Datasheet

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LTC1174

LTC1174-3.3/LTC1174-5

1174fe

High Efficiency

Step-Down and Inverting

DC/DC Converter

High Efficiency Step-Down Converter

LTC1174-5 Efficiency

■

High Efficiency: Up to 94%

■

Peak Inductor Current Independent of

Inductor Value

■

Short-Circuit Protection

■

Optimized for 5V to – 5V Applications

■

Wide V

Range: 4V to 18.5V

■

Low Dropout Operation

■

Low-Battery Detector

■

Pin Selectable Current Limit

■

Internal 0.9Ω Power Switch: V

= 9V

■

Only Four External Components Required

■

130µA Standby Current

■

Active Low Micropower Shutdown

■

Distributed Power Systems

■

Step-Down Converters

■

Inverting Converters

■

Memory Backup Supply

■

Portable Instruments

■

Battery-Powered Equipment

The LTC

1174 is a simple current mode DC/DC converter

ideally suited for 9V to 5V, 5V to 3.3V or 5V to –5V

operation. With an internal 0.9Ω switch (at a supply

voltage of 9V), the LTC1174 requires only four external

components to construct a complete high efficiency

DC/DC converter.

Under a no load condition the LTC1174 draws only 130µA.

In shutdown, it draws a mere 1µA making this converter

ideal for current sensitive 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 LTC1174 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 data sheet.

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

LTC1174-5

OUT

PGM

GND

SHUTDOWN

OUT

100µH

†

100µF**

10V

175mA

15µF*

25V

×3

1N5818

1174 TA01

†

(3) AVX TPSD156K025

AVX TPSD107K010

COILTRONICS CTX100-4

LOAD CURRENT (mA)

EFFICIENCY (%)

100

10 100

1174 TA02

200

= 6V

= 9V

L = 100µH

OUT

= 5V

PGM

= 0V

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

All other trademarks are the property of their respective owners.

Summary of content (20 pages)

