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LTC1928-5

, LTC and LT are registered trademarks of Linear Technology Corporation

ThinSOT is a trademark of Linear Technology Corporation.

FEATURES

APPLICATIO S

DESCRIPTIO

TYPICAL APPLICATION

■

Low Output Noise: 90

RMS

(100kHz BW)

■

Fixed Output Voltage: 5V

■

Input Voltage Range: 2.7V to 4.4V

■

No Inductors Required

■

Uses Small Ceramic Capacitors

■

Output Current Up to 30mA

■

550kHz Switching Frequency

■

Low Operating Current: 190µA

■

Low Shutdown Current: 4µA

■

Internal Thermal Shutdown and Current Limiting

■

Low Profile (1mm) ThinSOT

Package

The LTC

1928-5 is a doubler charge pump with an internal

low noise, low dropout (LDO) linear regulator. The part is

designed to provide a low noise boosted supply voltage for

powering noise sensitive devices such as high frequency

VCOs in wireless applications.

An internal charge pump converts a 2.7V to 4.4V input to

a boosted output, while the internal LDO regulator con-

verts the boosted voltage to a low noise regulated output.

The regulator is capable of supplying up to 30mA of output

current. Shutdown reduces the supply current to <8µA,

removes the load from V

by disabling the regulator and

discharges V

OUT

to ground through a 200Ω switch.

The LTC1928-5 LDO regulator is stable with only 2µF on

the output. Small ceramic capacitors can be used, reduc-

ing PC board area.

The LTC1928-5 is short-circuit and overtemperature pro-

tected. The part is available in a 6-pin low profile

(1mm)ThinSOT package.

■

VCO Power Supplies for Cellular Phones

■

2-Way Pagers

■

Wireless PCMCIA Cards

■

Portable Medical Instruments

■

Low Power Data Acquisition

■

Remote Transmitters

■

White LED Drivers

■

GaAs Switches

Figure 1. Low Noise 5V Power Supply

Doubler Charge Pump with

Low Noise Linear Regulator

in ThinSOT

Output Noise (BW = 10Hz to 2.5MHz)

OUT

200µV/DIV

CPO

= C

OUT

= 4.7µF 100µs/DIV 19285 TA01

OUT

= 10mA

= 3V

OUT

= 5V

= 25°C

OUT

CPO

GND

2.7V TO 4.4V

CN/SHDN

4.7µF

0.47µF

4.7µF

19285 F01

OUT

LTC1928-5

Summary of content (8 pages)

PAGE 1
LTC1928-5 Doubler Charge Pump with Low Noise Linear Regulator in ThinSOT U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO Low Output Noise: 90µVRMS (100kHz BW) Fixed Output Voltage: 5V Input Voltage Range: 2.7V to 4.
PAGE 2
LTC1928-5 W W W AXI U U ABSOLUTE RATI GS U U W PACKAGE/ORDER I FOR ATIO (Note 1) VIN to Ground ..............................................– 0.3V to 5V VOUT Voltage ...........................................– 0.3V to 5.25V CPO to Ground ........................................................ 10V CN/SHDN to Ground ..................... – 0.3V to (VIN + 0.3V) VOUT Short-Circuit Duration ............................. Indefinite IOUT .................................................................
PAGE 3
LTC1928-5 ELECTRICAL CHARACTERISTICS Note 4: Operating conditions are limited by maximum junction temperature. The regulated output specification will not apply for all possible combinations of input voltage and output current. When operating at maximum input voltage, the output current range may be limited. When operating at maximum output current, the input voltage range may be limited. Note 5: CN/SHDN must be driven with a source impedance of at least 100Ω (RSOURCE) to prevent damage to the part.
PAGE 4
LTC1928-5 U W TYPICAL PERFOR A CE CHARACTERISTICS Operating Current vs VIN (No Load) 260 Efficiency vs Supply Voltage 100 TA = 25°C TA = 25°C IOUT = 15mA CFLY = 0.47µF 90 180 160 OUTPUT VOLTAGE (V) 200 80 70 60 140 4.989 4.988 4.987 4.986 4.985 4.984 50 120 100 2.5 TA = 25°C VIN = 3V CFLY = 0.47µF 4.900 220 EFFICIENCY (%) OPERATING CURRENT (µA) 240 Output Voltage vs Output Current 4.901 4.983 4.982 40 3.0 3.5 VIN (V) 4.0 0 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.
PAGE 5
LTC1928-5 U U U PIN FUNCTIONS VIN (Pin 1): Input Voltage, 2.7V to 4.4V. VIN should be bypassed with a ≥ 2µF low ESR capacitor as close to the pin as possible for best performance. A minimum capacitance value of 0.1µF is required. GND (Pin 2): System Ground. VOUT (Pin 3): Low Noise Regulated Output Voltage. VOUT should be bypassed with a ≥ 2µF low ESR capacitor as close to the pin as possible for best performance. The VOUT voltage is internally set to 5V. CPO (Pin 4): Boosted Unregulated Voltage.
PAGE 6
LTC1928-5 W U U VCPO U RCPO APPLICATIONS INFORMATION RDROPOUT + + 2V IN – – VOUT VDROPOUT CCPO IOUT 19285 F02 Figure 2. Equivalent Circuit External CPO Loading The CPO output can drive an external load (for example, an LDO). The current required by this additional load will reduce the available current from VOUT. If the external load requires 1mA, the available current at VOUT will be reduced by 1mA. Short-Circuit and Thermal Protection VOUT can be shorted to ground indefinitely.
PAGE 7
LTC1928-5 U U W U APPLICATIONS INFORMATION Power-On Reset General Layout Considerations Upon initial power-up, a power-on reset circuit ensures that the internal functions are correctly initialized. Once VIN reaches about 1V, the power-on reset circuit will enable the part as long as the CN/SHDN pin is not pulled low. Due to the high switching frequency and high transient currents produced by the device, careful board layout is a must.
PAGE 8
LTC1928-5 U U W U APPLICATIONS INFORMATION VIN 2.7V TO 4.4V CIN 4.7µF LTC1928-5 1 5 CFLY 0.47µF 6 VIN VOUT CP CPO CN/SHDN GND 3 VRIPPLE < 800µVP-P 4 2 CCPO 4.7µF 19285 F05 100Ω 2N7002 5V COUT 4.7µF SHDN Figure 5. Low Noise 5V Supply with Shutdown U PACKAGE DESCRIPTION S6 Package 6-Lead Plastic SOT-23 SOT-23 (Original) SOT-23 (ThinSOT) A .90 – 1.45 (.035 – .057) 1.00 MAX (.039 MAX) A1 .00 – 0.15 (.00 – .006) .01 – .10 (.0004 – .004) A2 .90 – 1.30 (.035 – .051) .80 – .90 (.