Datasheet

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LTC3260

3260fa

Typical applicaTion

FeaTures DescripTion

Low Noise Dual Supply

Inverting Charge Pump

The LT C

3260 is a low noise dual polarity output power

supply that includes an inverting charge pump with both

positive and negative LDO regulators. The charge pump

operates over a wide 4.5V to 32V input range and can deliver

up to 100mA of output current. Each LDO regulator can

provide up to 50mA of output current. The negative LDO

post regulator is powered from the charge pump output.

The LDO output voltages can be adjusted using external

resistor dividers.

The charge pump employs either low quiescent current

Burst Mode operation or low noise constant frequency

mode. In Burst Mode operation the charge pump V

OUT

regulates to –0.94 • V

, and the LTC3260 draws only

100µA of quiescent current with both LDO regulators on.

In constant frequency mode the charge pump produces

an output equal to –V

and operates at a fixed 500kHz

or to a programmed value between 50kHz to 500kHz us-

ing an external resistor. The LTC3260 is available in low

profile (0.75mm) 3mm x 4mm 14-pin DFN and thermally

enhanced 16-pin MSOP packages.

±12V Outputs from a Single 15V Input

LDO Rejection of V

OUT

Ripple

applicaTions

Range: 4.5V to 32V

Inverting Charge Pump Generates –V

Charge Pump Output Current Up to 100mA

Low Noise Negative LDO Post Regulator

LDO

–

= 50mA Max)

Low Noise Independent Positive LDO Regulator

LDO

= 50mA Max)

100µA Quiescent Current in Burst Mode

Operation

with Both LDO Regulators On

50kHz to 500kHz Programmable Oscillator Frequency

Stable with Ceramic Capacitors

Short-Circuit/Thermal Protection

Low Profile 3mm × 4mm 14-Pin DFN and Thermally

Enhanced 16-Pin MSOP Packages

Low Noise Bipolar/Inverting Supplies

Industrial/Instrumentation Low Noise Bias

Generators

Portable Medical Equipment

Portable Instruments

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

and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the

property of their respective owners.

10µF10µF

1µF

10nF

10µF10µF

909k

200k

100k

12V

–12V

3260 TA01a

LDO

15V

LDO

–

ADJ

LTC3260

ADJ

–

GND

BYP

–

OUT

–15V

–

MODE

–

LDO

10mV/DIV

AC-COUPLED

LDO

–

10mV/DIV

AC-COUPLED

OUT

10mV/DIV

AC-COUPLED

1µs/DIV

3260 TA01b

= 15V

LDO

= 12V

LDO

–

= –12V

OSC

= 500kHz

LDO

= 50mA

LDO

–

–50mA

Summary of content (18 pages)

