参数资料
| 型号： | LT1618EMS#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 7/16页 |
| 文件大小： | 0K |
| 描述： | IC REG BOOST ADJ 1.5A 10MSOP |
| 标准包装： | 2,500 |
| 类型： | 升压（升压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 1.26 V ~ 36 V |
| 输入电压： | 1.6 V ~ 18 V |
| PWM 型： | 电流/电压模式 |
| 频率 - 开关： | 1.4MHz |
| 电流 - 输出： | 1.5A |
| 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： | 10-TFSOP，10-MSOP（0.118"，3.00mm 宽） |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 10-MSOP |
LT1618
APPLICATIO N S I N FOR M ATIO N
R 1 = R 2 ? OUT – 1 ?
Setting Output Voltage
To set the output voltage, select the values of R1 and R2
(see Figure 1) according to the following equation.
? V ?
? 1 . 263 ?
For current source applications, use the FB pin for over-
voltage protection. Pick R1 and R2 so that the output
voltage will not go too high if the load is disconnected or
if the load current drops below the preset value. Typically
choose R1 and R2 so that the overvoltage value will be
about 20% to 30% higher than the normal output voltage
(when in constant-current mode). This prevents the volt-
age loop from interfering with the current loop in current
source applications. For battery charger applications, pick
the values of R1 and R2 to give the desired end of charge
voltage.
Selecting R SENSE /Current Sense Adjustment
Use the following formula to choose the correct current
sense resistor value (for constant current operation).
the output of the error amplifier (the V C pin) will be pulled
down and the LT1618 will stop switching.
A pulse width modulated (PWM) signal can also be used
to adjust the current sense voltage; simply add an RC
filterto convert the PWM signal into a DC voltage for the
I ADJ pin. If the I ADJ pin is not used, it should be tied to
ground. Do not leave the pin floating.
For applications needing only a simple one-step current
sense adjustment, the circuit in Figure 2 works well. If a
large value resistor ( ≥ 2M ? ) is placed between the I ADJ pin
and ground, the current sense voltage will reduce to about
25mV, providing a 50% reduction in current. Do not leave
the I ADJ pin open. This method gives a well-regulated
current value in both states, and is controlled by a logic
signal without the need for a variable PWM or DC control
signal. When the NMOS transistor is on, the current sense
voltage will be 50mV, when it is off, the current sense
voltage will be reduced to 25mV.
LT1618
I ADJ
R SENSE = 50mV/I MAX
For designs needing an adjustable current level, the I ADJ
pin is provided. With the I ADJ pin tied to ground, the
nominal current sense voltage is 50mV (appearing be-
tween the ISP and ISN pins). Applying a positive DC
FULL
CURRENT
2M
Figure 2
1618 F02
voltage to the I ADJ pin will decrease the current sense
voltage according to the following formula:
Considerations When Sensing Input Current
In addition to regulating the DC output current for current-
V ISENSE =
1.263V – (0 .8)V IADJ
25
source applications, the constant-current loop of the
LT1618 can also be used to provide an accurate input
current limit. Boost converters cannot provide output
For example, if 1V is applied to the I ADJ pin, the current
sense voltage will be reduced to about 18mV. This
adjustability allows the regulated current to be reduced
without changing the current sense resistor (e.g. to adjust
brightness in an LED driver or to reduce the charge current
in a battery charger). If the I ADJ pin is taken above 1.6V,
short-circuit protection, but the surge turn-on current can
be drastically reduced using the LT1618’s current sense
at the input. SEPICs, however, have an output that is DC-
isolated from the input, so an input current limit not only
helps soft-start the output but also provides excellent
short-circuit protection.
sn1618 1618fas
7
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