参数资料
| 型号： | LT1619ES8#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 8/20页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR PWM CM 8-SOIC |
| 标准包装： | 100 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 500kHz |
| 占空比： | 92% |
| 电源电压： | 1.9 V ~ 18 V |
| 降压： | 无 |
| 升压： | 是 |
| 回扫： | 是 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 是 |
| 隔离： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 管件 |
| 产品目录页面： | 1328 (CN2011-ZH PDF) |
LT1619
APPLICATIO S I FOR ATIO
Transition Loss = I D
Power MOSFET
MOSFET power dissipation can be separated into fre-
quency independent and frequency dependent compo-
nents. The R DS(ON) loss in the switch is the product of the
mean square switch current and switch R DS(ON) and it
does not vary with the operating frequency.
The frequency-dependent switching losses consist of 1)
switch transition loss due to finite rise and fall times of the
drain source voltage and the drain current 2) gate switch-
ing loss, i.e., a packet of charge Q g (the total gate charge)
which is moved from the gate drive power supply to
ground in every switch cycle, and 3) the drain switching
loss, charge stored on the parasitic drain capacitance,
C OSS is dumped to ground as the switch is turned on. The
transistor loss can be expressed as:
P LOSS = I DRMS2 R DS(ON) + transition loss + Q g V G f S
+ 1/2C OSS V DS(OFF)2 f S
where the transition loss can be estimated with:
2
C RSS V DS(OFF ) f S
I G ( AVG )
Q g = The total gate charge
V G = Gate drive voltage ≈ V DRV
I G(AVG) = The average MOSFET buffer output current
f S = Operating frequency
C RSS = The average C GD between V DS = 0V
and V DS = V DS(OFF)
the output capacitor and the peak-to-peak capacitor
current. Depending on topology, current feeding the out-
put capacitor can be continuous or discontinuous. The input
current can also be continuous or discontinuous even if the
inductor current itself is continuous. In boost topology, the
inductor is in series with the input source so the input
current is continuous and the output current is discontinu-
ous. In buck-boost or flyback converters, the inductor is
not in series with the input source nor the output, so nei-
ther the input current nor output current is continuous.
Whenever a terminal current is discontinuous, the capaci-
tor at that terminal should be chosen to handle the ripple
current. Capacitor reliability will be adversely affected if
the ripple current exceeds the maximum allowable rat-
ings. This maximum rating is specified as the RMS ripple
current. Several capacitors may be mounted in parallel to
meet the size and ripple current requirements.
Besides the ripple voltage requirements, the output ca-
pacitor also needs to be sized for acceptable output
voltage variation under load transients.
Current Sensing Resistor R SENSE
The LT1619 drives a low side N-channel MOSFET switch.
The switch current is sensed with an external resistor
R SENSE connected between the source of the MOSFET and
ground. The internal blanking circuit blocks the voltage
spike developed across R SENSE for 280ns at switch turn-
on. The switch is turned off when the instantaneous
voltage across R SENSE exceeds the current limit threshold,
V SENSE . Allowing variations in V SENSE yields:
At low V DS(OFF) ( ≤ 12V) and operating frequencies below
500kHz, the ohmic losses often dominate. For high voltage
converters, the transition loss and C OSS charge dumping
R SENSE =
V SENSE(MIN)
I L ( MAX )
loss can dramatically impact the converter efficiency.
MOSFETs with lower parasitic capacitances but higher
R DS(ON) may actually provide better efficiency in these
situations.
Capacitors
In a switch mode DC/DC converter, output ripple voltage
is the product of the equivalent series resistance (ESR) of
The current limit threshold is constant and does not vary
with duty ratio.
Due to low signal level of the sense voltage, low inductance
sense resistors are required to reduce switching noise.
Low TC resistors maintain constant current limit over
temperature. Dale WSL and IRC series sense resistors
meet these criteria.
1619fa
8
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