Datasheet

ManualsBrandsTEXAS INSTRUMENTS ManualsPMICsPMIC - DC/DC voltage regulator Switched-capacitor voltage converter VSSOP 8

LM7705

RES

FLY

OUT

+ In

- In

shutdown

low voltage

amplifier

true zero

output voltage

-V

-0.23V

F+

OUT

RES

F-

LM7705

www.ti.com

SNVS420B –NOVEMBER 2008–REVISED MARCH 2013

LM7705 Low Noise Negative Bias Generator

Check for Samples: LM7705

FEATURES

DESCRIPTION

The LM7705 is a switched capacitor voltage inverter

• Regulated Output Voltage −0.232V

with a low noise, −0.23V fixed negative voltage

• Output Voltage Tolerance 5%

regulator. This device is designed to be used with low

• Output Voltage Ripple 4 mV

voltage amplifiers to enable the amplifiers output to

swing to zero volts. The −0.23 volts is used to supply

• Max Output Current 26 mA

the negative supply pin of an amplifier while

• Supply Voltage 3V to 5.25V

maintaining less then 5.5 volts across the amplifier.

• Conversion Efficiency up to 98%

Rail-to-Rail output amplifiers cannot output zero volts

when operating from a single supply voltage and can

• Quiescent Current 78 µA

result in error accumulation due to amplifier output

• Shutdown Current 20 nA

saturation voltage being amplified by following gain

• Turn on Time 500 µs

stages. A small negative supply voltage will prevent

the amplifiers output from saturating at zero volts and

• Operating Temperature Range −40°C to 125°C

will help maintain an accurate zero through a signal

• 8-Pin VSSOP Package

processing chain. Additionally, when an amplifier is

used to drive an ADC’s input, it can output a zero

APPLICATIONS

voltage signal and the full input range of an ADC can

• True Zero Amplifier Output be used. The LM7705 has a shutdown pin to

minimize standby power consumption

• Portable Instrumentation

• Low Voltage Split Power Supplies

Typical Application

These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam

during storage or handling to prevent electrostatic damage to the MOS gates.

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of

Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

2All trademarks are the property of their respective owners.

PRODUCTION DATA information is current as of publication date.

Products conform to specifications per the terms of the Texas

Instruments standard warranty. Production processing does not

necessarily include testing of all parameters.

Summary of content (22 pages)

