参数资料
| 型号： | MIC2169BMM TR |
| 厂商： | Micrel Inc |
| 文件页数： | 8/15页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM VM 10-MSOP |
| 标准包装： | 2,500 |
| PWM 型： | 电压模式 |
| 输出数： | 1 |
| 频率 - 最大： | 550kHz |
| 占空比： | 92% |
| 电源电压： | 3 V ~ 14.5 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 10-TFSOP，10-MSOP（0.118"，3.00mm 宽） |
| 包装： | 带卷 (TR) |
| 其它名称： | MIC2169BMMTR MIC2169BMMTR-ND |
P AC AC(off) AC(on)
D = duty cycle ? O ?
MIC2169
at V GS = 4.5V must be used.
It is important to note the on-resistance of a MOSFET increases
with rising temperature. A 75°C rise in junction temperature
will increase the channel resistance of the MOSFET by 50%
to 75% of the resistance speci ? ed at 25°C. This change in
resistance must be accounted for when calculating MOSFET
power dissipation and in calculating the value of current-sense
(CS) resistor. Total gate charge is the charge required to turn
the MOSFET on and off under speci ? ed operating conditions
(V DS and V GS ). The gate charge is supplied by the MIC2169
gate-drive circuit. At 500kHz switching frequency and above,
Micrel
where:
P CONDUCTION = I SW(rms) 2 × R SW
= P + P
R SW = on-resistance of the MOSFET switch
? V ?
? V IN ?
Making the assumption the turn-on and turn-off transition times
are equal; the transition times can be approximated by:
the gate charge can be a signi ? cant source of power dissipa-
tion in the MIC2169. At low output load, this power dissipation
is noticeable as a reduction in ef ? ciency. The average current
t T =
C ISS × V GS + C OSS × V IN
I G
I G[high-side](avg) G S
I G[low-side](avg) ISS GS S
required to drive the high-side MOSFET is:
= Q × f
where:
I G[high-side](avg) = average high-side MOSFET gate
current.
Q G = total gate charge for the high-side MOSFET taken from
manufacturer ’s data sheet for V GS = 5V.
The low-side MOSFET is turned on and off at V DS = 0 because
the freewheeling diode is conducting during this time. The
switching loss for the low-side MOSFET is usually negligible.
Also, the gate-drive current for the low-side MOSFET is
more accurately calculated using CISS at V DS = 0 instead
of gate charge.
For the low-side MOSFET:
= C × V × f
Since the current from the gate drive comes from the input
voltage, the power dissipated in the MIC2169, due to gate
drive, is:
where:
C ISS and C OSS are measured at V DS = 0
I G = gate-drive current (1A for the MIC2169)
The total high-side MOSFET switching loss is:
P AC = (V IN + V D ) × I PK × t T × f S
where:
t T = switching transition time (typically 20ns to 50ns)
V D = freewheeling diode drop, typically 0.5V
f S it the switching frequency, nominally 500kHz
The low-side MOSFET switching losses are negligible and
can be ignored for these calculations.
Inductor Selection
Values for inductance, peak, and RMS currents are required
to select the output inductor. The input and output voltages
and the inductance value determine the peak-to-peak induc-
tor ripple current. Generally, higher inductance values are
used with higher input voltages. Larger peak-to-peak ripple
currents will increase the power dissipation in the inductor
P GATEDRIVE = V IN ( I G[high-side](avg) + I G[low-side](avg)
)
and MOSFETs. Larger output ripple currents will also require
more output capacitance to smooth out the larger ripple cur-
A convenient ? gure of merit for switching MOSFETs is the on
resistance times the total gate charge R DS(ON) × Q G . Lower
numbers translate into higher ef ? ciency. Low gate-charge
logic-level MOSFETs are a good choice for use with the
MIC2169.
rent. Smaller peak-to-peak ripple currents require a larger
inductance value and therefore, a larger and more expensive
inductor. A good compromise between size, loss and cost is
to set the inductor ripple current to be equal to 20% of the
maximum output current. The inductance value is calculated
by the equation below.
Parameters that are important to MOSFET switch selection
are:
? Voltage rating
L =
V OUT × (V IN ( max ) ? V OUT )
V IN ( max ) × f S × 0.2 × I OUT ( max )
V OUT × (V IN ( max ) ? V OUT )
? On-resistance
? Total gate charge
The voltage ratings for the top and bottom MOSFET are
essentially equal to the input voltage. A safety factor of 20%
should be added to the V DS (max) of the MOSFETs to account
for voltage spikes due to circuit parasitics.
The power dissipated in the switching transistor is the sum
of the conduction losses during the on-time (P CONDUCTION )
and the switching losses that occur during the period of time
when the MOSFETs turn on and off (P AC ).
P SW = P CONDUCTION + P AC
where:
f S = switching frequency, 500kHz
0.2 = ratio of AC ripple current to DC output current
V IN (max) = maximum input voltage
The peak-to-peak inductor current (AC ripple current) is:
I PP =
V IN ( max ) × f S × L
The peak inductor current is equal to the average output current
plus one half of the peak-to-peak inductor ripple current.
M9999-032409
8
March 2009
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相关代理商/技术参数 |
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| MIC2169BYMM | 功能描述:DC/DC 开关控制器 500kHz PWM Synchronous Buck Controller RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| MIC2169BYMM TR | 功能描述:DC/DC 开关控制器 500kHz PWM Synchronous Buck Controller RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| MIC2169BYMME | 功能描述:直流/直流开关转换器 Synchronous Step Down Converter RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| MIC2169BYMME TR | 功能描述:直流/直流开关转换器 Synchronous Step Down Converter RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| MIC2169MM | 制造商:MICREL 制造商全称:Micrel Semiconductor 功能描述:500 KHZ PWM SYNCHRONOUS BUCK CONTROL IC |
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