Datasheet

ManualsBrandsLINEAR TECHNOLOGY ManualsPMICsPMIC - DC/DC voltage regulator Converter, Converter/amplifier, SEPIC MSOP 8

LTC1474/LTC1475

Low Quiescent Current

High Efficiency Step-Down

Converters

LOAD CURRENT (mA)

EFFICIENCY (%)

100

0.03 3 300

1474/75 TA01

0.3 30

= 5V

= 10V

= 15V

L = 100µH

OUT

= 3.3V

SENSE

= 0Ω

LTC1474 Efficiency

Figure 1. High Efficiency Step-Down Converter

GND

SENSE

LBI

RUN

LBO

LTC1474-3.3

100k

LOW BATTERY IN

RUN SHDN

0.1µF

10µF

25V

4V TO 18V

LOW BATTERY OUT

1474/75 F01

100µH

MBR0530

100µF

6.3V

OUT

3.3V AT 250mA

L1 = SUMIDA CDRH74-101

FEATURES

DESCRIPTION

■

High Efficiency: Over 92% Possible

■

Very Low Standby Current: 10

A Typ

■

Available in Space Saving 8-Lead MSOP Package

■

Internal 1.4Ω Power Switch (V

= 10V)

■

Wide V

Range: 3V to 18V Operation

■

Very Low Dropout Operation: 100% Duty Cycle

■

Low-Battery Detector Functional During Shutdown

■

Programmable Current Limit with Optional

Current Sense Resistor (10mA to 400mA Typ)

■

Short-Circuit Protection

■

Few External Components Required

■

Active Low Micropower Shutdown: I

= 6µA Typ

■

Pushbutton On/Off (LTC1475 Only)

■

3.3V, 5V and Adjustable Output Versions

The LTC

1474/LTC1475 series are high efficiency step-

down converters with internal P-channel MOSFET power

switches that draw only 10µA typical DC supply current at

no load while maintaining output voltage. The LTC1474

uses logic-controlled shutdown while the LTC1475 fea-

tures pushbutton on/off.

The low supply current coupled with Burst Mode

opera-

tion enables the LTC1474/LTC1475 to maintain high effi-

ciency over a wide range of loads. These features, along

with their capability of 100% duty cycle for low dropout

and wide input supply range, make the LTC1474/LTC1475

ideal for moderate current (up to 300mA) battery-powered

applications.

The peak switch current is user-programmable with an

optional sense resistor (defaults to 325mA minimum if not

used) providing a simple means for optimizing the design

for lower current applications. The peak current control

also provides short-circuit protection and excellent start-

up behavior. A low-battery detector that remains functional

in shutdown is provided .

The LTC1474/LTC1475 series availability in 8-lead MSOP

and SO packages and need for few additional components

provide for a minimum area solution.

APPLICATIONS

■

Cellular Telephones and Wireless Modems

■

4mA to 20mA Current Loop Step-Down Converter

■

Portable Instruments

■

Battery-Operated Digital Devices

■

Battery Chargers

■

Inverting Converters

■

Intrinsic Safety Applications

TYPICAL APPLICATION

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

Burst Mode is a trademark of Linear Technology Corporation.

Summary of content (20 pages)

