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MAX1044ESA 参数 Datasheet PDF下载

MAX1044ESA图片预览
型号: MAX1044ESA
PDF下载: 下载PDF文件 查看货源
内容描述: 开关电容电压转换器 [Switched-Capacitor Voltage Converters]
分类和应用: 转换器稳压器开关式稳压器或控制器电源电路开关式控制器光电二极管
文件页数/大小: 12 页 / 118 K
品牌: MAXIM [ MAXIM INTEGRATED PRODUCTS ]
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S w it c h e d -Ca p a c it o r Vo lt a g e Co n ve rt e rs  
MAX14/ICL760  
CONNECTION  
FROM V+  
TO BOOST  
V+  
1
2
3
4
8
7
6
5
V
OUT  
= -(V+)  
V+  
1
2
3
4
8
7
6
5
C
BYPASS  
MAX1044  
ICL7660  
C1  
10µF  
C2  
10µF  
MAX1044  
10µF  
C
OSC  
*
V
OUT  
= -(V+)  
10µF  
*REQUIRED FOR V+ < 3.5V  
Figure 5. Basic Negative Voltage Converter  
Figure 6. Negative Voltage Converter with COSC and BOOST  
a nd a llow op e ra tion d own to 1.5V. For low-volta g e  
operation and compatibility with the industry-standard  
LTC1044 and ICL7660, the LV pin should be connect-  
ed to ground for supply voltages below 3.5V and left  
open for supply voltages above 3.5V.  
Figure 6 shows this connection. Higher frequency oper-  
ation lowers output impedance, reduces output ripple,  
allows the use of smaller capacitors, and shifts switch-  
ing noise out of the audio band. When the oscillator is  
driven externally, BOOST has no effect and should be  
left open. The BOOST pin should also be left open for  
normal operation.  
The MAX1044s LV pin can be grounded for all operat-  
ing conditions. The advantage is improved low-voltage  
performance and increased oscillator frequency. The  
d is a d va nta g e is inc re a s e d q uie s c e nt c urre nt a nd  
re d uc e d e ffic ie nc y a t hig he r s up p ly volta g e s . For  
Maxims ICL7660, the LV pin must be left open for  
supply voltages above 5V.  
Reducing the Oscillator Frequency Using C  
OSC  
An external capacitor can be connected to the OSC pin  
to lowe r the os c illa tor fre q ue nc y (Fig ure 6). Lowe r  
frequency operation improves efficiency at low load  
currents by reducing the ICs quiescent supply current.  
It also increases output ripple and output impedance.  
This can be offset by using larger values for C1 and C2.  
When operating at low supply voltages with LV open,  
connections to the LV, BOOST, and OSC pins should  
b e s hort or s hie ld e d to p re ve nt EMI from c a us ing  
oscillator jitter.  
Connections to the OSC pin should be short to prevent  
stray capacitance from reducing the oscillator frequency.  
Os c illa t o r Fre q u e n c y Co n s id e ra t io n s  
For normal operation, leave the BOOST and OSC pins  
of the MAX1044/ICL7660 open and use the nominal  
oscillator frequency. Increasing the frequency reduces  
audio interference, output resistance, voltage ripple,  
and required capacitor sizes. Decreasing frequency  
reduces quiescent current and improves efficiency.  
Overdriving the OSC Pin with an External Oscillator  
Driving OSC with an external oscillator is useful when  
the frequency must be synchronized, or when higher  
frequencies are required to reduce audio interference.  
The MAX1044/ICL7660 can be driven up to 400kHz.  
The pump and output ripple frequencies are one-half  
the e xte rna l c loc k fre q ue nc y. Driving the  
MAX1044/ICL7660 at a higher frequency increases the  
rip p le fre q ue nc y a nd a llows the us e of s ma lle r  
capacitors. It also increases the quiescent current.  
Oscillator Frequency Specifications  
The MAX1044/ICL7660 do not have a precise oscillator  
frequency. Only minimum values of 1kHz and 5kHz for  
the MAX1044 a nd a typ ic a l va lue of 10kHz for the  
ICL7660 are specified. If a specific oscillator frequency  
is required, use an external oscillator to drive the OSC  
pin.  
The OSC input threshold is V+ - 2.5V when V+ 5V,  
and is V+ / 2 for V+ < 5V. If the external clock does not  
swing all the way to V+, use a 10kpull-up resistor  
(Figure 7).  
Increasing Oscillator Frequency  
Using the BOOST Pin  
For the MAX1044, connecting the BOOST pin to the V+  
Ou t p u t Vo lt a g e Co n s id e ra t io n s  
The MAX1044/ICL7660 output voltage is not regulated.  
The output voltages will vary under load according to  
the output resistance. The output resistance is primarily  
pin raises the oscillator frequency by a factor of about 6.  
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