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LM7705 www.ti.com SNVS420B – NOVEMBER 2008 – REVISED MARCH 2013 LM7705 Low Noise Negative Bias Generator Check for Samples: LM7705 FEATURES DESCRIPTION 1 • • • • • • • • • • • 2 Regulated Output Voltage −0.232V Output Voltage Tolerance 5% Output Voltage Ripple 4 mVPP Max Output Current 26 mA Supply Voltage 3V to 5.
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LM7705 SNVS420B – NOVEMBER 2008 – REVISED MARCH 2013 www.ti.com ABSOLUTE MAXIMUM RATINGS (1) (2) VALUE Supply Voltage VDD - VSS +5.75V SD VDD+0.3V, VSS-0.3V Human Body Model ESD Tolerance (3) For input pins only 2000V For all other pins 2000V Machine Model 200V Charged Device Model 750V −65°C to 150°C Storage Temp.
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LM7705 www.ti.com SNVS420B – NOVEMBER 2008 – REVISED MARCH 2013 3.3V Electrical Characteristics (continued) Unless otherwise specified, all limits are ensured for TA = 25°C, VDD = 3.3V, VSS = 0V, SD = 0V, CFLY= 5 µF, CRES = 22 µF, COUT = 22 µF. Boldface limits apply at temperature extremes (1). Symbol Parameter Conditions VIL Shutdown Input Low VIH Shutdown Input High IC Shutdown Pin Input Current SD = VDD Load Regulation 0 mA ≤ IOUT ≤ −20 mA Line Regulation 3V ≤ VDD ≤ 5.
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LM7705 SNVS420B – NOVEMBER 2008 – REVISED MARCH 2013 www.ti.
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LM7705 www.ti.com SNVS420B – NOVEMBER 2008 – REVISED MARCH 2013 Typical Performance Characteristics VDD = 3.3V and TA = 25°C unless otherwise noted. Output Voltage vs. Supply Voltage Supply Current vs. Supply Voltage 300 SUPPLY CURRENT (éA) OUTPUT VOLTAGE (V) -0.19 -0.20 -0.21 IOUT=10 mA IOUT = 20 mA -0.22 -0.23 250 200 125°C 85°C 150 25°C 100 50 0 -0.24 IOUT = 5 mA IOUT = 0 mA 3.0 3.5 4.0 4.5 SUPPLY VOLTAGE (V) -40°C 5.0 3.0 3.5 4.0 4.5 5.0 SUPPLY VOLTAGE (V) Figure 1. Figure 2.
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LM7705 SNVS420B – NOVEMBER 2008 – REVISED MARCH 2013 www.ti.com Typical Performance Characteristics (continued) VDD = 3.3V and TA = 25°C unless otherwise noted. Supply Current vs. Output Current Supply Current vs. Output Current SUPPLY VOLTAGE = 5.0V SUPPLY VOLTAGE = 3.3V 20 SUPPLY CURRENT (mA) 16 -40°C 12 25°C 8 85°C 4 0 16 -40°C 12 25°C 8 0 125°C 0 4 85°C 4 8 12 16 20 125°C 0 4 20 Current Conversion Efficiency vs. Output Current Current Conversion Efficiency vs.
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LM7705 www.ti.com SNVS420B – NOVEMBER 2008 – REVISED MARCH 2013 Typical Performance Characteristics (continued) VDD = 3.3V and TA = 25°C unless otherwise noted. Load Regulation vs. Temperature SUPPLY VOLTAGE = 3.3V SUPPLY VOLTAGE = 5.0V 0.4 LOAD REGULATION (%/mA) 0.4 0.3 0.2 0.1 0.0 0.3 0.2 0.1 0.0 0 40 80 120 -40 0 40 Figure 13. Transient Response SUPPLY VOLTAGE = 3.3V 30 -0.226 20 +85/+125°C 10 OUTPUT VOLTAGE (V) -40°C -0.218 -0.234 0 -0.242 30 -0.226 20 +25°C 10 0 -0.
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LM7705 SNVS420B – NOVEMBER 2008 – REVISED MARCH 2013 www.ti.com Typical Performance Characteristics (continued) VDD = 3.3V and TA = 25°C unless otherwise noted. Output voltage vs. shutdown Voltage Supply Current vs. Shutdown Voltage 300 SUPPLY VOLTAGE = 5V 0 -0.05 SUPPLY CURRENT (éA) OUTPUT VOLTAGE (V) 250 SUPPLY VOLTAGE = 3.3V -0.10 -0.15 SUPPLY VOLTAGE = 5V -0.20 200 150 SUPPLY VOLTAGE = 3.3V 100 50 -0.
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LM7705 www.ti.com SNVS420B – NOVEMBER 2008 – REVISED MARCH 2013 APPLICATION INFORMATION This applications section will give a description of the functionality of the LM7705. The LM7705 is a switched capacitor voltage inverter with a low noise, −0.23V fixed negative bias output. The part will operate over a supply voltage range of 3 to 5.25 Volt. Applying a logical low level to the SD input will activate the part, and generate a fixed −0.23V output voltage.
