Datasheet

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LTC1574

LTC1574-3.3/LTC1574-5

High Efficiency Step-Down

DC/DC Converters

with Internal Schottky Diode

The LTC

1574 is a family of easy-to-use current mode

DC/DC converters ideally suited for 9V to 5V, 5V to 3.3V

and inverting operation. With an internal 0.9Ω switch (at

a supply voltage of 12V) and a low forward drop Schottky

diode (0.450V typ at 200mA, T

= 25°C), the LTC1574

requires only three external components to construct a

complete high efficiency DC/DC converter.

Under no load condition, the LTC1574 draws only 130µA.

In shutdown, it draws a mere 2µA making this converter

ideal for battery-powered applications. In dropout, the

internal P-channel MOSFET switch is turned on continu-

ously allowing the user to maximize the life of the battery

source.

The maximum inductor current of the LTC1574 family is

pin selectable to either 340mA or 600mA, optimizing

efficiency for a wide range of applications. Operation up to

200kHz permits the use of small surface mount inductors

and capacitors.

For applications requiring higher output current or ultra-

high efficiency, see the LTC1148 or LTC1265 data sheets.

For detailed applications information, see the LTC1174

data sheet.

High Efficiency Step-Down Converter

LTC1574-5 Efficiency

■

Inverting Converters

■

Step-Down Converters

■

Memory Backup Supply

■

Portable Instruments

■

Battery-Powered Equipment

■

Distributed Power Systems

■

High Efficiency: Up to 94%

■

Usable in Noise-Sensitive Products

■

Peak Inductor Current Independent of Inductor Value

■

Short-Circuit Protection

■

Internal Low Forward Drop Schottky Diode

■

Only Three External Components Required

■

Wide V

Range: 4V to 18.5V (Absolute Maximum)

■

Low Dropout Operation

■

Low-Battery Detector

■

Pin Selectable Current Limit

■

Internal 0.9Ω Power Switch: V

< 11V

■

Standby Current: 130µA

■

Active Low Micropower Shutdown

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

and LTC are registered trademarks and LT is a trademark of Linear Technology Corporation.

100µH

†

22µF*

35V

100µF*

10V

1574 TA01

175mA

2, 4, 13, 15

3, 14

5.5V to

16V

GND

LTC1574-5

OUT

PGM

SHDN

OUT

* AVX TPSD226K035

** AVX TPSD107K010

†

COILTRONICS CTX100-4

LOAD CURRENT (mA)

EFFICIENCY (%)

100

10 100

1574 TA02

200

= 6V

= 9V

L = 100µH

OUT

= 5V

PGM

= 0V

Summary of content (8 pages)

PAGE 1
LTC1574 LTC1574-3.3/LTC1574-5 High Efficiency Step-Down DC/DC Converters with Internal Schottky Diode U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO High Efficiency: Up to 94% Usable in Noise-Sensitive Products Peak Inductor Current Independent of Inductor Value Short-Circuit Protection Internal Low Forward Drop Schottky Diode Only Three External Components Required Wide VIN Range: 4V to 18.5V (Absolute Maximum) Low Dropout Operation Low-Battery Detector Pin Selectable Current Limit Internal 0.
PAGE 2
LTC1574 LTC1574-3.3/LTC1574-5 W W W AXI U U U W PACKAGE/ORDER I FOR ATIO U ABSOLUTE RATI GS (Note 1) (Voltage Referred to GND Pin) Input Supply Voltage (Pin 5) ................. – 0.3V to 18.5V Switch Current (Pin 3, 14) ........................................ 1A Switch Voltage (Pin 3, 14) .......................... VIN – 18.5V Operating Temperature Range .................... 0°C to 70°C Junction Temperature (Note 2) ............................ 125°C Storage Temperature Range .................
PAGE 3
LTC1574 LTC1574-3.3/LTC1574-5 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 9V, SHDN = VIN, IPGM = 0V, unless otherwise specified. SYMBOL PARAMETER CONDITIONS MIN IIH SHDN Pin Input Current SHDN = 16V IIL SHDN Pin Input Current 0 ≤ SHDN ≤ 0.8V VF Schottky Diode Forward Voltage Forward Current = 200mA IR Schottky Reverse Current Reverse Voltage = 5V Reverse Voltage = 18.
PAGE 4
LTC1574 LTC1574-3.3/LTC1574-5 U U U PI FU CTIO S NC (Pins 1, 8, 9, 16): No Connection. GND (Pins 2, 4, 13, 15): Ground. SW (Pins 3, 14): Drain of P-Channel MOSFET Switch and Cathode of Schottky Diode. VOUT or VFB (Pin 10): For the LTC1574, this pin connects to the main voltage comparator input. On the LTC1574-5 and LTC1574-3.3, this pin goes to an internal resistive divider which sets the output voltage. VIN (Pin 5): Input Supply Voltage. It must be decoupled close to ground (Pin 4).
PAGE 5
LTC1574 LTC1574-3.3/LTC1574-5 U W U U APPLICATIO S I FOR ATIO going into Pin 12 being negligible, the following expression is used for setting the trip limit:  R4  VLBTRIP = 1.251 +   R3  VIN LTC1574 R4 12 difference between the absolute maximum voltage rating and the output voltage. A maximum of 12V is specified in Figure 4, giving the circuit 1.5V of headroom for VIN. Note that the circuit can operate from a minimum of 4V, making it ideal for a four NiCd cell application.
PAGE 6
LTC1574 LTC1574-3.3/LTC1574-5 U W U U APPLICATIO S I FOR ATIO inductor L1 is chosen for its excellent self-shielding properties. Open magnetic structures such as drum and rod cores are to be avoided since they inject high flux levels into their surroundings. This can become a major source of noise in any converter circuit.
PAGE 7
LTC1574 LTC1574-3.3/LTC1574-5 U W U U APPLICATIO S I FOR ATIO on no-load supply current. Schottky diodes such as MBR0530, BAS85 and BAT84 work well. Another more serious effect of the protection diode leakage is that at no load with nothing to provide a sink for this leakage current, the output voltage can potentially float above the maximum allowable tolerance.
PAGE 8
LTC1574 LTC1574-3.3/LTC1574-5 U TYPICAL APPLICATIO S Low Dropout 5V Step-Down Regulator with Low-Battery Detection High Efficiency 3.3V Regulator VIN 5.5V to 12.5V VIN 4V TO 12.5V 5 4.7k VIN *LOWBATTERY INDICATOR 6 11 162k 0.1µF 12 SHDN IPGM LTC1574-5 LBOUT VOUT LBIN SW 7 3, 14 L1 100µH† + 2, 4, 13, 15 VIN 6 12 11 47µF** 16V ×2 7 SHDN LTC1574-3.3 10 LBIN VOUT IPGM LBOUT SW 3, 14 22µF* 25V ×2 0.1µF VOUT 3.