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LM7705

LM7705 Low Noise Negative Bias Generator

Literature Number: SNVS420A

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Summary of Contents for LM7705

Page 1: ...LM7705 LM7705 Low Noise Negative Bias Generator Literature Number SNVS420A ...

Page 2: ...l prevent the amplifiers output from saturating at zero volts and will help maintain an accurate zero through a signal processing chain Additionally when an amplifier is used to drive an ADC s input it can output a zero voltage sig nal and the full input range of an ADC can be used The LM7705 has a shutdown pin to minimize standby power con sumption Features Regulated output voltage 0 232V Output ...

Page 3: ...V CFLY 5 µF CRES 22 µF COUT 22 µF Boldface limits apply at temperature extremes Note 5 Symbol Parameter Conditions Min Note 6 Typical Note 7 Max Note 6 Units VOUT Output Voltage IOUT 0 mA 0 242 0 251 0 232 0 219 0 209 V IOUT 20 mA 0 242 0 251 0 226 0 219 0 209 VR Output Voltage Ripple IOUT 20 mA 4 mVPP IS Supply Current No Load 50 78 100 150 μA ISD Shutdown Supply Current SD VDD 20 nA ηPOWER Curre...

Page 4: ...ditions for which the device is intended to be functional but specific performance is not guaranteed For guaranteed specifications and test conditions see the Electrical Characteristics Note 2 Human Body Model applicable std MIL STD 883 Method 3015 7 Machine model applicable std JESD22 A115 A ESSD MM srd of JEDEC Field induced Charge Device Model applicable std JESD22 C101 C ESD FICDM std of JEDEC...

Page 5: ...vice is OFF 4 VDD Positive Supply Voltage 5 VSS Power Ground 6 VOUT Output Voltage 7 CRES Reserve Capacitor Connection 8 CF CFLY Negative Capacitor Connection Ordering Information Package Part Number Package Marking Transport Media NSC Drawing 8 Pin MSOP LM7705MM F26A 1k Units Tape and Reel MUA08A LM7705MME 250 Units Tape and Reel LM7705MMX 3 5k Units Tape and Reel Block Diagram 20173003 LM7705 ww...

Page 6: ...tput Voltage vs Supply Voltage 20173010 Supply Current vs Supply Voltage 20173011 Output Voltage vs Output Current 20173012 Output Voltage vs Output Current 20173013 Output Voltage Ripple vs Temperature 20173014 Output Voltage Ripple vs Temperature 20173015 5 www national com LM7705 ...

Page 7: ...20173016 Supply Current vs Output Current 20173017 Current Conversion Efficiency vs Output Current 20173018 Current Conversion Efficiency vs Output Current 20173019 Turn On Time 20173020 Turn On Time 20173021 www national com 6 LM7705 ...

Page 8: ...ulation vs Temperature 20173022 Load Regulation vs Temperature 20173023 Transient Response 20173024 Transient Response 20173025 Transient Response 20173029 Transient Response 20173030 7 www national com LM7705 ...

Page 9: ...Output voltage vs shutdown Voltage 20173026 Supply Current vs Shutdown Voltage 20173027 Oscillator Frequency vs Temperature 20173028 www national com 8 LM7705 ...

Page 10: ...ipple can be influenced by changing the values of the used capacitors In the next section a more detailed technical description of the LM7705 will be given TECHNICAL DESCRIPTION As indicated in the functional description section the main function of the LM7705 is to supply a stabilized negative bias voltage to a load using only a positive supply voltage A gen eral block diagram for this charge pum...

Page 11: ...rt Output Voltage Line Regulation The fixed and regulated output voltage of 0 23 V has tight limits as indicated in the Electrical Characteristics table to guar antee a stable voltage level The usage of the pre and post regulator in combination with the charge pump inverter ensures good line regulation of 0 29 V Output current Load regulation The LM7705 can sink currents 26 mA causing an output vo...

Page 12: ...URE 8 Sensor with DC Output and a Single Supply Op Amp The sensor has a DC output signal that is amplified by the op amp For an optimal signal to noise ratio the output voltage swing of the op amp should be matched to the input voltage range of the Analog to Digital Converter ADC For the high side of the range this can be done by adjusting the gain of the op amp However the low side of the range c...

Page 13: ...r output drive with a dual supply Disadvantages of this solution are The usage of a dual supply instead of a simple single supply is more expensive A dual supply voltage for the op amps requires parts that can handle a larger operating range for the supply voltage If the op amps used in the current solution can t handle this a redesign can be required A better solution is to use the LM7705 This lo...

Page 14: ... fluctuations 1 bit quantization error Figure 12B show the digitized output voltage of the op amp when its negative supply pin is connected to the output of the LM7705 Again the graph shows some 1 bit quantization er rors caused by the voltage ripple and output noise In this case the op amps output level can reach the true zero output level The graphs in Figure 12 show that With a single supply th...

Page 15: ...Physical Dimensions inches millimeters unless otherwise noted 8 Pin MSOP NS Package Number MUA08A www national com 14 LM7705 ...

Page 16: ...Notes 15 www national com LM7705 ...

Page 17: ...ODUCT IS NOT NECESSARILY PERFORMED NATIONAL ASSUMES NO LIABILITY FOR APPLICATIONS ASSISTANCE OR BUYER PRODUCT DESIGN BUYERS ARE RESPONSIBLE FOR THEIR PRODUCTS AND APPLICATIONS USING NATIONAL COMPONENTS PRIOR TO USING OR DISTRIBUTING ANY PRODUCTS THAT INCLUDE NATIONAL COMPONENTS BUYERS SHOULD PROVIDE ADEQUATE DESIGN TESTING AND OPERATING SAFEGUARDS EXCEPT AS PROVIDED IN NATIONAL S TERMS AND CONDITI...

Page 18: ...for use in safety critical applications such as life support where a failure of the TI product would reasonably be expected to cause severe personal injury or death unless officers of the parties have executed an agreement specifically governing such use Buyers represent that they have all necessary expertise in the safety and regulatory ramifications of their applications and acknowledge and agre...

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