Datasheet

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LTC1147-3.3

LTC1147-5/LTC1147L

sn1147 1147fds

High Efficiency Step-Down

Switching Regulator Controllers

Figure 1. High Efficiency Step-Down Converter

ITY

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

0V = NORMAL

>1.5V = SHUTDOWN

P-CHANNEL

Si4431DY

1µF

50µH

SENSE

0.05Ω

OUT

5V/2A

100µF

(5.2V TO 14V)

470pF

3300pF

OUT

390µF

MBRD330

LT1147 • F01

GND

PDRIVE

LTC1147-5

SHDN

SENSE

–

1000pF

COILTRONICS CTX50-2-MP

KRL SL-1-C1-0R050J

LOAD CURRENT (A)

0.001

EFFICIENCY (%)

100

0.01 0.1 1

LT1147 • TA01

= 6V

= 10V

LTC1147-5 Efficiency

■

Very High Efficiency: Over 95% Possible

■

Wide V

Range: 3.5V* to 16V

■

Current Mode Operation for Excellent Line and Load

Transient Response

■

High Efficiency Maintained Over Three Decades of

Output Current

■

Low 160µA Standby Current at Light Loads

■

Logic Controlled Micropower Shutdown: I

< 20µA

■

Short-Circuit Protection

■

Very Low Dropout Operation: 100% Duty Cycle

■

High Efficiency in a Small Amount of Board Space

■

Output Can Be Externally Held High in Shutdown

■

Available in 8-Pin SO Package

The LTC

1147 series are step-down switching regulator

controllers featuring automatic Burst Mode

operation to

maintain high efficiencies at low output currents. These

devices drive an external P-channel power MOSFET at

switching frequencies exceeding 400kHz using a constant

off-time current mode architecture providing constant

ripple current in the inductor.

The operating current level is user-programmable via an

external current sense resistor. Wide input supply range

allows operation from 3.5V* to 14V (16V maximum).

Constant off-time architecture provides low dropout regu-

lation limited by only the R

DS(ON)

of the external MOSFET

and resistance of the inductor and current sense resistor.

The LTC1147 series incorporates automatic power saving

Burst Mode

operation to reduce switching losses when

load currents drop below the level required for continuous

operation. Standby power is reduced to only 2mW at

= 10V (at I

OUT

= 0). Load currents in Burst Mode

operation are typically 0mA to 300mA.

For applications where even higher efficiency is required,

refer to the LTC1148 data sheet and Application Note 54.

Burst Mode

is a trademark of Linear Technology Corporation.

*LTC1147L and LTC1147L-3.3 only.

FEATURES

DESCRIPTIO

APPLICATIO S

■

Notebook and Palmtop Computers

■

Portable Instruments

■

Battery-Operated Digital Devices

■

Cellular Telephones

■

DC Power Distribution Systems

■

GPS Systems

Summary of content (16 pages)

