Datasheet

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LTC1261L

1261lfa

TYPICAL APPLICATION

FEATURES DESCRIPTION

Switched Capacitor

Regulated Voltage Inverter

The LT C

1261L is a switched-capacitor voltage inverter

designed to provide a regulated negative voltage from a

single positive supply. The LTC1261L operates from a

single 2.7V to 5.25V supply and provides an adjustable

output voltage from –1.23V to –5V. The LTC1261L-4/

LTC1261L-4.5 needs a single 4.5V to 5.25V supply and

provides a fixed output voltage of –4V to –4.5V respec-

tively. Three external capacitors are required: a 0.1µF flying

capacitor and an input and output bypass capacitors. An

optional compensation capacitor at ADJ (COMP) can be

used to reduce the output voltage ripple.

Each version of the LTC1261L will supply up to 20mA

output current with guaranteed output regulation of ±4.5%.

The LTC1261L includes an open-drain REG output that

pulls low when the output is within 5% of the set value.

Quiescent current is typically 650µA when operating and

5µA in shutdown.

The LTC1261L is available in 8-pin MSOP and SO packages.

APPLICATIONS

Regulated Negative Voltage from a

Single Positive Supply

REG Pin Indicates Output is in Regulation

Adjustable or Fixed Output Voltages

Output Regulation: ±4.5%

Supply Current: 650µA Typ

Shutdown Mode Drops Supply Current to 5µA

Up to 20mA Output Current

Requires Only Three or Four External Capacitors

Available in MS8 and SO-8 Packages

GaAs FET Bias Generators

Negative Supply Generators

Battery-Powered Systems

Single Supply Applications

L, LT , LT C , LT M, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

–4V Generator with Power Valid

LTC1261L-4

SHDN

REG

OUT

COMP

–

GND

0.1µF

1261L TA01

3.3µF

OUT

= –4V

AT 10mA

POWER VALID

1µF

10k

C3*

100pF

*OPTIONAL

Waveforms for –4V Generator with Power Valid

–4V

OUT

SHDN

0.1ms/DIV

1261L TA02

POWER VALID

Summary of content (14 pages)

