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| 型号： | LTC3448EMS8E |
| 厂商： | Linear Technology |
| 文件页数： | 9/20页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC ADJ 0.6A 8MSOP |
| 标准包装： | 50 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 0.6 V ~ 5.2 V |
| 输入电压： | 2.5 V ~ 5.5 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 1.5MHz ~ 2.25MHz |
| 电流 - 输出： | 600mA |
| 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-TSSOP，8-MSOP（0.118"，3.00mm 宽）裸露焊盘 |
| 包装： | 管件 |
| 供应商设备封装： | 8-MSOP-EP |
LTC3448
OPERATIO
1200
(Refer to Functional Diagram)
(see Typical Performance Characteristics). Therefore, the
1000
800
600
400
200
V OUT = 1.8V
V OUT = 1.5V
V OUT = 2.5V
user should calculate the power dissipation when the
LTC3448 is used at 100% duty cycle with low input voltage
(See Thermal Considerations in the Applications Informa-
tion section).
Low Supply Operation
The LTC3448 will operate with input supply voltages as
low as 2.5V, but the maximum allowable output current is
0
2.5
3.0
3.5 4.0 4.5
SUPPLY VOLTAGE (V)
5.0
5.5
reduced at this low voltage. Figure 4 shows the reduction
in the maximum output current as a function of input
3448 F04
Figure 4. Maximum Output Current vs Input Voltage
Dropout Operation
As the input supply voltage decreases to a value approach-
ing the output voltage, the duty cycle increases toward the
maximum on-time. Further reduction of the supply voltage
forces the main switch to remain on for more than one cycle
until it reaches 100% duty cycle. The output voltage will then
be determined by the input voltage minus the voltage drop
across the P-channel MOSFET and the inductor.
An important detail to remember is that at low input supply
voltages, the R DS(ON) of the P-channel switch increases
APPLICATIO S I FOR ATIO
voltage for various output voltages.
Slope Compensation and Inductor Peak Current
Slope compensation provides stability in constant fre-
quency architectures by preventing sub-harmonic oscilla-
tions at high duty cycles. It is accomplished internally by
adding a compensating ramp to the inductor current
signal at duty cycles in excess of 40%. This normally
results in a reduction of maximum inductor peak current
for duty cycles >40%. However, the LTC3448 uses a
patent-pending scheme that counteracts this compensat-
ing ramp, which allows the maximum inductor peak
current to remain unaffected throughout all duty cycles.
( )( )
V OUT ? 1 ? OUT ?
ThebasicLTC3448applicationcircuitisshownonthefirst
page of this data sheet. External component selection is
driven by the load requirement and begins with the selec-
tion of L followed by C IN and C OUT .
? I L =
1
f L
? V ?
? V IN ?
(1)
Inductor Selection
For most applications, the value of the inductor will fall in
the range of 1 μ H to 4.7 μ H. Its value is chosen based on the
desired ripple current. Large value inductors lower ripple
current and small value inductors result in higher ripple
currents. Higher V IN or V OUT also increases the ripple
current as shown in equation 1. A reasonable starting point
for setting ripple current is ? I L = 240mA (40% of 600mA).
The DC current rating of the inductor should be at least
equal to the maximum load current plus half the ripple
current to prevent core saturation. Thus, a 720mA rated
inductor should be enough for most applications (600mA
+ 120mA). For better efficiency, choose a low DC-resis-
tance inductor.
If the LTC3448 is to be used in auto LDO mode, inductor
values less than 1 μ H should not be used.
3448f
9
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