参数资料
| 型号： | MIC9131BM TR |
| 厂商： | Micrel Inc |
| 文件页数： | 15/19页 |
| 文件大小： | 0K |
| 描述： | IC CTRLR DC-DC PWM HV HS 16-SOIC |
| 标准包装： | 2,500 |
| 应用： | 控制器，电信 |
| 输入电压： | 9 V ~ 18 V |
| 输出数： | 1 |
| 输出电压： | 4.7 V ~ 5 V |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-SOIC（0.154"，3.90mm 宽） |
| 供应商设备封装： | 16-SOIC |
| 包装： | 带卷 (TR) |
| 其它名称： | MIC9131BMTR MIC9131BMTR-ND |
MIC9131
series resistance is 10K, for a 500kHz switcher, the maximum
series resistance is 2K.
Sensing Current with a Resistor
The fast transition times of the current signal prohibit the use
of inductive resistors. Standard wire wound power resistors
will not work. Carbon composition or metal ?lm resistors or
low inductance power resistors may be used. The overcurrent
range of the power supply and component tolerances must be
considered when selecting the current sense resistor value.
The power supply speci?cation may call for an overcurrent
limit, which must be accounted for when selecting the cur-
rent sense resistor value. The relationship between the peak
primary current and the current sense resistor is:
Micrel, Inc.
Sensing Current with a Current Sense Transformer
At higher power levels, the power dissipation in a current sense
resistor is excessive. A current sense transformer can be
used to sense the current while minimizing power dissipation.
See Figure 11. The schematic shows the circuitry necessary
when using a current sense transformer. The resistor, R1,
provides a path to reset the current sense transformer. The
resistor, R2, converts the scaled down current to a voltage,
which is sent to the ISNS pin.
V IN
V ISNS = I P × R ISENSE + I ISNS × R f
where: Ip is the current in the sense resistor
R ISENSE is the current sense resistance
I ISNS is the current sourced from the ISNS pin
(40μA)
R f is the series resistor between the ISNS pin and
the current sense resistor.
I SNS
(pin 14)
MIC9131
OUT
(pin 16)
Rf
R2
R1
Current Sense
Transformer
I PRI
R SENSE = =
V SENSE 0.5
I SENSE
1
V ISNS = × R 2 + I ISNS × R f
V ISNS ? ( I P × R ISENSE ) 0 . 82 ? ( 1 × 0 . 5 )
I ISNS
R f = = 10 . 25 k ?
BW =
= 630 kHz
R 2 = SENSE
=
= 16 . 4 ?
? I
? 3 . 25 ?
?
P DISS = ? PRMS ? × R 2 = ? ? × 16 . 4 = 17 . 4 mW
The current sense resistor must not be too small or the cur-
rent sense signal will be susceptible to noise. If noise is a
problem, the current signal level should be increased.
An example is illustrated below.
The maximum peak current, I PMAX = 1A at 120% overcurrent
and minimum input voltage
The maximum rms current, I RMS =0.65A
The desired current sense signal amplitude is 500mV at 1A
output current.
The current sense resistor value and power dissipation is:
= 0.5 ?
P DISS = I RMS 2 × R SENSE = 0 . 65 2 × 0 . 5 = 0 . 21 W
A 0.5 ohm, non inductive resistor with at least a 1/2W rating
should be selected.
The series resistor is calculated to allow the 500mV-peak
signal to reach 0.82V.
40 μ A
The next lower value of 10kΩ is selected.
The bandwidth of the 10K resistor and the 25pF input capaci-
tance is calculated. The resistor value must be lowered if the
bandwidth is too low for the switching frequency.
1
2 × π × 10 k × 25 pF
The maximum switching frequency of this power supply
should be approximately six times less than the BW to pre-
vent current waveform distortion and excessive delays in
the current loop. This limits the switching frequency to the
range of 100kHz.
Figure 11
The voltage at the ISNS pin is calculated by:
I P
N
where: I P is the current in the primary of the current sense
transformer
R2 is the current sense resistance at the
secondary of the current sense transformer
N is the turns ratio of the current sense
transformer (N=Nsec/Npri)
I ISNS is the current sourced from the ISNS pin
(40μA)
R f is the series resistor between the ISNS pin and
the current sense resistor.
Current Transformer Example:
The maximum peak current, I PMAX = 5A at 120% overcurrent
and minimum input voltage
The maximum rms current, I RMS = 3.25A
The full 0.82V peak signal a the ISNS input can be used since
very little power is dissipation in the secondary side sense
resistor. The maximum peak to peak voltage at the sense
pin (pin 14) is 0.82V at the 5A maximum output current.
The current sense resistor value and power dissipation is:
V × N 0 . 82 × 100
I P 5
2 2
? N ? ? 100 ?
A 16.2 ohm, 1%, non inductive resistor with at least a 50mW
rating should be selected. A good choice would be an 0805
size metal ?lm or a 1/8 watt leaded metal ?lm resistor. A
series resistor between the current sense transformer and
the Isns input is not necessary unless it is used for low pass
?ltering.
August 2006
15
M9999-080206
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| MIC9131YM TR | 功能描述:电流型 PWM 控制器 SO-16 High Vin Telecom DC/DC PWM Control IC (Lead Free) RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| MIC9131YQS | 功能描述:电流型 PWM 控制器 SO-16 High Vin Telecom DC/DC PWM Control IC (Lead Free) RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
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