PAGE 1
LTC1474/LTC1475 Low Quiescent Current High Efficiency Step-Down Converters DESCRIPTION U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ The LT C®1474/LTC1475 series are high efficiency stepdown converters with internal P-channel MOSFET power switches that draw only 10µA typical DC supply current at no load while maintaining output voltage. The LTC1474 uses logic-controlled shutdown while the LTC1475 features pushbutton on/off.
PAGE 2
LTC1474/LTC1475 W W U W ABSOLUTE MAXIMUM RATINGS Input Supply Voltage (VIN).........................– 0.3V to 20V Switch Current (SW, SENSE) .............................. 750mA Switch Voltage (SW) ............. (VIN – 20V) to (VIN + 0.3V) VFB (Adjustable Versions) ..........................– 0.3V to 12V VOUT (Fixed Versions) ................................ –0.3V to 20V LBI, LBO ....................................................– 0.3V to 20V RUN, SENSE .................................. – 0.
PAGE 3
LTC1474/LTC1475 ELECTRICAL CHARACTERISTICS TA = 25°C, VIN = 10V, VRUN = open, RSENSE = 0, unless otherwise noted. SYMBOL PARAMETER CONDITIONS VFB Feedback Voltage LTC1474/LTC1475 ILOAD = 50mA VOUT Regulated Output Voltage LTC1474-3.3/LTC1475-3.3 LTC1474-5/LTC1475-5 ILOAD = 50mA MIN TYP MAX UNITS ● 1.205 1.230 1.255 V ● ● 3.234 4.900 3.300 5.000 3.366 5.
PAGE 4
LTC1474/LTC1475 U W TYPICAL PERFORMANCE CHARACTERISTICS Efficiency vs Input Voltage Line Regulation 40 FIGURE 1 CIRCUIT L: CDRH73-101 90 30 ILOAD = 200mA 85 FIGURE 1 CIRCUIT 30 20 RSENSE = 0Ω 20 ILOAD = 25mA ∆VOUT (mV) EFFICIENCY (%) 95 40 FIGURE 1 CIRCUIT ILOAD = 100mA ∆VOUT (mV) 100 Load Regulation 10 RSENSE = 0.
PAGE 5
LTC1474/LTC1475 U U U PIN FUNCTIONS VOUT/VFB (Pin 1): Feedback of Output Voltage. In the fixed versions, an internal resistive divider divides the output voltage down for comparison to the internal 1.23V reference. In the adjustable versions, this divider must be implemented externally. SW (Pin 5): Drain of Internal PMOS Power Switch. Cathode of Schottky diode must be closely connected to this pin.
PAGE 6
LTC1474/LTC1475 U OPERATIO (Refer to Functional Diagram) The LTC1474/LTC1475 are step-down converters with internal power switches that use Burst Mode operation to keep the output capacitor charged to the proper output voltage while minimizing the quiescent current.
PAGE 7
LTC1474/LTC1475 U W U U APPLICATIONS INFORMATION The basic LTC1474/LTC1475 application circuit is shown in Figure 1, a high efficiency step-down converter. External component selection is driven by the load requirement and begins with the selection of RSENSE. Once RSENSE is known, L can be chosen. Finally D1, CIN and COUT are selected. RSENSE Selection The current sense resistor (RSENSE) allows the user to program the maximum inductor/switch current to optimize the inductor size for the maximum load.
PAGE 8
LTC1474/LTC1475 U W U U APPLICATIONS INFORMATION If the LMIN calculated is not practical, a larger IPEAK should be used. Although the above equation provides the minimum, better performance (efficiency, line/load regulation, noise) is usually gained with higher values. At higher inductances, peak current and frequency decrease (improving efficiency) and inductor ripple current decreases (improving noise and line/load regulation).
PAGE 9
LTC1474/LTC1475 U U W U APPLICATIONS INFORMATION CIN and COUT Selection At higher load currents, when the inductor current is continuous, the source current of the P-channel MOSFET is a square wave of duty cycle VOUT/VIN. To prevent large voltage transients, a low ESR input capacitor sized for the maximum RMS current must be used. The maximum capacitor current is given by: CIN Required IRMS = [ ( IMAX VOUT VIN − VOUT )] 1/ 2 VIN This formula has a maximum at VIN = 2VOUT, where IRMS = IOUT/2.
PAGE 10
LTC1474/LTC1475 U W U U APPLICATIONS INFORMATION small that this loss is negligible at loads above a milliamp but at no load accounts for nearly all of the loss. The second component, the gate charge current, results from switching the gate capacitance of the internal P-channel switch. Each time the gate is switched from high to low to high again, a packet of charge dQ moves from VIN to ground. The resulting dQ/dt is the current out of VIN which is typically much larger than the DC bias current.
