LTC3260IDE - LINEAR TECHNOLOGY

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 VOUT

regulates to –0.94 • VIN, 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 –VIN 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 VOUT Ripple

applicaTions

n VIN Range: 4.5V to 32V

n Inverting Charge Pump Generates –VIN

n Charge Pump Output Current Up to 100mA

n Low Noise Negative LDO Post Regulator

(ILDO– = 50mA Max)

n Low Noise Independent Positive LDO Regulator

(ILDO+ = 50mA Max)

n 100µA Quiescent Current in Burst Mode

Operation

with Both LDO Regulators On

n 50kHz to 500kHz Programmable Oscillator Frequency

n Stable with Ceramic Capacitors

n Short-Circuit/Thermal Protection

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

Enhanced 16-Pin MSOP Packages

n Low Noise Bipolar/Inverting Supplies

n Industrial/Instrumentation Low Noise Bias

Generators

n Portable Medical Equipment

n 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+

BYP–

VIN

VOUT

–15V

EN+

C–

MODE

EN–

C+

VLDO+

10mV/DIV

AC-COUPLED

VLDO–

10mV/DIV

AC-COUPLED

VOUT

10mV/DIV

AC-COUPLED

1µs/DIV 3260 TA01b

VIN = 15V

VLDO+ = 12V

VLDO– = –12V

fOSC = 500kHz

ILDO+ = 50mA

ILDO– –50mA

LTC3260

3260fa

absoluTe MaxiMuM raTings

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– ......................................................... –2.5V to 0.3V

(Notes 1, 3)

BYP+

ADJ+

MODE

EN–

LDO+

VIN

C+

EN+

BYP–

ADJ–

LDO–

VOUT

C–

TOP VIEW

GND

DE PACKAGE

14-LEAD (4mm × 3mm) PLASTIC DFN

TJMAX = 150°C, θJA = 43°C/W

EXPOSED PAD (PIN 15) IS GND, MUST BE SOLDERED TO PCB

EN+

BYP–

ADJ–

LDO–

VOUT

C–

BYP+

ADJ+

MODE

EN–

LDO+

VIN

C+

TOP VIEW

MSE PACKAGE

16-LEAD PLASTIC MSOP

GND

TJMAX = 150°C, θJA = 43°C/W

EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB

pin conFiguraTion

orDer inForMaTion

LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LTC3260EDE#PBF LTC3260EDE#TRPBF 3260 14-Lead (4mm × 3mm) Plastic DFN –40°C to 125°C

LTC3260IDE#PBF LTC3260IDE#TRPBF 3260 14-Lead (4mm × 3mm) Plastic DFN –40°C to 125°C

LTC3260EMSE#PBF LTC3260EMSE#TRPBF 3260 16-Lead Plastic MSOP –40°C to 125°C

LTC3260IMSE#PBF LTC3260IMSE#TRPBF 3260 16-Lead Plastic MSOP –40°C to 125°C

LTC3260HMSE#PBF LTC3260HMSE#TRPBF 3260 16-Lead Plastic MSOP –40°C to 150°C

LTC3260MPMSE#PBF LTC3260MPMSE#TRPBF 3260 16-Lead Plastic MSOP –55°C to 150°C

Consult LT C Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping

container.Consult LT C Marketing for information on non-standard lead based finish parts.

For more information on lead free part marking, go to: http://www.linear.com/leadfree/

For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/

VOUT, LDO+, LDO– Short-Circuit Duration ........ Indefinite

Operating Junction Temperature Range

(Note 2) .................................................. –55°C to 150°C

Storage Temperature Range ................. –65°C to 150°C

Lead Temperature (Soldering, 10 sec)

MSE Only ..........................................................300°C

LTC3260

3260fa

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.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Charge Pump

