Datasheet

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LTC1751/LTC1751-3.3/LTC1751-5

APPLICATIO S

FEATURES

DESCRIPTIO

TYPICAL APPLICATIO

Micropower, Regulated

Charge Pump

DC/DC Converters

■

5V Output Current: 100mA (V

≥ 3V)

■

3.3V Output Current: 80mA (V

≥ 2.5V)

■

Ultralow Power: 20µA Quiescent Current

■

Regulated Output Voltage: 3.3V ±4%, 5V ±4%, ADJ

■

No Inductors

■

Short-Circuit/Thermal Protection

■

Range: 2V to 5.5V

■

800kHz Switching Frequency

■

Very Low Shutdown Current: <2µA

■

Shutdown Disconnects Load from V

■

PowerGood/Undervoltage Output

■

Adjustable Soft-Start Time

■

Available in an 8-Pin MSOP Package

■

Li-Ion Battery Backup Supplies

■

Local 3V and 5V Conversion

■

Smart Card Readers

■

PCMCIA Local 5V Supplies

■

White LED Backlighting

The LTC

1751 family are micropower charge pump DC/

DC converters that produce a regulated output voltage at

up to 100mA. The input voltage range is 2V to 5.5V.

Extremely low operating current (20µA typical with no

load) and low external parts count (one flying capacitor

and two small bypass capacitors at V

and V

OUT

) make

them ideally suited for small, battery-powered applica-

tions.

The LTC1751 family operate as Burst Mode

switched

capacitor voltage doublers to achieve ultralow quiescent

current. They have thermal shutdown capability and can

survive a continuous short circuit from V

OUT

to GND. The

PGOOD pin on the LTC1751-3.3 and LTC1751-5 indicates

when the output voltage has reached its final value and if

the output has an undervoltage fault condition. The FB pin

of the adjustable LTC1751 can be used to program the

desired output voltage or current. An optional soft-start

capacitor may be used at the SS pin to prevent excessive

inrush current during start-up.

The LTC1751 family is available in an 8-pin MSOP

package.

, LTC and LT are registered trademarks of Linear Technology Corporation.

Burst Mode is a trademark of Linear Technology Corporation.

SHDN

GND

OUT

PGOOD

–

LTC1751-5

OUT

5V ±4%

OUT

≤ 100mA, V

≥ 3V

OUT

≤ 50mA, V

≥ 2.7V

2.7V

TO 5.5V

10µF

FLY

1µF

PGOOD

100k

OFF ON

1751 TA01

10µF

FLY

= MURATA GRM39X5R105K6.3AJ

C1, C2 = MURATA GRM40X5R106K6.3AJ

Regulated 5V Output from a 2.7V to 5.5V Input

Output Voltage vs Input Voltage

INPUT VOLTAGE (V)

2.5

4.8

OUTPUT VOLTAGE (V)

4.9

5.0

5.1

5.2

3.0 3.5 4.0 4.5

1751 TA02

5.0 5.5

OUT

= 50mA

FLY

= 1µF

OUT

= 10µF

= 25°C

= –40°C

= 85°C

Summary of content (12 pages)