PAGE 11
LTC1474/LTC1475 U U W U APPLICATIONS INFORMATION LTC1475 Pushbutton On/Off and Microprocessor Interface The LTC1475 provides pushbutton control of power on/off for use with handheld products. A momentary ground on the ON pin sets an internal S/R latch to run mode while a momentary ground on the LBI/OFF pin resets the latch to shutdown mode. See Figure 6 for a comparsion of on/off operation of the LTC1474 and LTC1475 and Figure 7 for a comparison of the circuit implementations.
PAGE 12
LTC1474/LTC1475 U W U U APPLICATIONS INFORMATION with a built-in internal disconnect. The user needs to assess his/her application to determine whether this situation could occur. If so, additional protection is necessary. where P is the power dissipated by the regulator and θJA is the thermal resistance from the junction of the die to the ambient temperature. Prevention against latchup can be accomplished by simply connecting a Schottky diode across the SW and VIN pins as shown in Figure 8.
PAGE 13
LTC1474/LTC1475 U U W U APPLICATIONS INFORMATION OUTPUT DIVIDER REQUIRED WITH ADJUSTABLE VERSION ONLY 10pF LTC1474 1 VOUT R2 R1 + 2 3 COUT 4 VFB 8 RUN VIN 7 100k L LBO LBI GND SENSE SW 1000pF 6 RSENSE 5 1474/75 F09 0.1µF CIN D1 + VIN BOLD LINES INDICATE HIGH PATH CURRENTS Figure 9. LTC1474/LTC1475 Layout Diagram (See Board Layout Checklist) 5.
PAGE 14
LTC1474/LTC1475 U TYPICAL APPLICATIONS VIN 3.5V TO 18V 10pF + 4.7µF† 35V 1Ω** 1Ω** 2Ω** 1000pF 6 3 * SUMIDA CDRH73-271 ** 3 PARALLEL STANDARD RESISTORS PROVIDE LEAST EXPENSIVE SOLUTION (SEE RSENSE SELECTION SECTION) † AVX TPSC475M035 †† AVX TPSC107M006 RUN 100k 8 0.1µF 7 VIN SENSE LBI RUN VFB LTC1474 LBO GND SW 1.43M 1% 1 1M 1% 2 L* 270µH + 5 VOUT 3V 100mA 100µF†† 6.3V D1 MBR0530 4 1474/75 F10 Figure 10.
PAGE 15
LTC1474/LTC1475 U TYPICAL APPLICATIONS MBR0530 VIN 3.5V TO 6V 10pF + + 0.1µF 22µF** 16V 4.7M 1% 7 6 VIN SENSE 3 RUN VOUT –12V 70mA 22µF†† 25V LBI 100k 8 VFB LTC1474 LBO RUN SW GND 1 536k 1% 2 + 22µF†† 25V + 5 VIN (V) 10µF† L* 200µH 25V 4 * COILTRONICS CTX200-4 ** AVX TPSC226M016 † AVX TPSC106M025 †† AVX TPSD226M025 L* 200µH VOUT 12V 70mA D1 MBR0530 ILOAD(MAX) 3.5 30mA 4 50mA 5 70mA 6 90mA 1474/75 F12 Figure 12. 5V to ±12V Regulator + 0.
PAGE 16
LTC1474/LTC1475 U TYPICAL APPLICATIONS VIN 3.5V TO 12V ON/OFF†† + 0.1µF 10µF** 25V TP0610 7 6 3 8 10M SENSE VIN VOUT LTC1474-5 LBI LBO RUN SW GND 1 2 L* 100µH + 5 33µF 10V D1 MBR0530 4 VIN (V) ILOAD(MAX) 3.5 100mA 5 140mA † 8 190mA 12 240mA VOUT –5V 140mA AT VIN = 5V * SUMIDA CDRH74-101 ** AVX TPSC106M025 † AVX TPSC336M010 †† RUN: ON/OFF = 0, SHUTDOWN: 0N/OFF = V IN Figure 14. Positive-to-Negative (– 5V) Converter VIN 8V TO 18V 10pF + 4.7µF** 35V 0.
PAGE 17
LTC1474/LTC1475 U TYPICAL APPLICATIONS VIN 4V TO 18V + 4.7µF† 35V 0.1µF 2.2M 7 6 3 1M 100k 8 RUN VIN SENSE VOUT LTC1474-3.3 LBI LBO RUN SW GND 1 2 L* 100µH + 100µF†† 6.3V VOUT 3.3V 250mA 5 D1 MBR0530 4 * SUMIDA CDRH73-101 † AVX TPSC475M035 †† AVX TPSC107M006 1474/75 F16 Figure 16. High Efficiency 3.3V Regulator with Low Battery Lockout VIN 5.7V TO 18V + 4.7µF** 35V 0.1µF 7 3.
PAGE 18
LTC1474/LTC1475 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. MS8 Package 8-Lead Plastic MSOP (LTC DWG # 05-08-1660) 0.118 ± 0.004* (3.00 ± 0.102) 8 7 6 5 0.118 ± 0.004** (3.00 ± 0.102) 0.192 ± 0.004 (4.88 ± 0.10) 1 0.040 ± 0.006 (1.02 ± 0.15) 0.007 (0.18) 2 3 4 0.034 ± 0.004 (0.86 ± 0.102) 0° – 6° TYP 0.021 ± 0.006 (0.53 ± 0.015) SEATING PLANE 0.012 (0.30) 0.0256 REF (0.65) TYP 0.006 ± 0.004 (0.15 ± 0.
PAGE 19
LTC1474/LTC1475 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.189 – 0.197* (4.801 – 5.004) 8 7 6 5 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 1 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0.053 – 0.069 (1.346 – 1.752) 0°– 8° TYP 0.016 – 0.050 0.406 – 1.270 0.014 – 0.019 (0.355 – 0.483) 2 3 4 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.
PAGE 20
LTC1474/LTC1475 U TYPICAL APPLICATION 10pF VIN 3.5V to 18V + 0.1µF 4.7µF** 35V 7 1.8M 6 1M 100k MMBT2N2222LT1 8 3 VIN SENSE ON LTC1475 LBI/OFF 1M ON OFF VFB LBO GND SW 1 2 1.02M 1% 1M 1% + L* 100µH VOUT 2.5V 250mA 100µF† 6.3V 5 4 D1 MBR0530 * SUMIDA CDRH73-101 ** AVX TPSC475M035 † AVX TPSC107M006 1474/75 F19 Figure 19.