VIN Input Voltage Range l4.5 32 V

VUVLO VIN Undervoltage Lockout Threshold VIN Rising

VIN Falling

3.4

3.8

3.6

4 V

IVIN VIN Quiescent Current Shutdown, EN+ = EN– = 0V

EN– = 0V, ILDO+ = 0mA

MODE = VIN, EN+ = 0V, IVOUT = ILDO– = 0mA

MODE = VIN, IVOUT = ILDO+ = ILDO– = 0mA

MODE = 0V, IVOUT = 0mA

100

3.5

160

200

5.5

µA

VRT RT Regulation Voltage 1.200 V

VOUT VOUT Regulation Voltage MODE = 12V

MODE = 0V

–0.94 • VIN

–VIN

fOSC Oscillator Frequency RT = GND 450 500 550 kHz

ROUT Charge Pump Output Impedance MODE = 0V, RT = GND 32 Ω

ISHORT_CKT Max IVOUT Short-Circuit Current VOUT = GND l100 160 250 mA

VMODE(H) MODE Threshold Rising l1.1 2.0 V

VMODE(L) MODE Threshold Falling l0.4 1.0 V

IMODE MODE Pin Internal Pull-Down Current VIN = MODE = 32V 0.7 µA

50mA Positive Regulator

LDO+ Output Voltage Range l1.2 32 V

VADJ+ADJ+ Reference Voltage l1.176 1.200 1.224 V

IADJ+ADJ+ Input Current VADJ+ = 1.2V –50 50 nA

ILDO+(SC) LDO+ Short-Circuit Current l50 100 mA

Line Regulation 0.04 mV/V

Load Regulation 0.03 mV/mA

VDROPOUT+LDO+ Dropout Voltage ILDO+ = 50mA 400 800 mV

Output Voltage Noise CBYP+ = 10nF 100 µVRMS

VEN+(H) EN+ Threshold Rising l1.1 2.0 V

VEN+(L) EN+ Threshold Falling l0.4 1.0 V

IEN+EN+ Pin Internal Pull-Down Current VIN = EN+ = 32V 0.7 µA

50mA Negative Regulator

LDO– Output Voltage Range l–32 –1.2 V

VADJ–ADJ– Reference Voltage l–1.224 –1.200 –1.176 V

IADJ–ADJ– Input Current VADJ– = –1.2V –50 50 nA

ILDO–(SC) LDO– Short-Circuit Current l50 100 mA

Line Regulation 0.002 mV/V

Load Regulation 0.02 mV/mA

VDROPOUT–LDO– Dropout Voltage ILDO– = 50mA 200 500 mV

Output Voltage Noise CBYP– = 10nF 100 µVRMS

VEN(H) EN– Threshold Rising l1.1 2.0 V

VEN(L) EN– Threshold Falling l0.4 1.0 V

IEN–EN– Pin Internal Pull-Down Current VIN = EN– = 32V 1.4 µA

LTC3260

3260fa

Typical perForMance characTerisTics

Oscillator Frequency

vs Supply Voltage Oscillator Frequency vs RTShutdown Current vs Temperature

Quiescent Current vs Temperature

Quiescent Current vs Supply

Voltage (Constant Frequency Mode)

Quiescent Current vs Temperature

(Constant Frequency Mode)

(TA = 25°C, CF LY = 1µF, CIN = COUT = CLDO+ = CLDO– = 10µF unless otherwise noted)

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. Specifications over the –40°C to

125°C operating junction temperature range are assured by design,

characterization and correlation with statistical process controls. The

LTC3260I is guaranteed over the –40°C to 125°C operating junction

temperature range, the LTC3260H is guaranteed over the –40°C to 150°C

operating junction temperature range and the LTC3260MP is tested and

guaranteed over the full –55°C to 150°C operating junction temperature

range. Note that the maximum ambient temperature consistent with

these specifications is determined by specific operating conditions in

conjunction with board layout, the rated package thermal impedance and

other environmental factors.

The junction temperature (TJ, in °C) is calculated from the ambient

temperature (TA, in °C) and power dissipation (PD, in Watts) according to

the formula:

TJ = TA + (PD • θJA),

where θJA = 43°C/W is the package thermal impedance.

Note 3: This IC includes overtemperature protection that is intended

to protect the device during momentary overload conditions. Junction

temperatures will exceed 150°C when overtemperature protection is

active. Continuous operation above the specified maximum operating

junction temperature may result in device degradation or failure.

SUPPLY VOLTAGE (V)

OSCILLATOR FREQUENCY (kHz)

400

500

600

15 25

3260 G01

300

200

5 10 20 30 35

100

RT = GND

RT = 200kΩ

RT (kΩ)

200

OSCILLATOR FREQUENCY (kHz)

400

600

100

300

500

1 100 1000 10000

3260 G02

TEMPERATURE (°C)

–50

SHUTDOWN CURRENT (µA)

150

3260 G03

0050 100

–25 25 75 125

VIN = 32V

VIN = 12V

VIN = 5V

TEMPERATURE (°C)

–50

QUIESCENT CURRENT (µA)

120

150

3260 G04

0050 100

–25 25 75 125

160

100

140 Burst Mode OPERATION

WITH BOTH LDOs ON

POSITIVE LDO ON

Burst Mode OPERATION

WITH NEGATIVE LDO ON

VIN = 12V

SUPPLY VOLTAGE (V)

QUIESCENT CURRENT (mA)

3260 G05

5 10 20

25 30 35

fOSC = 500kHz

fOSC = 200kHz

fOSC = 50kHz

TEMPERATURE (°C)

–50

QUIESCENT CURRENT (mA)

050 75

3260 G06

–25 25 100 125 150

fOSC = 500kHz

fOSC = 200kHz

fOSC = 50kHz

VIN = 12V

LTC3260

3260fa

Typical perForMance characTerisTics

LDO+ GND Pin Current vs ILOAD LDO+ Load Regulation

ADJ+ Pin Voltage vs Temperature

Effective Open-Loop Resistance

vs Supply Voltage

LDO+ Dropout Voltage

vs Temperature

LDO+ Supply Rejection

Effective Open-Loop Resistance

vs Temperature

VOUT Short-Circuit Current

vs Supply Voltage

Voltage Loss (VIN – |VOUT|)

vs Output Current (Constant

Frequency Mode)