PAGE 1
LTC1147-3.3 LTC1147-5/LTC1147L High Efficiency Step-Down Switching Regulator Controllers U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Very High Efficiency: Over 95% Possible Wide VIN Range: 3.
PAGE 2
LTC1147-3.3 LTC1147-5/LTC1147L U W W W ABSOLUTE AXI U RATI GS Input Supply Voltage (Pin 1) .................... 16V to – 0.3V Continuous Output Current (Pin 8) ...................... 50mA Sense Voltages (Pins 4, 5) VIN ≥ 12.7V ...........................................13V to – 0.3V VIN < 12.7V ............................... (VIN + 0.3V) to – 0.3V Operating Ambient Temperature Range LTC1147C ............................................... 0°C to 70°C LTC1147I ........................................
PAGE 3
LTC1147-3.3 LTC1147-5/LTC1147L ELECTRICAL CHARACTERISTICS SYMBOL PARAMETER V5 – V 4 Current Sense Threshold Voltage (Note 6) LTC1147-3.3, LTC1147L-3.3 LTC1147–5 LTC1147L V6 SHDN Pin Threshold LTC1147-3.3/LTC1147-5/LTC1147L-3.3 I6 SHDN Pin Input Current LTC1147-3.3/LTC1147-5/LTC1147L-3.3 TA = 25°C, VIN = 10V, VSHDN = 0V, unless otherwise noted.
PAGE 4
LTC1147-3.3 LTC1147-5/LTC1147L U W TYPICAL PERFOR A CE CHARACTERISTICS Efficiency vs Input Voltage Line Regulation 100 FIGURE 1 CIRCUIT 98 Load Regulation 40 20 FIGURE 1 CIRCUIT ILOAD = 1A 30 20 ILOAD = 1A 92 90 88 ILOAD = 100mA 86 –20 10 ∆VOUT (mV) 94 ∆VOUT (mV) EFFICIENCY (%) 96 0 –10 –40 VIN = 12V –60 –80 –30 82 80 –40 4 0 16 12 8 INPUT VOLTAGE (V) –100 0 8 4 12 20 1.6 VSHUTDOWN = 2V (NOT AVAILABLE ON LTC1147L) 18 VOUT = 5V 1.4 1.2 0.9 0.
PAGE 5
LTC1147-3.3 LTC1147-5/LTC1147L U U U PI FU CTIO S VIN (Pin 1): Main Supply Pin. Must be closely decoupled to ground Pin 7. CT (Pin 2): External capacitor CT from Pin 2 to ground sets the operating frequency. The actual frequency is also dependent upon the input voltage. ITH (Pin 3): Gain Amplifier Decoupling Point. The current comparator threshold increases with the Pin 3 voltage. SENSE – (Pin 4): Connects to internal resistive divider which sets the output voltage.
PAGE 6
LTC1147-3.3 LTC1147-5/LTC1147L U OPERATIO (Refer to Functional Diagram) The LTC1147 series uses a current mode, constant offtime architecture to switch an external P-channel power MOSFET. Operating frequency is set by an external capacitor at CT (Pin 2). The output voltage is sensed by an internal voltage divider connected to SENSE– (Pin 4). A voltage comparator V, and a gain block G, compare the divided output voltage with a reference voltage of 1.25V.
PAGE 7
LTC1147-3.3 LTC1147-5/LTC1147L U W U U APPLICATIO S I FOR ATIO The basic LTC1147 application circuit is shown in Figure 1. External component selection is driven by the load requirement and begins with the selection of RSENSE. Once RSENSE is known, CT and L can be chosen. Next, the power MOSFET and D1 are selected. Finally, CIN and COUT are selected and the loop is compensated. The circuit shown in Figure 1 can be configured for operation up to an input voltage of 16V.
PAGE 8
LTC1147-3.3 LTC1147-5/LTC1147L U U W U APPLICATIO S I FOR ATIO 1000 VSENSE – = VOUT = 5V CAPACITANCE (pF) 800 Inductor Core Selection 600 400 VIN = 12V 200 VIN = 7V VIN = 10V 0 0 200 100 FREQUENCY (kHz) 300 LTC1147 • F03 Figure 3. Timing Capacitor Value is given by: f≈ 1 tOFF series will delay entering Burst Mode operation and efficiency will be degraded at low currents. ) 1– VOUT VIN ) where: ) ) V tOFF = (1.3)(104)(CT) REG VOUT VREG is the desired output voltage (i.e., 5V, 3.
PAGE 9
