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參數(shù)資料
| 型號(hào)： | MIC2169 |
| 廠商： | Micrel Semiconductor,Inc. |
| 英文描述： | 500 KHZ PWM SYNCHRONOUS BUCK CONTROL IC |
| 中文描述： | 500千赫的PWM同步降壓控制IC |
| 文件頁數(shù)： | 7/14頁 |
| 文件大?。?/td> | 160K |
| 代理商： | MIC2169 |
November 2003
7
M9999-111803
MIC2169
Micrel
0.65V. After this counting cycle the COMP current source is
reduced to 8.5
μ
A and the COMP pin voltage rises from 0.65V
to 0.95V, the bottom edge of the saw-tooth oscillator. This is
the beginning of 0% duty cycle and it increases slowly
causing the output voltage to rise slowly. The MIC2169 has
two hysteretic comparators that are enabled when V
OUT
is
within
±
3% of steady state. When the output voltage reaches
97% of programmed output voltage then the g
m
error ampli-
fier is enabled along with the hysteretic comparator. This
point onwards, the voltage control loop (g
m
error amplifier) is
fully in control and will regulate the output voltage.
Soft-start time can be calculated approximately by adding the
following four time frames:
t1 = Cap_COMP
×
0.18V/8.5
μ
A
t2 = 12 bit counter, approx 2ms
t3 = Cap_COMP
×
0.3V/8.5
μ
A
t4
V
V
0.5
Cap_COMP
8.5 A
OUT
IN
=
×
×
Soft-Start Time(Cap_COMP=100nF) = t1 + t2 + t3 +
t4 = 2.1ms + 2ms + 3.5ms + 1.8ms = 10ms
Current Limit
The MIC2169 uses the R
DS(ON)
of the top power MOSFET to
measure output current. Since it uses the drain to source
resistance of the power MOSFET, it is not very accurate. This
scheme is adequate to protect the power supply and external
components during a fault condition by cutting back the time
the top MOSFET is on if the feedback voltage is greater than
0.67V. In case of a hard short when feedback voltage is less
than 0.67V, the MIC2169 discharges the COMP capacitor to
0.65V, resets the digital counter and automatically shuts off
the top gate drive, and the g
m
error amplifier and the
–
3%
hysteretic comparators are completely disabled and the soft-
start cycles restarts. This mode of operation is called the
“
hiccup mode
”
and its purpose is to protect the down stream
load in case of a hard short. The circuit in Figure 1 illustrates
the MIC2169 current limiting circuit.
L1 Inductor
V
IN
V
OUT
HSD
LSD
RCS
CS
200
μ
A
0
C2
C
IN
C1
C
OUT
Q1
MOSFET N
Q2
MOSFET N
Figure 1. The MIC2169 Current Limiting Circuit
The current limiting resistor R
CS
is calculated by the following
equation:
R
R
I
200 A
CS
DS(ON) Q1
L
=
×
Equation (1)
I
I
1
2 Inductor Ripple Current
L
LOAD
=
+
)
where:
Inductor Ripple Current =
V
V
F
–
V
V
L
OUT
IN
OUT
IN
SWITCHING
×
(
×
)
×
F
SWITCHING
= 500kHz
200
μ
A is the internal sink current to program the MIC2169
current limit.
The MOSFET R
DS(ON)
varies 30% to 40% with temperature;
therefore, it is recommended to add a 50% margin to the load
current (I
LOAD
) in the above equation to avoid false current
limiting due to increased MOSFET junction temperature rise.
It is also recommended to connect R
CS
resistor directly to the
drain of the top MOSFET Q1, and the R
SW
resistor to the
source of Q1 to accurately sense the MOSFETs R
DS(ON)
. A
0.1
μ
F capacitor in parallel with R
CS
should be connected to
filter some of the switching noise.
Internal V
DD
Supply
The MIC2169 controller internally generates V
DD
for self
biasing and to provide power to the gate drives. This V
DD
supply is generated through a low-dropout regulator and
generates 5V from V
IN
supply greater than 5V. For supply
voltage less than 5V, the V
DD
linear regulator is approxi-
mately 200mV in dropout. Therefore, it is recommended to
short the V
DD
supply to the input supply through a 10
resistor for input supplies between 2.9V to 5V.
MOSFET Gate Drive
The MIC2169 high-side drive circuit is designed to switch an
N-Channel MOSFET. The block diagram in Figure 2 shows
a bootstrap circuit, consisting of D2 and CBST, supplies
energy to the high-side drive circuit. Capacitor CBST is
charged while the low-side MOSFET is on and the voltage on
the VSW pin is approximately 0V. When the high-side
MOSFET driver is turned on, energy from CBST is used to
turn the MOSFET on. As the MOSFET turns on, the voltage
on the VSW pin increases to approximately V
IN
. Diode D2 is
reversed biased and CBST floats high while continuing to
keep the high-side MOSFET on. When the low-side switch is
turned back on, CBST 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. An approximate 20ns delay between
the high- and low-side driver transitions is used to prevent
current from simultaneously flowing unimpeded through both
MOSFETs.
MOSFET Selection
The MIC2169 controller works from input voltages of 3V to
13.2V and has an internal 5V regulator to provide power to
turn the external N-Channel power MOSFETs for high- and
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相關(guān)代理商/技術(shù)參數(shù) |
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|---|---|
| MIC2169_09 | 制造商:MICREL 制造商全稱:Micrel Semiconductor 功能描述:500kHz PWM Synchronous Buck Control IC |
| MIC2169A | 制造商:MICREL 制造商全稱:Micrel Semiconductor 功能描述:500kHz PWM Synchronous Buck Control IC |
| MIC2169A_09 | 制造商:MICREL 制造商全稱:Micrel Semiconductor 功能描述:500kHz PWM Synchronous Buck Control IC |
| MIC2169ABMM | 功能描述:IC REG CTRLR DIVIDER PWM 10-MSOP 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) |
| MIC2169ABMM TR | 功能描述:IC REG CTRLR DIVIDER PWM 10-MSOP 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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