(TA = 25°C, CF LY = 1µF, CIN = COUT = CLDO+ = CLDO– = 10µF unless otherwise noted)

SUPPLY VOLTAGE (V)

0 5

VOUT SHORT-CIRCUIT CURRENT (mA)

100

250

10 20 25

3260 G08

200

150

15 30 35

RT = GND

RT = 200kΩ

OUTPUT CURRENT (mA)

0.1

VOLTAGE LOSS (V)

2.0

2.5

3.0

fOSC = 50kHz

fOSC = 200kHz

fOSC = 500kHz

1 10 100

3260 G09

1.5

1.0

0.5

VIN = 12V

TEMPERATURE (°C)

–50

ADJ+ PIN VOLTAGE (V)

1.200

1.212

150

3260 G11

1.188

1.176 050 100

–25 25 75 125

1.224

ILOAD (mA)

0.08

GND PIN CURRENT (mA)

0.10

0.12

0.14

1 10 100

3260 G14

0.06

0.04

0.02

VIN = 12V

SUPPLY VOLTAGE (V)

EFFECTIVE OPEN-LOOP RESISTANCE (Ω)

3260 G10

525

15 3530

fOSC = 200kHz

fOSC = 500kHz

TEMPERATURE (°C)

–50

EFFECTIVE OPEN-LOOP RESISTANCE (Ω)

0 50 100 150

3620 G07

–25 25 75 125

VIN = 32V

VIN = 25V

VIN = 12V

fOSC = 500kHz

TEMPERATURE (°C)

–50

LDO+ DROPOUT VOLTAGE (mV)

400

600

150

3260 G12

200

0050 100

–25 25 75 125

800 VIN = 12V

ILDO+ = 50mA

300

500

100

700

FREQUENCY (kHz)

LDO+ SUPPLY REJECTION (dB)

0.1 10 100 1000

3260 G13

VIN = 6.5V

VLDO+ = 5V

ILDO+ = 50mA

VRIPPLE = 50mVRMS

CLDO+ = 10µF

ILDO+ (mA)

0.1

1.1994

VLDO+ (V)

1.2002

1.2004

1.2006

1 10 100

3260 G15

1.2000

1.1998

1.1996

VIN = 12V

UNITY GAIN

LTC3260

3260fa

Typical perForMance characTerisTics

LDO+ Load Transient

LDO– Load Transient

VOUT Transient (Burst Mode

Operation, MODE = H)

VOUT Transient

(MODE = Low to High)

LDO Rejection of VOUT RippleLDO– Load Regulation

(TA = 25°C, CF LY = 1µF, CIN = COUT = CLDO+ = CLDO– = 10µF unless otherwise noted)

ADJ– Pin Voltage vs Temperature

LDO– Dropout Voltage

vs Temperature LDO– Power Supply Rejection

TEMPERATURE (°C)

–50

ADJ– PIN VOLTAGE (V)

–1.200

–1.188

150

3260 G16

–1.212

–1.224 050 100

–25 25 75 125

–1.176

TEMPERATURE (°C)

–50

LDO– DROPOUT VOLTAGE (mV)

200

300

150

3260 G17

100

0050 100

–25 25 75 125

400 VOUT = –12V

ILDO– = 50mA

150

250

350

FREQUENCY (kHz)

LDO– SUPPLY REJECTION (dB)

0.1 10 100 1000

3260 G18

VOUT = –6.5V

VLDO– = –5V

ILDO– = –50mA

VRIPPLE = 50mVRMS

CLDO– = 10µF

ILDO– (mA)

0.1

–1.2006

VLDO– (V)

–1.1998

–1.1996

–1.1994

1 10 100

3260 G19

–1.2000

–1.2002

–1.2004

VOUT = –12V

UNITY GAIN

1µs/DIV 3260 G20

VLDO+

10mV/DIV

AC-COUPLED

VLDO–

10mV/DIV

AC-COUPLED

VOUT

10mV/DIV

AC-COUPLED

VIN = 15V

VLDO+ = 12V

VLDO– = –12V

fOSC = 500kHz

ILDO+ = 50mA

ILDO– –50mA

VLDO+

10mV/DIV

AC-COUPLED

ILDO+

40µs/DIV 3260 G21

VIN = 12V

VLDO+ = 5V

20mA

2mA

VLDO–

10mV/DIV

AC-COUPLED

ILDO–

40µs/DIV 3260 G22

VIN = 12V

VLDO– = –5V

REFER TO FIGURE 3

–2mA

–20mA

VOUT

500mV/DIV

AC-COUPLED

IOUT–

2ms/DIV 3260 G23

VIN = 12V

fOSC = 500kHz

–5mA

–50mA

VOUT

500mV/DIV

AC-COUPLED

2ms/DIV 3260 G24

VIN = 12V

fOSC = 500kHz

IOUT = –5mA

MODE

LTC3260

3260fa

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. Connect

a capacitor from BYP– to GND to reduce LDO– output

noise. Leave floating if unused.

