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參數(shù)資料
| 型號(hào)： | MIC2185 |
| 廠商： | Micrel Semiconductor,Inc. |
| 英文描述： | Low Voltage Synchronous Boost PWM Control IC |
| 中文描述： | 低電壓同步升壓PWM控制IC |
| 文件頁數(shù)： | 10/15頁 |
| 文件大?。?/td> | 141K |
| 代理商： | MIC2185 |
MIC2185
Micrel
MIC2185
10
May 2002
PWM Operation
PWM Mode Waveform
TIME (1
μ
s/div)
Switch Node Voltage
(Low Side FET Drain)
5V/div
V
IN
= 3.3V
High Side FET
Gate Drive
5V/div
Low Side FET
Gate Drive
5V/div
Inductor Current
1A offset; 0.5A/div
V
OUT
Ripple Voltage
200mV/div
V
OUT
= 5V
I
OUT
= 0.75A
Figure 5 - PWM mode waveforms
Figure 5 shows typical waveforms for PWM mode of opera-
tion. 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 flowing 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 com-
pensation 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 simplifies compensation. A simplified
current mode control diagram is shown in figure 6.
I_inductor
T
ON
T
PER
V
COMP
Gate Drive at OUTN
I_inductor
I_inductor
Gate Driver
I_inductor
Voltage
Divider
V
REF
V
IN
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 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 opera-
tion at duty cycles greater than 50%.
A transconductance amplifier is used as an error amplifier,
which compares an attenuated output voltage with a refer-
ence 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 error signal is brought out to
the COMP pin (pin 4) allowing the use of external compo-
nents 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, 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 flow 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, synchro-
nous operation of the MIC2185 forces the converter to always
operate in the continuous mode because current can flow
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.
The peak inductor current is:
I
I
1
2
V
I
I
V
V
I
V
V
fs L
2
V
IND(pk)
IND(ave)
IND(pp)
(
×
IND(pk)
O
O
η
IN
L
O
IN
O
=
+
×
=
×
×
+
×
×
(
)
)
×
η
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
f
S
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 resis-
tance and low side MOSFET on-resistance must be ac-
counted for at the lower input voltages that the MIC2185 can
operate at.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MIC2185_05 | 制造商:MICREL 制造商全稱:Micrel Semiconductor 功能描述:Low Voltage Synchronous Boost PWM Control IC |
| MIC2185BM | 功能描述:IC REG CTRLR BST PWM CM 16-SOIC RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:4,000 系列:- PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1.5MHz 占空比:66.7% 電源電壓:4.75 V ~ 5.25 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 85°C 封裝/外殼:40-VFQFN 裸露焊盤 包裝:帶卷 (TR) |
| MIC2185BM TR | 功能描述:IC REG CTRLR BST PWM CM 16-SOIC RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:4,000 系列:- PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1.5MHz 占空比:66.7% 電源電壓:4.75 V ~ 5.25 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 85°C 封裝/外殼:40-VFQFN 裸露焊盤 包裝:帶卷 (TR) |
| MIC2185BQS | 功能描述:IC REG CTRLR BST PWM CM 16-QSOP RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:4,000 系列:- PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1.5MHz 占空比:66.7% 電源電壓:4.75 V ~ 5.25 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 85°C 封裝/外殼:40-VFQFN 裸露焊盤 包裝:帶卷 (TR) |
| MIC2185BQS TR | 功能描述:IC REG CTRLR BST PWM CM 16-QSOP RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:4,000 系列:- PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1.5MHz 占空比:66.7% 電源電壓:4.75 V ~ 5.25 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 85°C 封裝/外殼:40-VFQFN 裸露焊盤 包裝:帶卷 (TR) |
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