参数资料
| 型号： | MIC2169BYMME |
| 厂商： | Micrel Inc |
| 文件页数： | 9/25页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM VM 10-MSOP |
| 特色产品： | MIC2169B Buck Control IC |
| 标准包装： | 100 |
| PWM 型： | 电压模式 |
| 输出数： | 1 |
| 频率 - 最大： | 550kHz |
| 占空比： | 92% |
| 电源电压： | 3 V ~ 14.5 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： | 10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 |
| 包装： | 管件 |
| 产品目录页面： | 1092 (CN2011-ZH PDF) |
| 其它名称： | 576-3545-5 |
Micrel, Inc.
V IN
MOSFET Gate Drive
MIC2169B
C2
C IN
0.1μF
VSW
RCS
CS
HSD
LSD
Q1
MOSFET N
Q2
MOSFET N
L1 Inductor
1000pF
V OUT
C1
C OUT
The MIC2169B high-side drive circuit is designed to
switch an N-Channel MOSFET. The Functional Block
Diagram shows a bootstrap circuit, consisting of D1 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 VSW pin is approximately 0V.
When the high-side MOSFET driver is turned on, energy
R CS =
I L = I LOAD +
( V IN ? V OUT )
Inductor Ripple Current = V OUT ×
200 A
Figure 1. The MIC2169B Current Limiting Circuit
The current limiting resistor R CS is calculated by the
following equation:
R DS( ON)Q1 × I L
200 μA
where:
Inductor Ripple Current
2
V IN × F S × L
F S = 500kHz
200μA is the internal sink current to program the
MIC2169B 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) . To make the
MIC2169B insensitive to board layout and noise
generated by the switch node, a 1.4 ? resistor and a
1000pF capacitor is recommended between the switch
node and GND.
Internal V DD Supply
The MIC2169B 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
approximately 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 3.0V
to 5V.
from C BST is used to turn the MOSFET on. As the
MOSFET turns on, the voltage on the VSW pin
increases to approximately V IN . Diode D1 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 D1. 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 D1. An approximate
50ns delay between the high-side and low-side driver
transitions is used to prevent current from
simultaneously flowing unimpeded through both
MOSFETs (shoot-through).
Adaptive gate drive is implemented on the high-side (off)
to low-side (on) driver transition to reduce losses in the
flywheel diode and to prevent shoot-through. This is
operated by detecting the VSW pin; once this pin is
detected to reach 1.5V, the high-side MOSFET can be
assumed to be off and the low side driver is enabled.
Total Power Dissipation and Thermal Considerations
Total power dissipation in the MIC2169B equals the
power dissipation caused by driving the external
MOSFETs plus the quiescent supply current:
Pdiss TOTAL = Pdiss SUPPLY + Pdiss DRIVE
where:
Pdiss SUPPLY = V DD × I DD
I DD is shown in the “PWM Mode Supply Current” graph in
the Typical Characteristics section of the specification.
Pdiss DRIVE calculations are shown in the Applications
section of the specification.
The die temperature may be calculated once the total
power dissipation is known:
T J = T A + Pdiss TOTAL × θ JA
where:
T A is the maximum ambient temperature (°C)
T J is the junction temperature (°C)
Pdiss TOTAL is the power dissipation of the
MIC2169B (W)
θ JC is the thermal resistance from junction-to-
ambient air (°C/W)
April 2010
9
M9999-041210-B
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