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LM7705 SNVS420B – NOVEMBER 2008 – REVISED MARCH 2013 • • www.ti.com Controlling the power supplied from the power supply to the charge pump input by the pre-regulator The power supplied from the charge pump output to the load by the post-regulator. A more detailed block diagram of the negative bias generator is given in Figure 24. The control of the preregulator is based on measuring the output voltage of the charge pump.
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LM7705 www.ti.com SNVS420B – NOVEMBER 2008 – REVISED MARCH 2013 REQ V2 V1 CRES RL Figure 26.
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LM7705 SNVS420B – NOVEMBER 2008 – REVISED MARCH 2013 www.ti.com OUTPUT VOLTAGE (V) V+ OUTPUT SATURATION VDSAT 0 0 V+ INPUT VOLTAGE (V) Figure 27. Limitation of the Output of an Amplifier The introduction of operational amplifiers with output Rail-to-rail drive capabilities is a strong improvement and the (output) performance of op amps is for many applications no longer a limiting factor.
PAGE 13
LM7705 www.ti.com SNVS420B – NOVEMBER 2008 – REVISED MARCH 2013 The sensor has a DC output signal that is amplified by the op amp. For an optimal output voltage swing of the op amp should be matched to the input voltage range Converter (ADC). For the high side of the range this can be done by adjusting the gain the low side of the range can’t be adjusted and is affected by the output swing of the op signal-to-noise ratio, the of the Analog to Digital of the op amp. However, amp.
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LM7705 SNVS420B – NOVEMBER 2008 – REVISED MARCH 2013 www.ti.com Dual Supply, True Zero Amplifiers The limitations of the output stage of the op amp, as indicated in both examples, can be omitted by using a dual supply op amp. The output stage of the used op amp can then still swing from 50 mV of the supply rails. However, the functional output range of the op amp is now from ground level to a value near the positive supply rail.
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LM7705 www.ti.com SNVS420B – NOVEMBER 2008 – REVISED MARCH 2013 VREF +V LMP7701 VIN ADC122S021 + ADC SDO - CRES -V A B +V LM7705 COUT CFLY Figure 32. Typical True Zero Output Voltage Application with/without LM7705 The output voltage of the LMP7701 is converted to the digital domain using an ADC122S021. This is an 12 bit analog to digital converter with a serial data output. Data processing and graphical displaying is done with a computer.
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LM7705 SNVS420B – NOVEMBER 2008 – REVISED MARCH 2013 www.ti.com 0.050 DIGITIZED OUTPUT VOLTAGE (V) DIGITIZED OUTPUT VOLTAGE (`V) 0.050 0.040 0.030 0.020 0.010 0.040 0.030 0.020 0.010 VDSAT 0.000 0 80 160 240 320 0.000 0 400 TIME (SAMPLES) A 80 160 240 320 400 TIME (SAMPLES) B Figure 33. Digitized Output Voltage without (A) and with (B) LM7705 Figure 33A shows the digitized output voltage of the op amp when its negative supply pin is connected to ground level.
PAGE 17
LM7705 www.ti.com SNVS420B – NOVEMBER 2008 – REVISED MARCH 2013 REVISION HISTORY Changes from Revision A (March 2013) to Revision B • Page Changed layout of National Data Sheet to TI format ..........................................................................................................
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PACKAGE OPTION ADDENDUM www.ti.
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PACKAGE MATERIALS INFORMATION www.ti.com 26-Mar-2013 TAPE AND REEL INFORMATION *All dimensions are nominal Device Package Package Pins Type Drawing LM7705MM/NOPB VSSOP DGK 8 LM7705MME/NOPB VSSOP DGK LM7705MMX/NOPB VSSOP DGK SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant 1000 178.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1 8 250 178.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1 8 3500 330.0 12.4 5.3 3.4 1.4 8.0 12.
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PACKAGE MATERIALS INFORMATION www.ti.com 26-Mar-2013 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LM7705MM/NOPB VSSOP DGK 8 1000 210.0 185.0 35.0 LM7705MME/NOPB VSSOP DGK 8 250 210.0 185.0 35.0 LM7705MMX/NOPB VSSOP DGK 8 3500 367.0 367.0 35.
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