ADJ– (Pin 4/ Pin 4): Feedback Input for the Negative Low

Dropout Regulator. This pin servos to a fixed voltage of

–1.2V when the control loop is complete.

LDO– (Pin 5/ Pin 5): Negative Low Dropout (LDO–) Linear

Regulator Output. This pin requires a low ESR (equivalent

series resistance) capacitor with at least 2µF capacitance

to ground for stability.

VOUT (Pin 6/ Pin 6): Charge Pump Output Voltage. In

constant frequency mode (MODE = low) this pin is driven

to –VIN. In Burst Mode operation, (MODE = high) this pin

voltage is regulated to –0.94 • VIN using an internal burst

comparator with hysteretic control.

C– (Pin 7/ Pin 7): Flying Capacitor Negative Connection.

C+ (Pin 8/ Pin 10): Flying Capacitor Positive Connection.

NC (Pins 8, 9 MSOP Only): No Connect. These pins are not

connected to the LT C 3260 die. These pins should be left

floating, connected to ground or shorted to adjacent pins.

VIN (Pin 9/ Pin 11): Input Voltage for Both Charge Pump

and Positive Low Dropout (LDO+) Regulator. VIN should

be bypassed with a low impedance ceramic capacitor.

LDO+ (Pin 10/ Pin 12): Positive Low Dropout (LDO+)

Output. This pin requires a low ESR capacitor with at least

2µF capacitance to ground for stability.

EN– (Pin 11/ Pin 13): Logic Input. A logic “high” on the

EN– pin enables the inverting charge pump as well as the

negative LDO regulator.

MODE (Pin 12/ Pin 14): Logic Input. The MODE pin deter-

mines the charge pump operating mode. A logic “high”

on the MODE pin forces the charge pump to operate in

Burst Mode operation regulating VOUT to approximately

–0.94 • VIN with hysteretic control. A logic “low” on the

MODE pin forces the charge pump to operate as an open-

loop inverter with a constant switching frequency. The

switching frequency in both modes is determined by an

external resistor from the RT pin to GND. In Burst Mode

operation, this represents the frequency of the burst cycles

before the part enters the low quiescent current sleep state.

ADJ+ (Pin 13/ Pin 15): Feedback Input for the Positive

Low Dropout (LDO+) Regulator. This pin servos to a fixed

voltage of 1.2V when the control loop is complete.

BYP+ (Pin 14/Pin 16): LDO+ Reference Bypass Pin. Con-

nect a capacitor from BYP+ to GND to reduce LDO+ output

noise. Leave floating if unused.

GND (Exposed Pad Pin 15/ Exposed Pad Pin 17): Ground.

The exposed package pad is ground and must be soldered

to the PC board ground plane for proper functionality and

for rated thermal performance.

LTC3260

3260fa

block DiagraM

Note: Pin numbers are as per DFN package. Refer to the Pin Functions section for corresponding MSOP pin numbers.

9 10

–

1.2V

REF

INVERTING

CHARGE PUMP

–1.2V

REF

CHARGE

PUMP

AND

INPUT

LOGIC

50kHz

500kHz

OSC

LDO+

EN+

VIN

C+

ADJ+

BYP+

BYP–

ADJ–

LDO–

GND

C–S2

EN–

MODE

VOUT

operaTion

(Refer to the Block Diagram)

The LTC3260 is a high voltage low noise dual output

regulator. It includes an inverting charge pump and two

LDO regulators to generate bipolar low noise supply rails

from a single positive input. It supports a wide input power

supply range from 4.5V to 32V.

Shutdown Mode

In shutdown mode, all circuitry except the internal bias is

turned off. The LTC3260 is in shutdown when a logic low

is applied to both the enable inputs (EN+ and EN–). The

LTC3260 only draws 2µA (typical) from the VIN supply

in shutdown.

Charge Pump Constant Frequency Operation

The LTC3260 provides low noise constant frequency op-

eration when a logic low is applied to the MODE pin. The

charge pump and oscillator circuit are enabled using the

EN– pin. At the beginning of a clock cycle, switches S1 and

S2 are closed. The external flying capacitor across the C+

and C– pins is charged to the VIN supply. In the second

phase of the clock cycle, switches S1 and S2 are opened,

while switches S3 and S4 are closed. In this configuration

the C+ side of the flying capacitor is grounded and charge

is delivered through the C– pin to VOUT. In steady state

the VOUT pin regulates at –VIN less any voltage drop due

to the load current on VOUT or LDO.

LTC3260

3260fa

operaTion

(Refer to the Block Diagram)

Figure 1. Oscillator Frequency vs RT

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.