PAGE 1
LTC3260 Low Noise Dual Supply Inverting Charge Pump Features n n n n n n n n n n Description VIN Range: 4.
PAGE 2
LTC3260 Absolute Maximum Ratings (Notes 1, 3) VIN, EN+, EN–, MODE.................................. –0.3V to 36V LDO+ ............................................................–16V to 36V VOUT, LDO – ................................................ –36V to 0.3V RT, ADJ+....................................................... –0.3V to 6V BYP+.......................................................... –0.3V to 2.5V ADJ –............................................................. –6V to 0.3V BYP–..........
PAGE 3
LTC3260 Electrical Characteristics The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VIN = EN+ = EN– = 12V, MODE = 0V, RT = 200kΩ.
PAGE 4
LTC3260 Electrical Characteristics Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LTC3260 is tested under pulsed load conditions such that TJ ≈ TA. The LTC3260E is guaranteed to meet specifications from 0°C to 85°C junction temperature.
PAGE 5
LTC3260 Typical Performance Characteristics (TA = 25°C, CFLY = 1µF, CIN = COUT = CLDO+ = CLDO– = 10µF unless otherwise noted) Effective Open-Loop Resistance vs Temperature 250 50 40 30 20 VIN = 32V VIN = 25V VIN = 12V 10 0 –50 –25 0 200 100 RT = 200kΩ 50 0 5 20 10 25 15 SUPPLY VOLTAGE (V) 800 fOSC = 500kHz 30 20 1.212 1.200 1.188 0 5 10 15 20 25 SUPPLY VOLTAGE (V) 30 35 1.176 –50 –25 0 700 100 3260 G09 VIN = 12V ILDO+ = 50mA 600 500 400 300 200 60 0.14 LDO+ Load Regulation 1.
PAGE 6
LTC3260 Typical Performance Characteristics + – (TA = 25°C, CFLY = 1µF, CIN = COUT = CLDO = CLDO = 10µF unless otherwise noted) LDO– Dropout Voltage vs Temperature ADJ– Pin Voltage vs Temperature 60 400 –1.188 –1.200 –1.212 VOUT = –12V – 350 ILDO = 50mA LDO– SUPPLY REJECTION (dB) LDO– DROPOUT VOLTAGE (mV) –1.176 ADJ– PIN VOLTAGE (V) LDO– Power Supply Rejection 300 250 200 150 100 50 –1.224 –50 –25 0 0 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 0 VOUT = –12V UNITY GAIN VLDO– (V) –1.
PAGE 7
LTC3260 Pin Functions (DFN/MSOP) EN+ (Pin 1/ Pin 1): Logic Input. A logic “high” on the EN+ pin enables the positive low dropout (LDO+) regulator. RT (Pin 2/Pin 2): Input Connection for Programming the Switching Frequency. The RT pin servos to a fixed 1.2V when the EN– pin is driven to a logic “high”. A resistor from RT to GND sets the charge pump switching frequency. If the RT pin is tied to GND, the switching frequency defaults to a fixed 500kHz. BYP– (Pin 3/ Pin 3): LDO– Reference Bypass Pin.
PAGE 8
LTC3260 Block Diagram Note: Pin numbers are as per DFN package. Refer to the Pin Functions section for corresponding MSOP pin numbers. 1 EN+ INVERTING CHARGE PUMP 9 LDO+ VIN S1 8 7 C+ S3 C– S2 – + S4 11 12 RT EN– MODE BYP+ 1.2V REF 50kHz TO 500kHz OSC BYP– –1.2V REF ADJ– – 2 VOUT CHARGE PUMP AND INPUT LOGIC LDO– 15 13 14 3 4 + 6 ADJ+ 10 5 GND Operation (Refer to the Block Diagram) The LTC3260 is a high voltage low noise dual output regulator.
PAGE 9
LTC3260 Operation (Refer to the Block Diagram) The charge transfer frequency can be adjusted between 50kHz and 500kHz using an external resistor on the RT pin. At slower frequencies the effective open-loop output resistance (ROL) of the charge pump is larger and it is able to provide smaller average output current. Figure 1 can be used to determine a suitable value of RT to achieve a required oscillator frequency. If the RT pin is grounded, the part operates at a constant frequency of 500kHz.
PAGE 10
LTC3260 Operation (Refer to the Block Diagram) Figure 2 shows the LDO+ regulator application circuit. The LDO+ output voltage VLDO+ can be programmed by choosing suitable values of R1 and R2 such that:  R1  VLDO+ = 1.2V •  + 1  R2  An optional capacitor of 10nF can be connected from the BYP+ pin to ground. This capacitor bypasses the internal 1.2V reference of the LTC3260 and improves the noise performance of the LDO+. If this function is not used the BYP+ pin should be left floating.
