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| 型号： | MIC2185BQS |
| 厂商： | Micrel Inc |
| 文件页数： | 10/15页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST PWM CM 16-QSOP |
| 标准包装： | 98 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 440kHz |
| 占空比： | 95% |
| 电源电压： | 2.9 V ~ 14 V |
| 降压： | 无 |
| 升压： | 是 |
| 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 ~ 125°C |
| 封装/外壳： | 16-SSOP（0.154"，3.90mm 宽） |
| 包装： | 管件 |
MIC2185
Micrel, Inc.
PWM Operation
Switch NodeVoltage
(Low Side FET Drain)
5V/div
High Side FET
Gate Drive
5V/div
Low Side FET
Gate Drive
5V/div
Inductor Current
1A offset; 0.5A/div
V IN = 3.3V
PWM ModeWaveform
V OUT = 5V I OUT = 0.75A
required in current mode control to prevent unstable operation
at duty cycles greater than 50%.
A transconductance ampli?er is used as an error ampli?er,
which compares an attenuated output voltage with a refer-
ence voltage. The output of the error ampli?er is compared
to the current sense waveform in the PWM block. When the
current signal rises above the error voltage, the comparator
turns off the low side drive. The error signal is brought out to
the COMP pin (pin 4) allowing the use of external components
to stabilize the voltage loop.
V OUT RippleVoltage
200mV/div
TIME (1μs/div)
Figure 5 - PWM mode waveforms
Figure 5 shows typical waveforms for PWM mode of operation.
The gate drive signal turns on the external low side MOSFET,
Q1, allowing the inductor current to ramp up. When the low
side MOSFET turns off and the high side MOSFET, Q2, turns
on, current ?owing in the inductor forces the MOSFET drain
voltage to rise until the is clamped at approximately the output
voltage. The MIC2185 uses current mode control to improve
output regulation and simplify compensation of the control
loop. Current mode control senses both the output voltage
(outer loop) and the inductor current (inner loop). It uses the
inductor current and output voltage to determine the duty
cycle (D) of the buck converter. Sampling the inductor current
effectively removes the inductor from the control loop, which
simpli?es compensation. A simpli?ed current mode control
diagram is shown in ?gure 6.
I_inductor
V IN
Current Sensing and Overcurrent Protection
The inductor current is sensed during the switch on time by
a current sense resistor located between the source of the
MOSFET, Q1 and ground (R SENSE in Figure 1). Exceeding
the current limit threshold will immediately terminate the
gate drive of the N-channel MOSFET. This forces the Q1 to
operate at a reduced duty cycle, which reduces the output
voltage. In a boost converter, the overcurrent limit will
not protect the power supply or load during a severe
overcurrent condition or short circuit condition. If the
output is short-circuited to ground, current will ?ow from the
input, through the inductor and output diode,D1, to ground.
Only the impedance of the source and components limits
the current.
The minimum input voltage, maximum output power and
the minimum value of the current limit threshold determine
the value of the current sense resistor. The two switch, syn-
chronous operation of the MIC2185 forces the converter to
always operate in the continuous mode because current can
?ow both ways through the high side P-channel MOSFET.
The equations below will help to determine the current sense
resistor value.
Maximum Peak Current
The peak inductor current is equal to the average inductor
current plus one half of the peak to peak inductor current.
I IND(pk) = I IND(ave) +
× I IND(pp)
V O × I O V L × ( V O ? ( V IN × η ) )
V IN × η
2 × V O × fs × L
Gate Driver
V COMP
I_inductor
I_inductor
I_inductor
Voltage
Divider
V REF
The peak inductor current is:
1
2
I IND(pk) = +
where:
I O is the maximum output current
V O is the output voltage
V IN is the minimum input voltage
L is the value of the boost inductor
T ON
Gate Drive at OUTN
f S is the switching frequency
η is the ef?ciency of the boost converter
T PER
Figure 6. PWM Control Loop
A block diagram of the MIC2185 PWM current mode control
loop is shown in Figure 1. The inductor current is sensed by
measuring the voltage across a resistor, Rsense. The current
sense ampli?er buffers and ampli?es this signal. A ramp is
added to this signal to provide slope compensation, which is
V L is the voltage across the inductor
V L may be approximated as V IN for higher input voltage.
However, the voltage drop across the inductor winding
resistance and low side MOSFET on-resistance must be
accounted for at the lower input voltages that the MIC2185
can operate at:
MIC2185
10
October 2005
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MIC2185BQS TR | 功能描述:IC REG CTRLR BST PWM CM 16-QSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,000 系列:- PWM 型:电压模式 输出数:1 频率 - 最大:1.5MHz 占空比:66.7% 电源电压:4.75 V ~ 5.25 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:40-VFQFN 裸露焊盘 包装:带卷 (TR) |
| MIC2185YM | 功能描述:DC/DC 开关控制器 SO-16 Low Vin Synchronous Buck PWM Control IC (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 |
| MIC2185YM TR | 功能描述:DC/DC 开关控制器 SO-16 Low Vin Synchronous Buck PWM Control IC (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 |
| MIC2185YQS | 功能描述:DC/DC 开关控制器 SO-16 Low Vin Synchronous Buck PWM Control IC (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 |
| MIC2185YQS TR | 功能描述:DC/DC 开关控制器 SO-16 Low Vin Synchronous Buck PWM Control IC (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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