PAGE 1
LTC1751/LTC1751-3.3/LTC1751-5 Micropower, Regulated Charge Pump DC/DC Converters U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO 5V Output Current: 100mA (VIN ≥ 3V) 3.3V Output Current: 80mA (VIN ≥ 2.5V) Ultralow Power: 20µA Quiescent Current Regulated Output Voltage: 3.3V ±4%, 5V ±4%, ADJ No Inductors Short-Circuit/Thermal Protection VIN Range: 2V to 5.
PAGE 2
LTC1751/LTC1751-3.3/LTC1751-5 W W W AXI U U ABSOLUTE RATI GS U U W PACKAGE/ORDER I FOR ATIO (Note 1) VIN to GND .................................................. – 0.3V to 6V PGOOD, FB, VOUT to GND ........................... – 0.3V to 6V SS, SHDN to GND ........................ – 0.3V to (VIN + 0.3V) VOUT Short-Circuit Duration ............................. Indefinite IOUT (Note 2)....................................................... 125mA Operating Temperature Range (Note 3) ..
PAGE 3
LTC1751/LTC1751-3.3/LTC1751-5 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full specified temperature range, otherwise specifications are at TA = 25°C. CFLY = 1µF, CIN = 10µF, COUT = 10µF unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS LTC1751-3.3/LTC1751-5 UVL PGOOD Undervoltage Low Threshold Relative to Regulated VOUT (Note 6) ● –11 –7 –3 % UVH PGOOD Undervoltage High Threshold Relative to Regulated VOUT (Note 6) ● –8 – 4.
PAGE 4
LTC1751/LTC1751-3.3/LTC1751-5 U W TYPICAL PERFOR A CE CHARACTERISTICS (LTC1751-3.3) Short-Circuit Output Current vs Input Voltage Power Efficiency vs Load Current 100 250 VIN = 2V 70 OUTPUT CURRENT (mA) EFFICIENCY (%) TA = 25°C 90 CFLY = 1µF = 10µF C 80 OUT VIN = 2.75V 60 50 VIN = 3.3V 40 VIN = 4.4V 30 20 TA = 25°C CFLY = 1µF 200 150 100 10 0 0.001 0.01 0.1 1 10 LOAD CURRENT (mA) 50 2.0 100 2.5 3.5 4.0 3.
PAGE 5
LTC1751/LTC1751-3.3/LTC1751-5 U W TYPICAL PERFOR A CE CHARACTERISTICS (LTC1751-5) Short-Circuit Output Current vs Input Voltage Power Efficiency vs Load Current 100 250 VIN = 2.7V 70 OUTPUT CURRENT (mA) EFFICIENCY (%) TA = 25°C 90 CFLY = 1µF COUT = 10µF 80 VIN = 4.1V 60 VIN = 5.5V 50 40 30 20 TA = 25°C CFLY = 1µF 200 150 100 10 0 0.001 0.01 0.1 1 10 LOAD CURRENT (mA) 50 100 2.0 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) 1751 G11 Start-Up 5.0 5.
PAGE 6
LTC1751/LTC1751-3.3/LTC1751-5 W W SI PLIFIED BLOCK DIAGRA S LTC1751-3.
PAGE 7
LTC1751/LTC1751-3.3/LTC1751-5 U W U U APPLICATIO S I FOR ATIO Operation (Refer to Simplified Block Diagrams) The LTC1751 family uses a switched capacitor charge pump to boost VIN to a regulated output voltage. Regulation is achieved by sensing the output voltage through a resistor divider and enabling the charge pump when the divided output drops below the lower trip point of COMP1. When the charge pump is enabled, a 2-phase nonoverlapping clock activates the charge pump switches.
PAGE 8
LTC1751/LTC1751-3.3/LTC1751-5 U W U U APPLICATIO S I FOR ATIO Flying Capacitor Selection Warning: A polarized capacitor such as tantalum or aluminum should never be used for the flying capacitor since its voltage can reverse upon start-up of the LTC1751. Low ESR ceramic capacitors should always be used for the flying capacitor. The flying capacitor controls the strength of the charge pump. In order to achieve the rated output current, it is necessary to have at least 0.
PAGE 9
LTC1751/LTC1751-3.3/LTC1751-5 U W U U APPLICATIO S I FOR ATIO There are several ways to reduce output voltage ripple. For applications requiring VIN to exceed 3.3V or for applications requiring < 100mV of peak-to-peak ripple, a larger COUT capacitor (22µF or greater) is recommended. A larger capacitor will reduce both the low and high frequency ripple due to the lower charging and discharging slew rates as well as the lower ESR typically found with higher value (larger case size) capacitors.
PAGE 10
LTC1751/LTC1751-3.3/LTC1751-5 U W U U APPLICATIO S I FOR ATIO While the LTC1751-3.3/LTC1751-5 versions have internal resistive dividers to program the output voltage, the programmable LTC1751 may be set to an arbitrary voltage via an external resistive divider. Since it employs a voltage doubling charge pump, it is not possible to achieve output voltages greater than twice the available input voltage. Figure 3 shows the required voltage divider connection.
PAGE 11
LTC1751/LTC1751-3.3/LTC1751-5 U TYPICAL APPLICATIO S USB Port to Regulated 5V Power Supply with Soft-Start 2-Cell NiCd or NiMH to 3.3V with Low Standby Current 1µF 1µF 5 1Ω 3 10µF 6 C– C+ VIN VOUT 5 2 2-CELL NiCd OR NiMH 10µF LTC1751-5 7 3 VOUT = 5V 100k SHDN + + 10µF 7 OFF ON 8 1nF 1 SS PGOOD 8 PGOOD GND 6 C– C+ VIN VOUT 2 3.3V 40mA 10µF LTC1751-3.
PAGE 12
LTC1751/LTC1751-3.3/LTC1751-5 U TYPICAL APPLICATIO Current Mode White or Blue LED Driver with PWM Brightness Control C4 1µF 6 3V TO 4.5V Li-Ion BATTERY 3 C1 10µF 17ms VSHDN 7 t 8 5 C+ C– VIN VOUT LTC1751 SHDN SS FB GND UP TO 6 LEDS 2 1 C2 10µF 82Ω 4 82Ω 82Ω 82Ω 82Ω 82Ω 1751 TA03 C3 680pF U PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. MS8 Package 8-Lead Plastic MSOP (LTC DWG # 05-08-1660) 0.043 (1.10) MAX 0.007 (0.18) 0.034 (0.86) REF 0.