PAGE 1
LTC1174 LTC1174-3.3/LTC1174-5 High Efficiency Step-Down and Inverting DC/DC Converter U FEATURES DESCRIPTIO ■ The LTC®1174 is a simple current mode DC/DC converter ideally suited for 9V to 5V, 5V to 3.3V or 5V to – 5V operation. With an internal 0.9Ω switch (at a supply voltage of 9V), the LTC1174 requires only four external components to construct a complete high efficiency DC/DC converter.
PAGE 2
LTC1174 LTC1174-3.3/LTC1174-5 W W W AXI U U ABSOLUTE RATI GS (Note 1) (Voltage Referred to GND Pin) Input Supply Voltage (Pin 6) LTC1174 ........................................... – 0.3V to 13.5V LTC1174HV ...................................... – 0.3V to 18.5V Switch Current (Pin 5) .............................................. 1A Switch Voltage (Pin 5) LTC1174 ................................................. VIN – 13.5V LTC1174HV ............................................ VIN – 18.
PAGE 3
LTC1174 LTC1174-3.3/LTC1174-5 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 9V, VSHUTDOWN = VIN, IPGM = 0V, unless otherwise noted.
PAGE 4
LTC1174 LTC1174-3.3/LTC1174-5 ELECTRICAL CHARACTERISTICS Note 3: Guaranteed by design. Note 4: Dynamic supply current is higher due to the gate charge being delivered at the switching frequency. Note 5: Current into Pin 6 only, measured without electrolytic input capacitor. Note 6: The off-time is wafer-sort trimmed.
PAGE 5
LTC1174 LTC1174-3.3/LTC1174-5 U W TYPICAL PERFOR A CE CHARACTERISTICS Switch Leakage Current vs Temperature Line Regulation 6 ILOAD = 100mA IPGM = 0V 95 VIN = 13.
PAGE 6
LTC1174 LTC1174-3.3/LTC1174-5 U U U PI FU CTIO S SW(Pin5): Drain of the P-Channel MOSFET Switch. Cathode of Schottky diode must be closely connected to this pin. VOUT (VFB) (Pin 1): For the LTC1174, this pin connects to the main voltage comparator’s input. On the LTC1174-3.3 and LTC1174-5 this pin goes to an internal resistive divider which sets the output voltage. VIN (Pin 6): Input Supply Voltage. It must be decoupled close to ground Pin 4. LBOUT (Pin 2): Open Drain of an N-Channel Pull-Down.
PAGE 7
LTC1174 LTC1174-3.3/LTC1174-5 U OPERATIO (Refer to Functional Diagram) The LTC1174 uses a constant off-time architecture to switch its internal P-channel power MOSFET. The off-time is set by an internal timing capacitor and the operating frequency is a function of VIN. The output voltage is set by an internal resistive divider (LTC1174-3.3 and LTC1174-5) or an external divider returned to VFB Pin 1 (LTC1174). A voltage comparator A1 compares the divided output voltage to a reference voltage of 1.25V.
PAGE 8
LTC1174 LTC1174-3.3/LTC1174-5 U W U U APPLICATIO S I FOR ATIO Inductor Core Selection With the value of L selected, the type of inductor must be chosen. Basically there are two kinds of losses in an inductor, core and copper Core losses are dependent on the peak-to-peak ripple current and the core material. However it is independent of the physical size of the core. By increasing the inductance the inductor’s peak-to-peak ripple current will decrease, therefore reducing core loss.
PAGE 9
LTC1174 LTC1174-3.3/LTC1174-5 U W U U APPLICATIO S I FOR ATIO Catch Diode Selection The catch diode carries load current during the off-time. The average diode current is therefore dependent on the P-channel switch duty cycle. At high input voltages the diode conducts most of the time. As VIN approaches VOUT the diode conducts only a small fraction of the time. The most stressful condition for the diode is when the output is short-circuited.
PAGE 10
LTC1174 LTC1174-3.3/LTC1174-5 U W U U APPLICATIO S I FOR ATIO VOUT LTC1174 VFB 6.8nF** R2 100pF* R1 1 * ADJUSTABLE APPLICATIONS ** LOW NOISE APPLICATIONS 1174 F04 Figure 4. LTC1174 Adjustable Configuration INPUT VOLTAGE 4V TO 12V 3 2 7 + 6 VIN LBIN 0.1µF SHUTDOWN LBOUT VOUT IPGM SW LTC1174HV-5 GND 4 8 47µF* 16V ×2 1 5 50µH** MBRS140T3 + 47µF* 16V ×2 * AVX TPSD476K016 ** COILTRONICS CTX50-4 VOUT –5V 45mA 1174 F05 Figure 5.
PAGE 11
