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参数资料
| 型号： | MIC2182YM TR |
| 厂商： | Micrel Inc |
| 文件页数： | 17/28页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 16-SOIC |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 330kHz |
| 占空比： | 86% |
| 电源电压： | 4.5 V ~ 32 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： | 16-SOIC（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
| 其它名称： | MIC2182YMTR MIC2182YMTR-ND |
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MIC2182
Micrel
charge can be a significant source of power dissipation in the
MIC2182. At low output load this power dissipation is notice-
able as a reduction in efficiency. The average current re-
t T =
C ISS × V GS + C OSS × V IN
I G
quired to drive the high-side MOSFET is:
I G[high-side](avg) = Q G × f S
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
with 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 losses for the low-side MOSFET is
usually negligable. Also, the gate drive current for the low-
side MOSFET is more accurately calculated using C ISS at
V DS = 0 instead of gate charge.
For the low-side MOSFET:
I G[low-side](avg) = C ISS × V GS × f S
Since the current from the gate drive comes from the input
voltage, the power dissipated in the MIC2182 due to gate
drive is:
P gate drive = V IN ( I G[high-side](avg) + I G[low-side](avg) )
A convenient figure of merit for switching MOSFETs is the on-
resistance times the total gate charge (R DS(on) × Q G ). Lower
numbers translate into higher efficiency. Low gate-charge
logic-level MOSFETs are a good choice for use with the
MIC2182. Power dissipation in the MIC2182 package limits
where:
C ISS and C OSS are measured at V DS = 0.
I G = gate drive current (1A for the MIC2182)
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 300kHz
The low-side MOSFET switching losses are negligible and
can be ignored for these calculations.
RMS Current and MOSFET Power Dissipation Calculation
Under normal operation, the high-side MOSFET ’ s RMS
current is greatest when V IN is low (maximum duty cycle). The
low-side MOSFET ’ s RMS current is greatest when V IN is high
(minimum duty cycle). However, the maximum stress the
MOSFETs see occurs during short circuit conditions, where
the output current is equal to I overcurrent(max) . (See the Sense
Resistor section). The calculations below are for normal
operation. To calculate the stress under short circuit condi-
tions, substitute I overcurrent(max) for I OUT(max) . Use the formula
below to calculate D under short circuit conditions.
D short circuit = 0.063 ? 1.8 × 10 ? 3 × V IN
The RMS value of the high-side switch current is:
D × ? I OUT(max)2 + PP ?
the maximum gate drive current. Refer to Figure 10 for the
MIC2182 gate drive limits.
Parameters that are important to MOSFET switch selection
are:
I SW(highside) (rms) =
? I 2 ?
? 12 ?
( 1 ? D ) ? I OUT(max)2 +
? Voltage rating
? On-resistance
? Total gate charge
I SW(low side) (rms) =
?
?
I PP2 ?
12 ? ?
D =
The voltage rating of the MOSFETs 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:
P conduction = I SW (rms) 2 × R SW
P AC = P AC(off) + P AC(on)
where:
D = duty cycle of the converter
V OUT
η × V IN
η = efficiency of the converter.
Converter efficiency depends on component parameters,
which have not yet been selected. For design purposes, an
efficiency of 90% can be used for V IN less than 10V and 85%
can be used for V IN greater than 10V. The efficiency can be
more accurately calculated once the design is complete. If the
assumed efficiency is grossly inaccurate, a second iteration
through the design procedure can be made.
For the high-side switch, the maximum dc power dissipation
R SW = on-resistance of the MOSFET switch.
Making the assumption the turn-on and turnoff transition
times are equal, the transition time can be approximated by:
April 22, 2004
17
is:
P switch1(dc) = R DS(on)1 × I SW1 (rms) 2
M9999-042204
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| MIC2182YSM | 功能描述:DC/DC 开关控制器 High EfficiencySynchronous Buck Controller SSOP Pkg (Lead Free) 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 |
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