RT (kΩ)

200

OSCILLATOR FREQUENCY (kHz)

400

600

100

300

500

1 100 1000 10000

3260 F01

Charge Pump Burst Mode Operation

The LTC3260 provides low power Burst Mode operation

when a logic high is applied to the MODE pin. In Burst

Mode operation, the charge pump charges the VOUT pin to

–0.94 • VIN (typical). The part then shuts down the internal

oscillator to reduce switching losses and goes into a low

current state. This state is referred to as the sleep state in

which the IC consumes only about 100µA with both LDOs

enabled. When the output voltage droops enough to over-

come the burst comparator hysteresis, the part wakes up

and commences charge pump cycles until output voltage

exceeds –0.94 • VIN (typical). This mode provides lower

operating current at the cost of higher output ripple and

is ideal for light load operation.

The frequency of charging cycles is set by the external

resistor on the RT pin. The charge pump has a lower

ROL at higher frequencies. For Burst Mode operation it is

recommended that the RT pin be tied to GND. This mini-

mizes the charge pump ROL, quickly charges the output

up to the burst threshold and optimizes the duration of

the low current sleep state.

Charge Pump Soft-Start

The LTC3260 has built in soft-start circuitry to prevent

excessive current flow during start-up. The soft-start is

achieved by internal circuitry that slowly ramps the amount

of current available at the output storage capacitor. The

soft-start circuitry is reset in the event of a commanded

shutdown or thermal shutdown.

Charge Pump Short-Circuit/Thermal Protection

The LTC3260 has built-in short-circuit current limit as

well as overtemperature protection. During a short-circuit

condition, the part automatically limits its output current

to approximately 160mA. If the junction temperature

exceeds approximately 175°C the thermal shutdown

circuitry disables current delivery to the output. Once

the junction temperature drops back to approximately

165°C current delivery to the output is resumed. When

thermal protection is active the junction temperature is

beyond the specified operating range. Thermal protection

is intended for momentary overload conditions outside

normal operation. Continuous operation above the speci-

fied maximum operating junction temperature may impair

device reliability.

Positive Low Dropout Linear Regulator (LDO+)

The positive low dropout regulator (LDO+) supports a load

of up to 50mA. The LDO+ takes power from the VIN pin

and drives the LDO+ output pin to a voltage programmed

by the resistor divider connected between the LDO+, ADJ+

and GND pins. For stability, the LDO+ output must be by-

passed to ground with a low ESR ceramic capacitor that

maintains a capacitance of at least 2µF across operating

temperature and voltage.

The LDO+ is enabled or disabled via the EN+ logic input pin.

When the LDO+ is enabled, a soft-start circuit ramps its

regulation point from zero to the final value over a period

of 75µs, reducing the inrush current on VIN.

LTC3260

3260fa

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:

VLDO+=1.2V •R1

R2 +1











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.

negative by the charge pump circuitry. Soft-start circuitry

in the charge pump also provides soft-start functionality

for the LDO– and prevents excessive inrush currents.

Figure 3 shows the LDO– regulator application circuit.

The LDO– output voltage VLDO– can be programmed by

choosing suitable values of R1 and R2 such that:

VLDO–=–1.2V •R1

R2 +1











When the inverting charge pump is in Burst Mode opera-

tion (MODE = high), the typical hysteresis on the VOUT

pin is 2% of VIN voltage. The LDO– voltage should be set

high enough above VOUT in order to prevent LDO– from

entering dropout during normal operation.

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.

In order to improve transient response, an optional

capacitor, CADJ–, may be used as shown in Figure 3. A

recommended value for CADJ– is 10pF. Experimentation

with capacitor values between 2pF and 22pF may yield

improved transient response.

Figure 2: Positive LDO Application Circuit

VIN

LDO+

EN+

ADJ+

GND

BYP+

CBYP+

COUT

LTC3260

LDO

OUTPUT

3260 F02

1.2V

REF

Figure 3: Negative LDO Application Circuit

VOUT

LDO–

EN–

ADJ–

GND

BYP–CBYP–

CADJ–

COUT

3260 F03

LTC3260

LDO

OUTPUT

–1.2V

REF

Negative Low Dropout Linear Regulator (LDO–)

The negative low dropout regulator (LDO–) supports a

load of up to 50mA. The LDO– takes power from the VOUT

pin (output of the inverting charge pump) and drives the

LDO– output pin to a voltage programmed by the resis-

tor divider connected between the LDO–, ADJ– and GND

pins. For stability, the LDO– output must be bypassed to

ground with a low ESR ceramic capacitor that maintains a

capacitance of at least 2µF across operating temperature

and voltage.

The LDO– is enabled or disabled via the EN– logic input

pin. Initially, when the EN– logic input is low, the charge

pump circuitry is disabled and the VOUT pin is at GND.

