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| 型号： | MIC38C45AYMM TR |
| 厂商： | Micrel Inc |
| 文件页数： | 7/9页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST FLYBK ISO 8MSOP |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 500kHz |
| 占空比： | 50% |
| 电源电压： | 7.6 V ~ 20 V |
| 降压： | 是 |
| 升压： | 是 |
| 回扫： | 是 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 8-TSSOP，8-MSOP（0.118"，3.00mm 宽） |
| 包装： | 带卷 (TR) |
| 其它名称： | MIC38C45AYMMTR MIC38C45AYMMTR-ND |
MIC38C42A/43A/44A/45A
Application Information
Familiarity with 384x converter designs is assumed.
MIC38C4x Advantages
Start-up Current
Start-up current has been reduced to an ultra-low 50 μ A
(typical) permitting higher-valued, lower-wattage, start-up
resistors (powers controller during power supply start-up).
The reduced resistor wattage reduces cost and printed circuit
space.
Operating Current
Operating current has been reduced to 4mA compared to
11mA for a typical bipolar controller. The controller runs
cooler and the V DD hold-up capacitance required during
start-up may be reduced.
Output Driver
Complementary internal P- and N-channel MOSFETs pro-
duce rail-to-rail output voltages for better performance driving
external power MOSFETs. The driver transistor’s low on-
resistance and high peak current capability can drive gate
capacitances of greater than 1000pF. The value of output
capacitance which can be driven is determined only by the
rise/fall time requirements. Within the restrictions of output
capacity and controller power dissipation, maximum switch-
ing frequency can approach 500kHz.
Design Precautions
When operating near 20V, circuit transients can easily ex-
ceed the 20V absolute maximum rating, permanently damag-
ing the controller’s CMOS construction. To reduce tran-
sients, use a 0.1 μ F low-ESR capacitor to next to the controller’s
supply V DD (or V D for ‘-1’ versions) and ground connections.
Film type capacitors, such as Wima MKS2, are recom-
Micrel, Inc.
mended.
When designing high-frequency converters, avoid capacitive
and inductive coupling of the switching waveform into high-
impedance circuitry such as the error amplifier, oscillator, and
current sense amplifier. Avoid long printed-circuit traces and
component leads. Locate oscillator and compensation cir-
cuitry near the IC. Use high frequency decoupling capacitors
on V REF , and if necessary, on V DD . Return high d i/ d t currents
directly to their source and use large area ground planes.
Buck Converter
Refer to figure 1. When at least 26V is applied to the input,
C5 is charged through R2 until the voltage V DD is greater than
14.5V (the undervoltage lockout value of the MIC38C42).
Output switching begins when Q1 is turned on by the gate
drive transformer T1, charging the output filter capacitor C3
through L1. D5 supplies a regulated +12V to V DD once the
circuit is running.
Current sense transformer CT1 provides current feedback to
ISNS for current-mode operation and cycle-by-cycle current
limiting. This is more efficient than a high-power sense
resistor and provides the required ground-referenced level
shift.
When Q1 turns off, current flow continues from ground
through D1 and L1 until Q1 is turned on again.
The 100V Schottky diode D1 reduces the forward voltage
drop in the main current path, resulting in higher efficiency
than could be accomplished using an ultra-fast-recovery
diode. R1 and C2 suppress parasitic oscillations from D1.
Using a high-value inductance for L1 and a low-ESR capaci-
tor for C3 permits small capacitance with minimum output
ripple. This inductance value also improves circuit efficiency
by reducing the flux swing in L1.
V IN
26V to 40V
CT1
Q1
IRF820
V OUT
12V, 2A
100k
D2
M17Z105
1/4W
R2
68k
6.8k
0.1 μ F* MKS2
MIC38C42A
C5
4.7 μ F
D4
1N765B
4.7 ?
0.1 μ F
R1
10
1/2W
C2
1000pF
L1 48 μ H
31DQ10
D1
C3
3.3 μ F
C4
0.1 μ F
D3
MBR030
0.22 μ F
1
2
COMP VREF
FB VDD
8
7
D5
3
ISNS
OUT
6
T1
1N4001
6.19k
1%
R4
18
4
RT/CT GND
5
C8
0.1 μ F
1.62k
1%
C7
200pF
R5
16k
0.1 μ F
*Locate near MIC38C42 supply pins
Figure 1. 500kHz, 25W, Buck Converter
April 2005
7
M9999-042205
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| MIC38C45BM | 功能描述:IC REG CTRLR BST FLYBK ISO 8SOIC RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,000 系列:- PWM 型:电压模式 输出数:1 频率 - 最大:1.5MHz 占空比:66.7% 电源电压:4.75 V ~ 5.25 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:40-VFQFN 裸露焊盘 包装:带卷 (TR) |
| MIC38C45BM TR | 功能描述:IC REG CTRLR BST FLYBK ISO 8SOIC RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,000 系列:- PWM 型:电压模式 输出数:1 频率 - 最大:1.5MHz 占空比:66.7% 电源电压:4.75 V ~ 5.25 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:40-VFQFN 裸露焊盘 包装:带卷 (TR) |
| MIC38C45BMM | 功能描述:IC REG CTRLR BST FLYBK ISO 8MSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,000 系列:- PWM 型:电压模式 输出数:1 频率 - 最大:1.5MHz 占空比:66.7% 电源电压:4.75 V ~ 5.25 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:40-VFQFN 裸露焊盘 包装:带卷 (TR) |
| MIC38C45BMM TR | 功能描述:IC REG CTRLR BST FLYBK ISO 8MSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,000 系列:- PWM 型:电压模式 输出数:1 频率 - 最大:1.5MHz 占空比:66.7% 电源电压:4.75 V ~ 5.25 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:40-VFQFN 裸露焊盘 包装:带卷 (TR) |
| MIC38C45BN | 功能描述:IC REG CTRLR BST FLYBK ISO 8-DIP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,000 系列:- PWM 型:电压模式 输出数:1 频率 - 最大:1.5MHz 占空比:66.7% 电源电压:4.75 V ~ 5.25 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:40-VFQFN 裸露焊盘 包装:带卷 (TR) |
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