PAGE 1
LTC1261L Switched Capacitor Regulated Voltage Inverter FEATURES n n n n n n n n n DESCRIPTION Regulated Negative Voltage from a Single Positive Supply REG Pin Indicates Output is in Regulation Adjustable or Fixed Output Voltages Output Regulation: ±4.
PAGE 2
LTC1261L ABSOLUTE MAXIMUM RATINGS (Note 1) Supply Voltage (Note 2)............................................5.5V Output Voltage (Note 3).............................0.3V to – 5.3V Total Voltage, VCC to VOUT (Note 2).........................10.8V SHDN Pin.......................................–0.3V to (VCC + 0.3V) REG Pin......................................................... –0.3V to 6V ADJ Pin..............................(VOUT – 0.3V) to (VCC + 0.3V) Output Short-Circuit Duration...................
PAGE 3
LTC1261L ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C, C1 = 0.1µF, COUT = 3.3µF unless otherwise noted. (Notes 2, 4) SYMBOL PARAMETER VCC CONDITIONS MIN Supply Voltage LTC1261LCMS8/LTC1261LCS8 LTC1261LCMS8-4/LTC1261LCS8-4 (Note 5) LTC1261LCMS8-4.5/LTC1261LCS8-4.5 (Note 5) l l l 2.7 4.35 4.75 VREF Reference Voltage ICC Supply Current VCC = 5.25V, No Load, SHDN Floating VCC = 5.
PAGE 4
LTC1261L TYPICAL PERFORMANCE CHARACTERISTICS Output Voltage vs Output Current 0 Output Voltage vs Output Current – 3.0 TA = 25°C VOUT = – 2V – 0.25 – 3.2 – 3.4 VCC = 2.7V –1.00 VCC = 4.5V – 3.5 – 3.6 –1.25 – 3.7 – 3.8 –1.50 VCC = 5V – 3.9 –1.75 VCC = 3V – 2.00 10 15 25 20 OUTPUT CURRENT (mA) – 4.2 30 –2.00 TA = 85°C –2.05 0 10 15 20 25 OUTPUT CURRENT (mA) 5 TA = – 40°C TA = 25°C – 4.00 TA = 85°C – 4.05 – 4.10 4.6 4.7 4.8 4.9 5.0 5.1 SUPPLY VOLTAGE (V) 5.2 80 5.2 70 4.8 4.
PAGE 5
LTC1261L TYPICAL PERFORMANCE CHARACTERISTICS Oscillator Frequency vs Temperature 0.6 675 650 625 600 575 0.5 VOUT = – 4V 0.4 0.3 VOUT = – 2V 0.2 0.1 550 525 –40 –25 –10 160 TA = 25°C IOUT = 10mA SHORT-CIRCUIT CURRENT (mA) 700 0.7 TA = 25°C VOUT = – 4V VCC = 5V START-UP TIME (ms) OSCILLATOR FREQUENCY (kHz) 725 5 20 35 50 65 TEMPERATURE (°C) Output Short-Circuit Current vs Temperature Start-Up Time vs Supply Voltage 80 95 0 140 120 100 3.0 3.5 4.5 4.0 SUPPLY VOLTAGE (V) 1261L G10 5.
PAGE 6
LTC1261L TEST CIRCUITS Adjustable Output Fixed Output 5V 1 + 10µF 0.1µF VCC SHDN 8 VCC 2 7 REG C1 + LTC1261L-X 3 6 OUT C1 – 4 GND COMP 5 1 VCC SHDN 8 2 VOUT = – 4V (LTC1261L-4) VOUT = – 4.5V (LTC1261L-4.5) + 3.3µF 1261L TCO1 0.1µF 7 REG C1 + LTC1261L 3 6 OUT C1 – 4 GND ADJ 5 VOUT + 3.3µF 1261L TCO2 APPLICATIONS INFORMATION The LTC1261L uses an inverting charge pump to generate a regulated negative output voltage that is either equal to or less than the supply voltage.
PAGE 7
LTC1261L APPLICATIONS INFORMATION VCC CLK 650kHz S1 OUT C1+ S C1 Q S2 R + R2 COUT S4 C1– R1 INTERNALLY CONNECTED FOR FIXED OUTPUT VOLTAGE PARTS S3 ADJ (COMP) + COMP1 REG + – COMP2 60mV – VREF = 1.23V 1261L F01 1.17V VOUT Figure 1. Block Diagram OUTPUT RIPPLE Output ripple in the LTC1261L is present from two sources; voltage droop at the output capacitor between clocks and frequency response of the regulation loop. Voltage droop is easy to calculate.
PAGE 8
LTC1261L APPLICATIONS INFORMATION increase the regulation loop bandwidth (Figure 2). This sounds counter intuitive until we remember that the internal reference is generated with respect to OUT, not ground. The feedback loop actually sees ground as its “output,” thus the compensation capacitor should be connected across the “top” of the resistor divider, from ADJ (or COMP) to ground. By the same token, avoid adding capacitance between ADJ (or COMP) and VOUT.
PAGE 9
LTC1261L APPLICATIONS INFORMATION tailored to the application. Reducing the value of the flying capacitor reduces the amount of charge transferred with each clock cycle. This limits maximum output current, but also cuts the size of the voltage step at the output with each clock cycle. The smaller capacitor draws smaller pulses of current out of VCC as well, limiting peak currents and reducing the demands on the input supply. Table 1 shows recommended values of flying capacitor vs maximum load capacity.
PAGE 10
LTC1261L APPLICATIONS INFORMATION The LTC1261L can be internally configured for other fixed output voltages. Contact the Linear Technology Marketing department for details. RESISTOR SELECTION Resistor selection is easy with the fixed output voltage versions of the LTC1261L—no resistors are needed! Selecting the right resistors for the adjustable parts is only a little more difficult. A resistor divider should be used to divide the signal at the output to give 1.
PAGE 11
LTC1261L TYPICAL APPLICATIONS 5V Input, – 0.5V Output GaAs FET Bias Generator P-CHANNEL POWER SWITCH VBAT SHUTDOWN 1 5V VCC SHDN 43.2k 1% 8 10k 2 1µF 0.1µF 7 REG C1+ LTC1261L 3 6 OUT C2– 4 ADJ GND –0.5V BIAS 12.4k 1% 5 + 3.3µF GaAs TRANSMITTER 100pF 1261 TA05 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. MS8 Package 8-Lead Plastic MSOP (Reference LTC DWG # 05-08-1660 Rev F) 0.889 ±0.127 (.035 ±.005) 5.23 (.
PAGE 12
LTC1261L PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610 Rev G) .050 BSC .189 – .197 (4.801 – 5.004) NOTE 3 .045 ±.005 8 .245 MIN .160 ±.005 .010 – .020 × 45° (0.254 – 0.508) NOTE: 1. DIMENSIONS IN 5 .150 – .157 (3.810 – 3.988) NOTE 3 1 RECOMMENDED SOLDER PAD LAYOUT .053 – .069 (1.346 – 1.752) 0°– 8° TYP .016 – .050 (0.406 – 1.
PAGE 13
LTC1261L REVISION HISTORY REV DATE DESCRIPTION A 9/12 Added I-grade option PAGE NUMBER Throughout Modified Output Regulation specifications 1, 3 Modified Package/Order Information tables 2 Modified Notes 4 and 5 4 1261lfa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use.
PAGE 14
LTC1261L TYPICAL APPLICATIONS Low Output Voltage Generator Minimum Parts Count – 4.5V Generator 5V 1µF 1 VCC 2 0.1µF 1 5V 100pF ADJ C1+ LTC1261L 3 C1– OUT GND 4 SHDN 8 2 RS 5 VCC 1µF 0.1µF 7 REG C1 + LTC1261L-4.5 3 6 OUT C1 – 4 124k GND COMP 5 VOUT = – 4.5V AT 5mA + 3.3µF 1261L TA07 6 1N5817 + VOUT = VCC – 9.92µA (RS + 124k) = – 0.5V (RS = 432k) = –1V (RS = 487k) 3.