When EN– is switched high, the VOUT pin will be driven

LTC3260

3260fa

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 (CF LY ), the nonoverlap

time, the internal switch resistances (RS) and the ESR of

the external capacitors.

Typical ROL values as a function of temperature are shown

in Figure 4

minimum turn-on time. The peak-to-peak output ripple at

the VOUT pin is approximately given by the expression:

VRIPPLE(P-P) ≈IOUT

COUT

fOSC

– tON











where COUT is the value of the output capacitor, fOSC is the

oscillator frequency and tON is the on-time of the oscillator

(1µs typical).

Just as the value of COUT controls the amount of output

ripple, the value of CIN controls the amount of ripple present

at the input (VIN) pin. The amount of bypass capacitance

required at the input depends on the source impedance

driving VIN. For best results it is recommended that VIN

be bypassed with at least 2µF of low ESR capacitance. A

high ESR capacitor such as tantalum or aluminum will

have higher input noise than a low ESR ceramic capacitor.

Therefore, a ceramic capacitor is recommended as the

main bypass capacitance with a tantalum or aluminum

capacitor used in parallel if desired.

Flying Capacitor Selection

The flying capacitor controls the strength of the charge

pump. A 1µF or greater ceramic capacitor is suggested

for the flying capacitor for applications requiring the full

rated output current of the charge pump.

For very light load applications, the flying capacitor may

be reduced to save space or cost. For example, a 0.2µF

capacitor might be sufficient for load currents up to 20mA.

A smaller flying capacitor leads to a larger effective open-

loop resistance (ROL) and thus limits the maximum load

current that can be delivered by the charge pump.

Ceramic Capacitors

Ceramic capacitors of different materials lose their capaci-

tance with higher temperature and voltage at different rates.

For example, a capacitor made of X5R or X7R material

will retain most of its capacitance from –40°C to 85°C

whereas a Z5U or Y5V style capacitor will lose considerable

capacitance over that range. Z5U and Y5V capacitors may

Figure 4. Typical ROL vs Temperature

Input/Output Capacitor Selection

The style and value of capacitors used with the LTC3260

determine several important parameters such as regulator

control loop stability, output ripple, charge pump strength

and minimum turn-on time. To reduce noise and ripple,

it is recommended that low ESR ceramic capacitors be

used for the charge pump and LDO outputs. All capacitors

should retain at least 2µF of capacitance over operating

temperature and bias voltage. Tantalum and aluminum

capacitors can be used in parallel with a ceramic capacitor

to increase the total capacitance but should not be used

alone because of their high ESR. In constant frequency

mode, the value of COUT directly controls the amount of

output ripple for a given load current. Increasing the size of

COUT will reduce the output ripple at the expense of higher

TEMPERATURE (°C)

–50

EFFECTIVE OPEN-LOOP RESISTANCE (Ω)

0 50 100 150

3620 F04

–25 25 75 125

VIN = 32V

VIN = 25V

VIN = 12V

fOSC = 500kHz

LTC3260

3260fa

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.

Table 1 is a list of ceramic capacitor manufacturers and

their websites.

Table 1

AVX www.avxcorp.com

Kemet www.kemet.com

Murata www.murata.com

Taiyo Yuden www.t-yuden.com

Vishay www.vishay.com

TDK www.component.tdk.com

Layout Considerations

Due to high switching frequency and high transient currents

produced by LTC3260, careful board layout is necessary

for optimum performance. A true ground plane and short

connections to all the external capacitors will improve

performance and ensure proper regulation under all condi-

tions. Figure 5 shows an example layout for the LTC3260.

The flying capacitor nodes C+ and C– switch large cur-

rents at a high frequency. These nodes should not be

routed close to sensitive pins such as the LDO feedback

pins (ADJ+ and ADJ–) and internal reference bypass pins

(BYP+ and BYP–).

Thermal Management

At high input voltages and maximum output current, there

can be substantial power dissipation in the LTC3260. If

the junction temperature increases above approximately

175°C, the thermal shutdown circuitry will automatically

deactivate the output. To reduce the maximum junction

temperature, a good thermal connection to the PC board

ground plane is recommended. Connecting the exposed pad

of the package to a ground plane under the device on two

layers of the PC board can reduce the thermal resistance

of the package and PC board considerably.

Derating Power at High Temperatures

To prevent an overtemperature condition in high power

applications, Figure 6 should be used to determine the

maximum combination of ambient temperature and power

dissipation.

The power dissipated in the LTC3260 should always fall

under the line shown for a given ambient temperature. The

power dissipated in the LTC3260 has three components.

Power dissipated in the positive LDO:

PLDO+ = (VIN – VLDO+) • ILDO+

Power dissipated in the negative LDO:

PLDO– = (|VOUT| – |VLDO–|) • ILDO– and

Power dissipated in the inverting charge pump:

PCP = (VIN – |VOUT|) • (IOUT + ILDO–)

where IOUT denotes any additional current that might be

pulled directly from the VOUT pin. The LDO– current is

also supplied by the charge pump through VOUT and is

therefore included in the charge pump power dissipation.

