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| 型号： | MIC9131YM TR |
| 厂商： | Micrel Inc |
| 文件页数： | 14/19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： | MIC9131YMTR MIC9131YMTR-ND |
T1
R1
D2
D1
Q G
I PK = 2 ×
I PK =
2 × 60 nC
= 2 . 4 A
MIC9131
C1
Gate Drive
Output
R2
GND
1:N
Figure 10
The gate impedance of a MOSFET is capacitive and the
power required to drive the gate is proportional to the charge
required to turn on the MOSFET, the peak gate voltage and
the switching frequency. Assuming the total gate charge for
turn on and turn off is equal, the power used to switch the
MOSFET on and off is:
P DRIVE = Q G × V GS × f S
where: Q G is the total gate charge at V GS
V GS is the gate to source voltage of the MOSFET
usually equal to V CC
f S is the output switching frequency
The power required to drive the MOSFET is dissipated in the
drive circuitry of the MIC9131. This power must not cause
the die temperature to exceed the maximum rated junction
temperature of 125°C.
MOSFET Driver IC’s are used when the drive requirement for
the MOSFETs is greater than the capability of the MIC9131
gate drive output. While the peak current of the MIC9131
gate drive is typically 1.2A at V IN =12V, a gate driver ICs
will sink or source between 1.2A and 12A of peak current.
The higher peak current allows faster rise and fall times for
larger MOSFETs.
The drive requirements for selecting a MOSFET driver are
determined using the following equation:
t
where: Q G is the total gate charge required to turn on
the MOSFET at a speci?ed I D , V G and V DS . This
information is usually given in the MOSFET
speci?cation sheet.
t is the gate voltage transition time (risetime or fall
time)
I PK is the peak current requirement of the
MOSFET driver IC.
For example, if a MOSFET is chosen with a Q G of 60nC and
it is desired to have a 50nS gate to source risetime/falltime,
the peak current requirement of the MOSFET driver is:
50 ns
A driver such as the MIC4424 will meet this requirement.
For more information on choosing a MOSFET driver, see
the Micrel application note AN-24, “Designing with Low Side
MOSFET Drivers.”
Micrel, Inc.
Current Sense Circuit
The current sense input of the MIC9131 has three unique
features, which are advantageous in a high speed, high ef-
?ciency power supply.
1. The overcurrent threshold is nominally 0.82V instead
of the typical 1.0V found in most switching control
ICs.
2. The current sense pin sources a nominal 40μA of
cur rent out of the pin. This is used to raise the current
limit threshold of the pin, which allows a smaller
current sense resistor to be used. This improves the
ef?ciency of the power supply, especially in lower
current applications.
3. The delay from the current sense input to the output
is typically 50ns.
The current limit threshold of the ISNS pin was set at 0.82V,
allowing the use of a smaller current sense resistor. A stable,
bandgap derived 40μA current is sourced from the ISNS pin.
A voltage drop across a series resistor placed between the
pin and the current sense resistor level increases the current
sense signal at the ISNS pin. This allows the use of a smaller
current sense resistor if the full 0.82V peak to peak current
signal is not required. Decreasing the value of the current
sense resistor decreases the power dissipation in the resistor,
which improves the ef?ciency of the power supply.
The delay between the input of the overcurrent comparator
and the output gate drive is nominally 50ns. This very fast
response time allows the MIC9131 to operate at higher fre-
quencies and still have adequate overcurrent protection.
The operation of the current sense input is as follows. The
sensed current in the power supply is converted to a volt-
age by a resistor or current sense transformer. Referring to
Figure 1, this voltage is compared to the output of the error
ampli?er, which sets the duty cycle of the gate drive output.
The current signal is also connected to an Imax comparator.
Comparing the current sense signal to the reference voltage
sets a maximum current limit. If the maximum amplitude of the
current sense signal exceeds the reference, the comparator
terminates the gate drive output pulse. It aslo discharges the
soft start capacitor when the CPWR pin is high.
Leading Edge Current Spike
The current signal in a power circuit will often have a leading
edge spike caused by leakage inductance, parasitic induc-
tance and capacitance, diode reverse recovery effects and
snubbers. These spikes can cause premature termination of
the switching cycle if they are not eliminated.
A resistor may be added in series between the current sense
resistor and the Isns input. The input and board trace ca-
pacitance of the ISNS pin (pin 14) is approximately 25pF. A
1k resistor is a good choice, since it attenuates most of the
ripple without distorting the current sense waveform. It has
a minimal effect on level, offsetting the current sense signal
by only 40mV.
A typical rule of thumb is the bandwidth of the RC ?lter
should be at least 6 times the switching frequency. This
avoids distorting the current sense waveform and adding
excessive delays in the current loop that will interfering with
overcurrent protection. For a 100kHz switcher, the maximum
M9999-080206
14
August 2006
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| 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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| MIC913BM5 TR | 功能描述:IC OPAMP 350MHZ HS LP SOT23-5 RoHS:否 类别:集成电路 (IC) >> Linear - Amplifiers - Instrumentation 系列:- 标准包装:2,500 系列:- 放大器类型:通用 电路数:1 输出类型:满摆幅 转换速率:0.11 V/µs 增益带宽积:350kHz -3db带宽:- 电流 - 输入偏压:4nA 电压 - 输入偏移:20µV 电流 - 电源:260µA 电流 - 输出 / 通道:20mA 电压 - 电源，单路/双路(±):2.7 V ~ 36 V，±1.35 V ~ 18 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 供应商设备封装:8-SO 包装:带卷 (TR) |
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