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参数资料
| 型号： | MIC2196YM TR |
| 厂商： | Micrel Inc |
| 文件页数： | 8/12页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST FLYBK PWM 8SOIC |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 440kHz |
| 占空比： | 85% |
| 电源电压： | 2.9 V ~ 14 V |
| 降压： | 无 |
| 升压： | 是 |
| 回扫： | 是 |
| 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： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
| 其它名称： | MIC2196YMTR MIC2196YMTR-ND |
2 × I O × ( V O ? η × V IN )
I IND(pk) =
Micrel, Inc.
A block diagram of the MIC2196 PWM current mode
control loop is shown in Figure 1. The inductor current is
sensed by measuring the voltage across a resistor,
R SENSE . The current sense amplifier buffers and amplifies
this signal. A ramp is added to this signal to provide
slope compensation, which is required in current mode
control to prevent unstable operation at duty cycles
greater than 50%.
A transconductance amplifier is used as an error
amplifier, which compares an attenuated output voltage
MIC2196
V IN is the minimum input voltage
L is the value of the boost inductor
fs is the switching frequency
V O is the output voltage
Maximum Peak Current in Discontinuous Mode:
The peak inductor current is:
L × fs
with a reference voltage. The output of the error amplifier
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
where:
I O is the maximum output current
V O is the output voltage
R SENSE =
error signal is brought out to the COMP pin (pin 1) to
provide access to the output of the error amplifier. This
allows the use of external components to stabilize the
voltage loop.
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 and ground (R SENSE in Figure 1).
Exceeding the current limit threshold will immediately
terminate the gate drive of the N-Channel MOSFET, Q1.
This forces the Q1 to operate at a reduced duty cycle,
which lowers 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 flow from the input,
through the inductor and output diode to ground. Only
the impedance of the source and components limits the
V IN is the minimum input voltage
L is the value of the boost inductor
fs is the switching frequency
η is the efficiency of the boost converter
The maximum value of current sense resistor is:
V SENSE
I IND(pk)
where:
V is the minimum current sense threshold of the
CS pin.
Maximum Peak Current in Continuous Mode:
The peak inductor current is equal to the average
inductor current plus one half of the peak to peak
inductor current.
The peak inductor current is:
I IND(pk) = I IND(ave) +
× I IND(pp)
V O × I O V L × ( V O ? V IN × η )
current.
The mode of operation (continuous or discontinuous),
the minimum input voltage, maximum output power and
the minimum value of the current limit threshold
determine the value of the current sense resistor.
Discontinuous mode is where all the energy in the
inductor is delivered to the output at each switching
cycle. Continuous mode of operation occurs when
current always flows in the inductor, during both the low-
where:
1
2
I IND(pk) = +
V IN × η 2 × V O × fs × L
I O is the maximum output current
V O is the output voltage
V IN × ( V O ? V IN ) × η
side MOSFET on and off times. The equations below will
help to determine the current sense resistor value for
each operating mode.
The critical value of output current in a boost converter is
calculated below. The operating mode is discontinuous if
the output current is below this value and is continuous if
above this value.
2
I CRIT = 2
2 × fs × L × V O
where:
η is the efficiency of the boost converter
V IN is the minimum input voltage
L is the value of the boost inductor
fs is the switching frequency
η is the efficiency of the boost converter
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
MIC2196 operates at:
September 2008
8
M9999-092908
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