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參數(shù)資料
| 型號： | MIC2199 |
| 廠商： | Micrel Semiconductor,Inc. |
| 英文描述： | 300kHz 4mm 】 4mm Synchronous Buck Converter |
| 中文描述： | 300kHz的4毫米】4mm的同步降壓轉(zhuǎn)換器 |
| 文件頁數(shù)： | 8/15頁 |
| 文件大?。?/td> | 222K |
| 代理商： | MIC2199 |
MIC2199
Micrel
MIC2199
8
November 2004
Current Limit
The MIC2199 output current is detected by the voltage drop
across the external current-sense resistor (R
CS
in Figure 2.).
The current limit threshold is 75mV
±
20mV. The current-
sense resistor must be sized using the minimum current limit
threshold. The external components must be designed to
withstand the maximum current limit. The current-sense
resistor value is calculated by the equation below:
R
55mV
I
CS
OUT(max)
=
The maximum output current is:
I
95mV
R
CS
OUT(max)
=
The current-sense pins CSH (pin 4) and V
OUT
(pin 5) are
noise sensitive due to the low signal level and high input
impedance. The PCB traces should be short and routed close
to each other. A small (1nF to 0.1
μ
F) capacitor across the
pins will attenuate high frequency switching noise.
When the peak inductor current exceeds the current limit
threshold, the current limit comparator, in Figure 2, turns off
the high-side MOSFET for the remainder of the cycle. The
output voltage drops as additional load current is pulled from
the converter. When the output voltage reaches approxi-
mately 0.4V, the circuit enters frequency-foldback mode and
the oscillator frequency will drop to 75kHz while maintaining
the peak inductor current equal to the nominal 75mV across
the external current-sense resistor. This limits the maximum
output power delivered to the load under a short circuit
condition.
Reference, Enable and UVLO Circuits
The output drivers are enabled when the following conditions
are satisfied:
The V
DD
voltage (pin 7) is greater than its under-
voltage threshold (typically 4.25V).
The voltage on the enable pin is greater than the
enable UVLO threshold (typically 2.5V).
The internal bias circuit generates a 0.8V bandgap reference
voltage for the voltage error amplifier and a 5V V
DD
voltage
for the gate drive circuit. The MIC2199 uses FB (pin 3) for
output voltage sensing.
The enable pin (pin 2) has two threshold levels, allowing the
MIC2199 to shut down in a low current mode, or turn off output
switching in UVLO mode. An enable pin voltage lower than
the shutdown threshold turns off all the internal circuitry and
reduces the input current to typically 0.1
μ
A.
If the enable pin voltage is between the shutdown and UVLO
thresholds, the internal bias, V
DD
, and reference voltages are
turned on. The output drivers are inhibited from switching and
remain in a low state. Raising the enable voltage above the
UVLO threshold of 2.5V enables the output drivers.
Either of two UVLO conditions will disable the MIC2199 from
switching.
When the V
DD
drops below 4.1V
When the enable pin drops below the 2.5V threshold
MOSFET Gate Drive
The MIC2199 high-side drive circuit is designed to switch an
N-Channel MOSFET. Referring to the block diagram in
Figure 2, a bootstrap circuit, consisting of D2 and C
BST
,
supplies energy to the high-side drive circuit. Capacitor C
BST
is charged while the low-side MOSFET is on and the voltage
on the V
SW
pin (pin 11) is approximately 0V. When the high-
side MOSFET driver is turned on, energy from C
BST
is used
to turn the MOSFET on. As the MOSFET turns on, the voltage
on the V
SW
pin increases to approximately V
IN
. Diode D2 is
reversed biased and C
BST
floats high while continuing to
keep the high-side MOSFET on. When the low-side switch is
turned back on, C
BST
is recharged through D2.
The drive voltage is derived from the internal 5V V
DD
bias
supply. The nominal low-side gate drive voltage is 5V and the
nominal high-side gate drive voltage is approximately 4.5V
due the voltage drop across D2. A fixed 80ns delay between
the high- and low-side driver transitions is used to prevent
current from simultaneously flowing unimpeded through both
MOSFETs.
Oscillator
The internal oscillator is free running and requires no external
components. The nominal oscillator frequency is 500kHz. If
the output voltage is below approximately 0.4V, the oscillator
operates in a frequency-foldback mode and the switching
frequency is reduced to 75kHz.
Figure 4. Startup Waveform
Above 0.4V, the switching frequency increases to 500kHz
causing the output voltage to rise a greater rate. The rise time
of the output is dependent on the output capacitance, output
voltage, and load current. The oscilloscope photo in Figure 4
show the output voltage at startup.
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| MIC2199_10 | 制造商:MICREL 制造商全稱:Micrel Semiconductor 功能描述:300kHz 4mm × 4mm Synchronous Buck Converter |
| MIC2199BML | 功能描述:IC REG CTRLR BUCK PWM CM 12-MLF RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝: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) |
| MIC2199BML TR | 功能描述:IC REG CTRLR BUCK PWM CM 12-MLF RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝: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) |
| MIC2199YML | 功能描述:DC/DC 開關(guān)控制器 300KHz 12 Lead Sync Buck Controller - Lead Free RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| MIC2199YML EV | 功能描述:電源管理IC開發(fā)工具 300KHz 12 Lead Sync Buck Controller - Evaluation Board RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
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