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33710 参数 Datasheet PDF下载

33710图片预览
型号: 33710
PDF下载: 下载PDF文件 查看货源
内容描述: 双输出DC-DC与线性稳压器IC [Dual Output DC-DC & Linear Regulator IC]
分类和应用: 线性稳压器IC
文件页数/大小: 17 页 / 508 K
品牌: FREESCALE [ Freescale ]
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TYPICAL APPLICATIONS  
TYPICAL APPLICATIONS  
C1  
330 µF  
B+  
13 V - 32 V  
R1  
1 K  
C1  
0.1 mF  
SW1  
C5  
32  
1
0.1 µF  
CT  
CP1  
CP2  
VB  
RST  
2
3
4
31  
30  
29  
28  
27  
26  
25  
24  
23  
MODE0  
MODE1  
MODE2  
CHARGE  
PUMP  
C6  
10 µF  
L1  
100 µH  
B+  
BUCK  
REG  
SUPERVISORY  
& SHUTDOWN  
VSW  
VFB  
LINB  
C8  
330 µF  
LDO  
RSERIES  
1.8  
D1  
VCORE  
MBRS130LT3  
13  
GND  
MC34710  
1
2
V I/O  
VCORE  
Figure 4. Typical Application Diagram  
The MC34710 provides both a buck converter and an LDO  
regulator in one IC. Figure 4 above shows a typical  
application schematic for the MC34710. L1 is the buck  
converter's inductor. The buck inductor is a key component  
and must not only present the required reactance, but do so  
at a dc resistance of less than 20 milliohms in order to  
preserve the converter's efficiency. Also important to the  
converter's efficiency is the utilization of a low Vf Schottky  
diode for D1.  
temperature is maintained below 105 degrees C. The heat-  
generating power dissipation of the LDO is primarily a  
function of the Volt x Amp product across the LINB+ and  
VCORE terminals. Therefore, if the LINB+ voltage is >> than  
the selected VCORE voltage + 0.8 V, it is recommended to use  
a power resistor in series with the LINB+ input to drop the  
voltage and dissipate the heat externally from the IC. For  
example, if the output of the buck regulator (V I/O on the  
schematic) is used as the input to LINB+, and the mode  
switches are set such that V I/O = 5 V and VCORE = 3.3 V,  
then a series resistance of 1.8 ohms at the LINB+ pin would  
provide an external voltage drop at 500 mA while still leaving  
the minimum required headroom of 0.8 V. Conversely, if the  
Note that a 0.1uF capacitor is connected between CT and  
the reset pins; this prevents any possibility of oscillations  
occurring on the reset line during transitions by allowing the  
CT terminal to discharge to ground potential via the RST pin,  
and then charge when RST returns to a logic high. The  
capacitor between the CP1 and CP2 pins is the charge  
pump's “bucket capacitor”, and sequentially charges and  
discharges to pump up the reservoir capacitor connected to  
the VB pin. Note that the reservoir capacitor's cathode is  
connected to B+ rather than ground. Also note that the  
charge pump is intended only to provide gate-drive potential  
for the buck regulator's internal power MOSFET, and  
therefore connecting external loads to the VB pin is not  
recommended.  
mode switches are set such that V I/O = 3.3 V and VCORE  
=
2.5 V, then no series resistance would be required, even at  
the maximum output current of 500 mA.  
Designing a power supply circuit with the MC34710, like all  
dc-dc converter ICs, requires special attention not only to  
component selection, but also to component placement (i.e.,  
printed circuit board layout). The MC34710 has a nominal  
switching frequency of 200 kHz, and therefore pcb traces  
between the buck converter discrete component terminals  
and the IC should be kept as short and wide as possible to  
keep the parasitic inductance low. Likewise, keeping these  
The IC's internal VCORE LDO regulator can provide up to  
500 mA of current as long as the operating junction  
34710  
Analog Integrated Circuit Device Data  
Freescale Semiconductor  
11