LTC1174 LTC1174-3.3/LTC1174-5 U W U U APPLICATIO S I FOR ATIO Board Layout Checklist DESIGN EXAMPLE When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the LTC1174. These items are also illustrated graphically in the layout diagram in Figure 7. Check the following in your layout: As a design example, assume VIN = 9V (nominal), VOUT = 5V, and IOUT = 350mA maximum. The LTC1174-5 is used for this application, with IPGM (Pin 7) connected to VIN.
PAGE 12
LTC1174 LTC1174-3.3/LTC1174-5 U W U U APPLICATIO S I FOR ATIO Solving for L in the above equation and with VD = 0.6V, L = 44.8µH. The next higher standard value of L is 50µH (example: Coiltronics CTX50-4). The operating frequency, neglecting voltage across diode VD is: ⎛ V ⎞ f ≈ 2.5 • 105 ⎜1 − OUT ⎟ VIN ⎠ ⎝ = 111kHz With the value of L determined, the requirements for CIN and COUT are calculated.
PAGE 13
LTC1174 LTC1174-3.3/LTC1174-5 U TYPICAL APPLICATIO S 6V to 5V Step-Down Regulator with Low-Battery Detection INPUT VOLTAGE 6V * LOW-BATTERY INDICATOR IS SET TO TRIP AT VIN = 5.5V ** AVX TPSD476K016 D1 = MBRS140T3 (SURFACE MOUNT) 1N5818 † L1 SELECTION MANUFACTURER PART NO. TYPE COILTRONICS CTX100-4 SURFACE MOUNT SUMIDA CD75-101 SURFACE MOUNT GOWANDA GA10-103K THROUGH HOLE 6 VIN 4.7k *LOWBATTERY INDICATOR 162k 7 IPGM 0.1µF SHUTDOWN + 8 47µF** 16V ×2 2 1 LBOUT VOUT LTC1174-5 3 5 SW LBIN GND 47.
PAGE 14
LTC1174 LTC1174-3.3/LTC1174-5 U TYPICAL APPLICATIO S Low Noise 3V Regulator INPUT VOLTAGE 4V TO 12.5V + 6 VIN 7 3 2 IPGM SHUTDOWN LBIN VFB LTC1174 LBOUT SW 22µF* 25V ×3 8 0.1µF 1 6.8nF 50µH† 5 GND + 4 42k 100µF** 10V ×2 1N5818 * AVX TPSD226K025 ** AVX TPSD105K010 † COILTRONICS CTX50-4 VOUT 3V 450mA 30k 1174 TA05 Positive-to-Negative (– 5V) Converter INPUT VOLTAGE 4V TO 12.5V * LOW-BATTERY INDICATOR VIN(V) IOUT MAX(mA) IS SET TO TRIP AT VIN = 4.
PAGE 15
LTC1174 LTC1174-3.3/LTC1174-5 U TYPICAL APPLICATIO S Positive-to-Negative (– 3.3V) Converter INPUT VOLTAGE 4V TO 13.5V * LOW-BATTERY INDICATOR IS SET TO TRIP AT VIN = 4.4V VIN(V) IOUT MAX(mA) ** AVX TPSD336K020 175 4 *** AVX TPSD105K010 205 D1 = MBRS140T3 (SURFACE MOUNT) 5 230 6 1N5818 † 255 7 L1 SELECTION MANUFACTURER COILTRONICS COILCRAFT SUMIDA GOWANDA PART NO. CTX50-3 DT3316-473 CD54-470 GA10-472K TYPE SURFACE MOUNT SURFACE MOUNT SURFACE MOUNT THROUGH HOLE 6 VIN 4.
PAGE 16
LTC1174 LTC1174-3.3/LTC1174-5 U TYPICAL APPLICATIO S 9V to 5V Pre-Post Regulator INPUT VOLTAGE 6V TO 12.5V 3 * SANYO OS-CON ** AVX TPSD476K016 D1 = MBRS140T3 (SURFACE MOUNT) 1N5818 † L1 SELECTION MANUFACTURER COILTRONICS COILCRAFT SUMIDA GOWANDA †† PART NO. CTX50-3 DT3316-473 CD54-470 GA10-472K 2 7 TYPE SURFACE MOUNT SURFACE MOUNT SURFACE MOUNT THROUGH HOLE + 6 VIN LBIN SHUTDOWN LBOUT VFB LTC1174 IPGM SW 100µF* 16V 0.1µF 8 1 8 5 L1† 50µH GND 4 + D1 110k†† 47µF** 16V, ×2 100pF 0.
PAGE 17
LTC1174 LTC1174-3.3/LTC1174-5 U TYPICAL APPLICATIO S 9V to 5V, – 5V Outputs INPUT VOLTAGE 4V TO 12.5V * SANYO OS-CON ** WIMA MKS2 † COILTRONICS CTX100-4 VIN(V) IOUT MAX(mA) 4 75 6 100 8 125 10 145 12 160 13 180 L1B 3 2 CTX100-4 4 + 6 VIN 7 IPGM 0.1µF SHUTDOWN 100µF* 20V 0.1µF 8 1 VOUT LBIN LTC1174HV-5 2 5 LBOUT SW 3 VOUT 5V 135mA AT VIN = 9V 3.
PAGE 18
LTC1174 LTC1174-3.3/LTC1174-5 U TYPICAL APPLICATIO S Automatic Current Selection INPUT VOLTAGE 6V TO 12.5V 6 VIN 100k 100µF* 20V 2 TPO610L + 7 0.1µF 3 LBOUT SHUTDOWN IPGM VOUT LTC1174-5 LBIN SW 8 1 5 50µH† + GND 100k 1N5818 4 100k 100µF* 16V VOUT 5V 0mA TO 320mA 36.
PAGE 19
LTC1174 LTC1174-3.3/LTC1174-5 U PACKAGE DESCRIPTIO N8 Package 8-Lead PDIP (Narrow .300 Inch) (Reference LTC DWG # 05-08-1510) .300 – .325 (7.620 – 8.255) ( 8.255 +0.889 –0.381 .130 ± .005 (3.302 ± 0.127) .045 – .065 (1.143 – 1.651) .065 (1.651) TYP .008 – .015 (0.203 – 0.381) +.035 .325 –.015 .400* (10.160) MAX ) 8 7 6 5 1 2 3 4 .255 ± .015* (6.477 ± 0.381) .120 (3.048) .020 MIN (0.508) MIN .018 ± .003 .100 (2.54) BSC N8 1002 (0.457 ± 0.076) NOTE: 1.
PAGE 20
LTC1174 LTC1174-3.3/LTC1174-5 U TYPICAL APPLICATIO Battery Charger INPUT VOLTAGE 8V TO 12.5V * AVX TAJD226K020 ** AVX TAJD107K010 D1,D2 = MBRS140T3 (SURFACE MOUNT) 1N5818 † L1 SELECTION MANUFACTURER COILTRONICS COILCRAFT SUMIDA GOWANDA PART NO. CTX50-2P DT3316-473 CD54-470 GA10-472K VIN(V) IOUT MAX(mA) 8 320 9 325 10 330 11 335 12 335 TYPE SURFACE MOUNT SURFACE MOUNT SURFACE MOUNT THROUGH HOLE + 6 VIN 7 3 2 0.