MAX749 Maxim Integrated Products, MAX749 Datasheet
MAX749
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MAX749 Summary of contents
Page 1
... Quiescent current is only 60µA max and is reduced to under 15µA in shutdown mode. While shut down, the MAX749 retains the voltage set point, simpli- fying software control. The MAX749 drives either an external P-channel MOSFET or a PNP transistor. ...
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... Minimum ADJ High Pulse Width t SH Minimum ADJ Low Pulse Width t Minimum ADJ Low to CTRL Low ______________________________________________________________________________________ Operating Temperature Ranges: MAX749C_A........................................................0°C to +70°C MAX749E_A .....................................................-40°C to +85°C Storage Temperature Range .............................-65°C to +160°C Lead Temperature (soldering, 10sec) .............................+300°C CONDITIONS On power-up or reset (Note ...
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Digitally Adjustable LCD Bias Supply __________________________________________Typical Operating Characteristics (T = +25° 47µH, unless otherwise noted.) A EFFICIENCY vs. OUTPUT CURRENT – PNP 85 80 -12V -24V - 470 BASE R = 0.25 ...
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... ADJ low, the counter is reset to mid-scale when ADJ is high. When ADJ is low, the counter does not change (regardless of activity on CTRL) as long applied. Logic Input. When CTRL and ADJ are low, the MAX749 is shut down, but the counter is not reset. 3 CTRL When CTRL is low, the counter is reset to mid-scale when ADJ is high. The device is always on when CTRL is high ...
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... MAX749 may also be operated from the regulat- ed +5V supply. A high-efficiency +5V regulator, such as the MAX782 ideal source for the MAX749. In this example, the MAX749 efficiency (80%) is compounded with the MAX782 efficiency (95%): 80% x 95% = 76%, which is still high ...
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... MAXIMUM ON-TIME ONE-SHOT TRIG Q REF MAX749 Figure 2. Switch-Mode Power-Supply Section Block Diagram Once turned off, a one-shot holds the switch off for a minimum of 1µs, and the switch either stays off (if the output is in regulation), or turns on again (if the output is out of regulation). With light loads, the transistor switches for one or more cycles and then turns off, much like a traditional PFM converter ...
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... SHUTDOWN RESET Figure 6. Reset Sequence with Shutdown _______________________________________________________________________________________ In Figure 3, the MAX749 is reset when it is taken out of shutdown, which sets the output at mid-scale. Figure 4 shows how to increment the counter. Figure 5 illustrates a reset without shutting the device down. Figure 7 provides an example of a sequence of opera- ...
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... PWM Adjustment A positive pulse-width modulated (PWM) logic signal (e.g., from a microcontroller) can control the MAX749’s output voltage. Use the PWM signal to pull up the FB pin through a suitable resistor network on the PWM output would also be required. In this configura- tion, the longer the PWM signal remains high, the more negative the MAX749’ ...
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... Current-Sense Resistor section). However, because the current is limited by the MAX749, the inductor can safely be driven into satura- tion with only a slight impact on efficiency. For highest efficiency, use a coil with low resistance, preferably under 300mΩ ...
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... I -V OUTMAX External Switching Transistor The MAX749 can drive a PNP transistor or a P-channel logic-level MOSFET. The choice of a power switch is dictated by the input voltage range, cost, and efficiency. MOSFETs provide the highest efficiency because they do not draw any DC gate-drive current (see Typical Operating Characteristics graphs) ...
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... Use a star ground configuration: Connect the ground lead of the input bypass capacitor, the output capaci- tor, and the inductor at a common point next to the GND pin of the MAX749. Additionally, connect the posi- tive lead of the input bypass capacitor as close as pos- sible to the V+ pin of the IC. ...
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Digitally Adjustable LCD Bias Supply _______________________________________________________Package Information ______________________________________________________________________________________ 0° - 15° Plastic DIP PKG. PLASTIC P P ...