The total power dissipation of the LTC3260 is given by:

PD = PLDO+ + PLDO– + PCP

Figure 5. Recommended Layout

VOUT

VIN

LDO–

LDO+

GND

3260 F05

CBYP+

CF LY

GND

CBYP–

LTC3260

3260fa

applicaTions inForMaTion

The derating curve in Figure 6 assumes a maximum ther-

mal 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.

It is recommended that the LTC3260 be operated in the

region corresponding to TJ ≤ 150°C for continuous op-

eration as shown in Figure 6. Operation beyond 150°C

should be avoided as it may degrade part performance

and lifetime. At high temperatures, typically around 175°C,

the part is placed in thermal shutdown and all outputs are

disabled. When the part cools back down to a low enough

temperature, typically around 165°C, the outputs are re-

enabled and the part resumes normal operation.

Figure 6. Maximum Power Dissipation vs Ambient Temperature

Typical applicaTions

Low Power ±24V Power Supply from a Single-Ended 28V Input Supply

4.7µF

1µF

4.7µF

1.91M

100k

24V

–24V

3260 TA02

LDO+

28V

LDO–

ADJ+

LTC3260

ADJ–

GND

BYP+

BYP–

VIN

VOUT

EN+

C–

MODE

EN–

C+

High Voltage Input to Bipolar Output with Highly Efficient Dividing/Inverting Charge Pump

4.7µF

50V

4.7µF

25V

4.7µF

0.01µF

1µF

50V

1µF

50V

NOTE: THE LTC3260 WILL ALWAYS RUN

IN CONTINUOUS FREQUENCY REGARDLESS

OF THE MODE PIN SETTING BECAUSE VOUT

IS ALWAYS LESS THAN –1/2VIN

MBR0540

14 17 2

316k

100k

316k

–5V

3260 TA04

LDO+

11 12

13.5V TO 32V

LDO–

VOUT

ADJ+

LTC3260

GND RTMODE

ADJ–

BYP+

BYP–

VIN

EN+

C–

EN–

C+

VOUT ~ – VIN – VF– IOUT •ROL

2– VF











AMBIENT TEMPERATURE (°C)

–50

MAXIMUM POWER DISSIPATION (W)

050 75 175

3260 F06

–25 25 100 125 150

RECOMMENDED

OPERATION

TJ = 150°C

θJA = 43°C/W

LTC3260

3260fa

Typical applicaTions

28V Dual Tracking Bipolar Supply with Outputs from ±5V to ±25V

4.7µF

50V

4.7µF

35V

4.7µF

50V

4.7µF

35V

0.01µF

1µF

50V

732k

73.2k

500k

732k

OUT

–OUT

3260 TA05

LDO+

11 12

28V

LDO–

VOUT

ADJ+

LTC3260

GND

MODE

ADJ–

BYP+

BYP–

VIN

EN+

C–

EN–

C+

0.01µF

LTC3260

3260fa

package DescripTion

Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.

3.00 ±0.10

(2 SIDES)

4.00 ±0.10

(2 SIDES)

NOTE:

1. DRAWING PROPOSED TO BE MADE VARIATION OF VERSION (WGED-3) IN JEDEC

PACKAGE OUTLINE MO-229

2. DRAWING NOT TO SCALE

3. ALL DIMENSIONS ARE IN MILLIMETERS

4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE

MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE

5. EXPOSED PAD SHALL BE SOLDER PLATED

6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE

TOP AND BOTTOM OF PACKAGE

0.40 ±0.10

BOTTOM VIEW—EXPOSED PAD

1.70 ±0.10

0.75 ±0.05

R = 0.115

TYP

R = 0.05

TYP

3.00 REF

148

PIN 1

TOP MARK

(SEE NOTE 6)

0.200 REF

0.00 – 0.05

(DE14) DFN 0806 REV B

PIN 1 NOTCH

R = 0.20 OR

0.35 × 45°

CHAMFER

0.25 ±0.05

0.50 BSC

3.30 ±0.10

1.70 ±0.05

3.00 REF

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED

2.20 ±0.05

0.70 ±0.05

3.60 ±0.05

PACKAGE

OUTLINE

0.25 ±0.05

3.30 ±0.05

0.50 BSC

DE Package

14-Lead Plastic DFN (4mm × 3mm)

(Reference LTC DWG # 05-08-1708 Rev B)

LTC3260

3260fa

package DescripTion

Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.

MSOP (MSE16) 0911 REV E

0.53 ±0.152

(.021 ±.006)

SEATING

PLANE

0.18

(.007)

1.10

(.043)

MAX

0.17 –0.27

(.007 – .011)

TYP

0.86

(.034)

REF

0.50

(.0197)

BSC

16151413121110

12345678

NOTE:

1. DIMENSIONS IN MILLIMETER/(INCH)

2. DRAWING NOT TO SCALE

3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.

MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE

4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.

INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE

5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX

6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD SHALL

NOT EXCEED 0.254mm (.010") PER SIDE.

0.254

(.010) 0° – 6° TYP

DETAIL “A”

GAUGE PLANE

5.23

(.206)

MIN

3.20 – 3.45

(.126 – .136)

0.889 ±0.127

(.035 ±.005)

RECOMMENDED SOLDER PAD LAYOUT

0.305 ±0.038

(.0120 ±.0015)

TYP

0.50

(.0197)

BSC

BOTTOM VIEW OF

EXPOSED PAD OPTION

2.845 ±0.102

(.112 ±.004)

2.845 ±0.102

(.112 ±.004)

4.039 ±0.102

(.159 ±.004)

(NOTE 3)

1.651 ±0.102

(.065 ±.004)

1.651 ±0.102

(.065 ±.004)

0.1016 ±0.0508

(.004 ±.002)

3.00 ±0.102

(.118 ±.004)

(NOTE 4)

0.280 ±0.076

(.011 ±.003)

REF

4.90 ±0.152

(.193 ±.006)

DETAIL “B”

CORNER TAIL IS PART OF

THE LEADFRAME FEATURE.

FOR REFERENCE ONLY

NO MEASUREMENT PURPOSE

0.12 REF

0.35

REF

MSE Package

16-Lead Plastic MSOP, Exposed Die Pad

(Reference LTC DWG # 05-08-1667 Rev E)

LTC3260

3260fa

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

revision hisTory

REV DATE DESCRIPTION PAGE NUMBER

A 09/12 Changed Operating Junction Temperature.

Add H- and MP-grade options.

Add Junction to heading of Electrical Characteristics table.

Add H- and MP-grade into Note 2.

Modified Shutdown Current vs Temperature curve for operation to 150°C.

Modified Quiescent Current vs Temperature curve for operation to 150°C.

Corrected Figure 5 Pinout RT and CBYP.

Removed Thermal Shutdown curve from Figure 6.

Clarified 150°C Operation in Derating Power section.

Updated Related Parts list.

Throughout

12, 13

LTC3260

3260fa

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com

 LINEAR TECHNOLOGY CORPORATION 2012

LT 0912 REV A • PRINTED IN USA

relaTeD parTs

Typical applicaTion

Low Noise ±12V Power Supply from a Single-Ended 15V Input Supply (Frequency = 200kHz)

10µF

10nF

10µF

1µF

10µF

909k

200k

909k

100k

12V

–12V

3260 TA03

LDO+

15V

LDO–

ADJ+

LTC3260

ADJ–

GND

BYP+

BYP–

VIN

VOUT

EN+

C–

MODE

EN–

C+

PART NUMBER DESCRIPTION COMMENTS

LTC1144 Switched-Capacitor Wide Input Range Voltage Converter with

Shutdown

Wide Input Voltage Range: 2V to 18V, ISD < 8µA,

SO8 Package

LTC1514/LTC1515 Step-Up/Step-Down Switched-Capacitor DC/DC Converters VIN: 2V to 10V, VOUT: 3.3V to 5V, IQ = 60µA, SO8 Package

1611 150mA Output, 1.4MHz Micropower Inverting Switching Regulator VIN: 0.9V to 10V, VOUT = ±34V, ThinSOT™ Package

LT1614 250mA Output, 600kHz Micropower Inverting Switching Regulator VIN: 0.9V to 6V, VOUT = ±30V, IQ = 1mA, MS8, SO8

Packages

LTC1911 250mA, 1.5MHz Inductorless Step-Down DC/DC Converter VIN: 2.7V to 5.5V, VOUT = 1.5V/1.8V, IQ = 180µA,

MS8 Package

LTC3250/LTC3250-1.2/

LTC3250-1.5

Inductorless Step-Down DC/DC Converters VIN: 3.1V to 5.5V, VOUT = 1.2V, 1.5V, IQ = 35µA,

ThinSOT Package

LTC3251 500mA Spread Spectrum Inductorless Step-Down DC/DC

Converter

VIN: 2.7V to 5.5V, VOUT: 0.9V to 1.6V, 1.2V, 1.5V, IQ = 9µA,

MS10E Package

LTC3252 Dual 250mA, Spread Spectrum Inductorless Step-Down DC/DC

Converter

VIN: 2.7V to 5.5V, VOUT: 0.9V to 1.6V, IQ = 50µA,

DFN12 Package

LT1054/LT1054L Switched-Capacitor Voltage Converters with Regulator VIN: 3.5V to 15V/7V, IOUT = 100mA/125mA, N8, S08,

SO16 Packages

LTC3261 High Voltage, Low Quiescent Current Inverting Charge Pump VIN: 4.5V to 32V, VOUT = –VIN, IOUT = 100mA, MSOP-12

Package