参数资料
| 型号： | LA5757TP-TL-E |
| 厂商： | ON Semiconductor |
| 文件页数： | 4/6页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ TP5HFA |
| 标准包装： | 700 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 可调至 1.255V |
| 输入电压： | 4.5 V ~ 32 V |
| 频率 - 开关： | 300kHz |
| 同步整流器： | 无 |
| 工作温度： | -30°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | TO-252-5，DPak（4 引线 + 接片），TO-252AD |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | TP5HFA |
LA5757TP
2. Start delay function
The SS pin has the internally-connected 10 μ A (typ) constant-current supply. When the voltage of SS pin exceeds
the threshold voltage, the regulator starts operation. As the threshold is 0.62V(typ), the start delay time can be
calculated as follows:
ex. For setting at 1 μ F
Td =
C × V
i
=
1 μ × 0.62
22 μ
= 28.2 msec
VOUT + VF
VIN - Vsat + VF
3. Soft start function
The internal PWM waveform has the voltage value as shown in the right.
If down-conversion from the voltage of VIN = 15V to 3.3V output to be made,
for example, the PWM-ON duty has the value as shown below.
PWMduty = = 25%
1.5V
0.62V
PWM wave
(Note that calculation is made with Vsat = 1V and VF = 0.2V)
The output voltage of error amplifier, which is 3.3V, is the value with PWM = 25%, as calculated in the above
equation, so that this voltage is determined as follows:
Ver = ( Δ VPWM) × PWMduty + VPWML = 0.88V × 0.25 + 0.62V = 0.84V
( Δ VPWM is the PWM amplitude value or 0.88V(typ) while VPWML is the lower limit voltage of PWM
waveform or 0.62V(typ))
SS pin and error amplifier output voltages are designed to prefer the lower voltages, so that VOUT will reach the
designed regulation voltage in timing when the SS pin voltage exceeds the error amplifier output. Therefore, the soft
strt time is calculated as follows:
Tss =
C × Δ VPWM × PWMduty
i
=
C × 0.88 × PWMduty
22 μ A
For the set conditions of C = 1 μ F and PWMduty = 25%:
Tss =
1 μ × 0.88V × 0.25
22 μ A
= 10msec
No.A1439-4/6
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