LTC1147-3.3 LTC1147-5/LTC1147L U W U U APPLICATIO S I FOR ATIO used. For VIN > 8V, a standard threshold MOSFET (VGS(TH) < 4V) may be used. If VIN is expected to drop below 8V, a logic-level threshold MOSFET (VGS(TH) < 2.5V) is strongly recommended. When a logic-level MOSFET is used, the LTC1147 supply voltage must be less than the absolute maximum VGS ratings for the MOSFET. The maximum output current IMAX determines the RDS(ON) requirement for the power MOSFET.
PAGE 10
LTC1147-3.3 LTC1147-5/LTC1147L U W U U APPLICATIO S I FOR ATIO Optimum efficiency is obtained by making the ESR equal to RSENSE. As the ESR is increased up to 2RSENSE, the efficiency degrades by less than 1%. If the ESR is greater than 2RSENSE, the voltage ripple on the output capacitor will prematurely trigger Burst Mode operation, resulting in disruption of continuous mode and an efficiency hit which can be several percent.
PAGE 11
LTC1147-3.3 LTC1147-5/LTC1147L U W U U APPLICATIO S I FOR ATIO Although all dissipative elements in the circuit produce losses, four main sources usually account for most of the losses in LTC1147 circuits: 1) LTC1147 DC bias current, 2) MOSFET gate charge current, 3) I2R losses, and 4) voltage drop of the Schottky diode. 1. The DC supply current is the current which flows into VIN (Pin 1) less the gate charge current.
PAGE 12
LTC1147-3.3 LTC1147-5/LTC1147L U W U U APPLICATIO S I FOR ATIO Other losses including CIN and COUT ESR dissipative losses, MOSFET switching losses, and inductor core losses, generally account for less than 2% total additional loss. fMIN = Design Example PP = As a design example, assume VIN = 5V (nominal), VOUT = 3.3V, IMAX = 1A, and f = 130kHz; RSENSE, CT and L can immediately be calculated: RSENSE = 100mV/1A = 0.1Ω tOFF = (1/130kHz)[1 – (3.3/5)] = 2.61µs CT = 2.61µs/(1.3)(104) = 220pF L = (5.
PAGE 13
LTC1147-3.3 LTC1147-5/LTC1147L U U W U APPLICATIO S I FOR ATIO Board Layout Checklist When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the LTC1147 series. These items are also illustrated graphically in the layout diagram of Figure 7. Check the following in your layout: 1. Are the signal and power grounds segregated? The LTC1147 ground (Pin 7) must return separately to a) the power and b) signal grounds.
PAGE 14
LTC1147-3.3 LTC1147-5/LTC1147L U TYPICAL APPLICATIO S 3.3V Low Dropout High Efficiency Regulator VIN 3.5V TO 12V + CIN 47µF 16V Si9433DY D1 MBRS130LT3 0.1µF L* 10µH LTC1147L-3.3 1 2 3 CT 120pF CC 3300pF 4 RC 1k PDRIVE VIN CT GND ITH SHDN SENSE – SENSE + 8 7 6 SHUTDOWN 5 + RSENSE** 0.068Ω 0.01µF COUT 100µF 10V AVX VOUT 3.3V/1.25A *SUMIDA CDR74B-100LC **IRC LRC-LR2010-01-R068-F LTC1147 • F08 Precision Constant Current Source VIN 10V TO 14V + Si3455DV D1 MBRS130LT3 0.
PAGE 15
LTC1147-3.3 LTC1147-5/LTC1147L U TYPICAL APPLICATIO S 2.5V/2A Regulator VIN 3.5V TO 12V + Si9433DY CIN 15µF 25V × 2 D1 MBRD330 0.1µF L* 10µH LTC1147L 1 2 3 CT 120pF CC 3300pF 4 RC 1k PDRIVE VIN 8 7 CT GND ITH SHDN (VFB) 6 SENSE + 5 SENSE – R1 49.9k 1% I00pF RSENSE** 0.05Ω 0.01µF R2 49.9k 1% + COUT 220µF 10V × 2 AVX 2.5V/2A *COILTRONICS CTX10-4 **IRC LR2512-01-0R050-G U PACKAGE DESCRIPTIO LTC1147 • F11 Dimensions in inches (millimeters) unless otherwise noted.
PAGE 16
LTC1147-3.3 LTC1147-5/LTC1147L U TYPICAL APPLICATION 3.3V/2A Output High Efficiency Regulator VIN 4V TO 14V + Si4431DY 0.1µF 1 2 3 CT 220pF CC 3300pF 4 RC 1k PDRIVE VIN GND LTC1147-3.3 SHDN ITH CT SENSE + SENSE – L* D1 20µH MBRS130LT3 8 7 6 SHUTDOWN COUT 220µF 10V AVX 5 + 0.01µF RSENSE** 0.05Ω *COILTRONICS CTX20-4 **KRL SP-1/2-A1-OR050 LTC1147 • F12 U PACKAGE DESCRIPTIO CIN 22µF 25V × 2 VOUT 3.3V/2A Dimensions in inches (millimeters) unless otherwise noted.