PAGE 11
LTC3260 Applications Information Effective Open-Loop Output Resistance The effective open-loop output resistance (ROL) of a charge pump is a very important parameter which determines the strength of the charge pump. The value of this parameter depends on many factors such as the oscillator frequency (fOSC), value of the flying capacitor (CFLY), the nonoverlap time, the internal switch resistances (RS) and the ESR of the external capacitors.
PAGE 12
LTC3260 Applications Information also have a poor voltage coefficient causing them to lose 60% or more of their capacitance when the rated voltage is applied. Therefore when comparing different capacitors, it is often more appropriate to compare the amount of achievable capacitance for a given case size rather than discussing the specified capacitance value. The capacitor manufacture’s data sheet should be consulted to ensure the desired capacitance at all temperatures and voltages.
PAGE 13
LTC3260 Applications Information MAXIMUM POWER DISSIPATION (W) 6 The derating curve in Figure 6 assumes a maximum thermal resistance, θJA, of 43°C/W for the package. This can be achieved with a four layer PCB that includes 2oz Cu traces and six vias from the exposed pad of the LTC3260 to the ground plane. θJA = 43°C/W 5 4 3 2 1 It is recommended that the LTC3260 be operated in the region corresponding to TJ ≤ 150°C for continuous operation as shown in Figure 6.
PAGE 14
LTC3260 Typical Applications 28V Dual Tracking Bipolar Supply with Outputs from ±5V to ±25V 28V 11 C1 4.7µF 50V C2 1µF 50V 1 VIN 14 2 12 ADJ+ 15 EN+ 13 EN– 10 + C 7 LDO+ BYP+ 16 C4 0.01µF LTC3260 4 ADJ– 3 – BYP C– MODE LDO– RT VOUT GND 17 R1 732k C5 0.01µF C7 4.7µF 50V OUT R2 73.2k R3 500k R4 732k 5 6 C3 4.7µF 35V C6 4.
PAGE 15
LTC3260 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DE Package 14-Lead Plastic DFN (4mm × 3mm) (Reference LTC DWG # 05-08-1708 Rev B) 4.00 ±0.10 (2 SIDES) R = 0.05 TYP 0.70 ±0.05 3.60 ±0.05 2.20 ±0.05 3.30 ±0.05 PACKAGE OUTLINE PIN 1 TOP MARK (SEE NOTE 6) 1.70 ±0.05 0.25 ±0.05 0.50 BSC 0.200 REF 3.00 ±0.10 (2 SIDES) 0.75 ±0.05 R = 0.115 TYP 8 0.40 ±0.10 14 3.30 ±0.10 1.70 ±0.10 PIN 1 NOTCH R = 0.20 OR 0.
PAGE 16
LTC3260 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. MSE Package 16-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1667 Rev E) BOTTOM VIEW OF EXPOSED PAD OPTION 2.845 ±0.102 (.112 ±.004) 5.23 (.206) MIN 2.845 ±0.102 (.112 ±.004) 0.889 ±0.127 (.035 ±.005) 8 1 1.651 ±0.102 (.065 ±.004) 1.651 ±0.102 3.20 – 3.45 (.065 ±.004) (.126 – .136) 0.305 ±0.038 (.0120 ±.0015) TYP 16 0.50 (.0197) BSC 4.039 ±0.102 (.159 ±.
PAGE 17
LTC3260 Revision History REV DATE DESCRIPTION A 09/12 Changed Operating Junction Temperature. PAGE NUMBER Add H- and MP-grade options. 2 Throughout Add Junction to heading of Electrical Characteristics table. 3 Add H- and MP-grade into Note 2. 4 Modified Shutdown Current vs Temperature curve for operation to 150°C. 4 Modified Quiescent Current vs Temperature curve for operation to 150°C. 4 Corrected Figure 5 Pinout RT and CBYP. 12 Removed Thermal Shutdown curve from Figure 6.
PAGE 18
LTC3260 Typical Application Low Noise ±12V Power Supply from a Single-Ended 15V Input Supply (Frequency = 200kHz) 9 15V C1 10µF 1 11 12 C2 1µF 8 7 6 C3 10µF LDO+ VIN LTC3260 EN+ ADJ+ EN– BYP+ MODE GND C+ BYP– 10 13 14 C4 10µF 15 C5 10nF 3 C6 10nF 4 ADJ– C– VOUT LDO – 2 R5 200k R1 909k R2 100k R3 100k R4 909k 5 RT 12V C7 10µF 3260 TA03 –12V Related Parts PART NUMBER DESCRIPTION COMMENTS LTC1144 Switched-Capacitor Wide Input Range Voltage Converter with Shutdown Wide I