <1μA current is drawn from battery; when pin EN is high the device is switched on. If EN is
driven from a logic-level output, the logic high-level (on) should be referenced to V OUT to avoid intermittently switching the device on.
Note: If pin EN is not used, it should be connected directly to pin VOUT.
Caution: Because of the feedthrough the output voltage is the same as the input voltage during shutdown. If V IN >
V OUT the output voltage will jump to the value of the input voltage when the device switches into shutdown.
During normal operation the device is in down conversion mode.
Revision 1.05
8 - 15
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