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LTC1149

LTC1149-3.3/LTC1149-5

ESCRIPTIO

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Operation to 48V Input Voltage

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Ultrahigh Efficiency: Up to 95%

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Current Mode Operation for Excellent Line and

Load Transient Response

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High Efficiency Maintained over Wide Current Range

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Logic-Controlled Micropower Shutdown

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Short-Circuit Protection

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Very Low Dropout Operation: 100% Duty Cycle

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Synchronous FET Switching for High Efficiency

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Adaptive Nonoverlap Gate Drives

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Available in 16-Pin Narrow SO Package

The LTC

1149 series is a family of synchronous step-

down switching regulator controllers featuring automatic

Burst Mode

operation to maintain high efficiencies at

low output currents. These devices drive external comple-

mentary power MOSFETs at switching frequencies up

to 250kHz using a constant off-time current-mode archi-

tecture.

Special onboard regulation and level-shift circuitry allow

operation at input voltages from dropout to 48V (60V

absolute max). The constant off-time architecture main-

tains constant ripple current in the inductor, easing the

design of wide input range converters. Current mode

operation provides excellent line and load transient

response. The operating current level is user-program-

mable via an external current sense resistor.

The LTC1149 series incorporates automatic power saving

Burst Mode

operation when load currents drop below the

level required for continuous operation. Standby power is

reduced to only about 8mW at V

= 12V. In shutdown,

both MOSFETs are turned off.

High Efficiency Synchronous

Step-Down Switching Regulators

Figure 1. High Efficiency Step-Down Regulator

ITY

0.068µF

CAP

PDRIVE

LTC1149-5

SHDN1

SGND

PGATE

SHDN2

SENSE

–

SENSE

P, RGNDS

NGATE

1000pF

N-CHANNEL

IRFR024

0.047µF

1N4148

P-CHANNEL

IRFR9024

D1

1N5819

L*

62µH

SENSE



0.05Ω

OUT



5V/2A

OUT



220µF



100µF

100V

3.3µF

0V = NORMAL

>2V = SHUTDOWN

3300µF



470pF

1149 F01

*COILTRONICS CTX62-2-MP

**KRL SL-1-C1-0R050J

LOAD CURRENT (A)

0.02

EFFICIENCY (%)

100

0.2 2

1149 TA01

= 12V

= 24V

FIGURE 1 CIRCUIT

LTC1149-5 Efficiency

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Notebook and Palmtop Computers

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Portable Instruments

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Battery-Operated Digital Devices

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Industrial Power Distribution

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Avionics Systems

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Telecom Power Supplies

, 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
LTC1149 LTC1149-3.3/LTC1149-5 High Efficiency Synchronous Step-Down Switching Regulators U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ The LTC ®1149 series is a family of synchronous stepdown switching regulator controllers featuring automatic Burst ModeTM operation to maintain high efficiencies at low output currents. These devices drive external complementary power MOSFETs at switching frequencies up to 250kHz using a constant off-time current-mode architecture.
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LTC1149 LTC1149-3.3/LTC1149-5 U W W W Input Supply Voltage (Pin 2)...................... – 15V to 60V VCC Output Current (Pin 3) .................................. 50mA VCC Input Voltage (Pin 5)........................................ 16V Continuous Output Current (Pins 4, 13) .............. 50mA Sense Voltages (Pins 8, 9) VIN ≥ 12.7V .......................................... 13V to – 0.3V VIN < 12.7V ............................. (VCC + 0.3V) to – 0.3V Shutdown Voltages (Pins 10, 15) ..................
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LTC1149 LTC1149-3.3/LTC1149-5 ELECTRICAL CHARACTERISTICS SYMBOL PARAMETER V 9 – V8 Current Sense Threshold Voltage LTC1149 LTC1149-3.3 LTC1149-5 V10 TA = 25°C, VIN = 12V, V10 = 0V (Note 2), unless otherwise noted. CONDITIONS MIN TYP MAX UNITS V8 = 5V, V10 = 1.32V (Forced) V8 = VOUT – 100mV ● 130 25 150 170 mV mV V8 = 3.5V (Forced) V8 = VOUT – 100mV ● 130 25 150 170 mV mV V8 = 5.3V (Forced) V8 = VOUT – 100mV ● 130 25 150 170 mV mV 0.5 0.8 2 0.8 1.
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LTC1149 LTC1149-3.3/LTC1149-5 U W TYPICAL PERFOR A CE CHARACTERISTICS Line Regulation Efficiency vs Input Voltage 100 Load Regulation 20 60 FIGURE 1 CIRCUIT ILOAD = 1A FIGURE 1 CIRCUIT ILOAD = 1A 40 FIGURE 1 CIRCUIT VIN = 24V 0 –20 90 ∆VOUT (mV) 20 ∆VOUT (mV) EFFICIENCY (%) 95 0 –40 –20 –60 –40 –80 85 80 0 10 30 20 INPUT VOLTAGE (V) 40 –100 –60 50 0 10 20 30 INPUT VOLTAGE (V) 1149 G01 0 50 40 0.
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LTC1149 LTC1149-3.3/LTC1149-5 U U U PI FU CTIO S PGATE (Pin 1): Level-Shifted Gate Drive Signal for Top P-Channel MOSFET. The voltage swing at Pin 1 is from VIN to VIN – VCC. VIN (Pin 2): Main Supply Input Pin. VCC (Pin 3): Output Pin of Low Dropout 10V Regulator. Pin 3 is not protected against DC short circuits. PDRIVE (Pin 4): High Current Gate Drive for Top P-Channel MOSFET. The voltage swing at Pin 4 is from VCC to ground. VCC (Pin 5): Regulated 10V Input for Driver and Control Supplies.
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LTC1149 LTC1149-3.3/LTC1149-5 U OPERATIO (Refer to Functional Diagram) current is made proportional to the output voltage (measured by Pin 8) to model the inductor current, which decays at a rate which is also proportional to the output voltage. While the timing capacitor is discharging, the NGATE output is high, turning on the N-channel MOSFET. When the voltage on the timing capacitor has discharged past VTH1, comparator T trips, setting the flip-flop.
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LTC1149 LTC1149-3.3/LTC1149-5 TEST CIRCUIT + 0.1µF + IRF9Z34 VIN 0.068µF 220µF 100V MBR380 1 2 0.047µF 3 4 + 1µF 5 6 7 390pF 3300pF 8 + 1k PGATE CAP VIN SHDN2 VCC RGND PDRIVE NGATE LTC1149 VCC PGND CT SGND ITH SENSE – 16 + IRFZ34 V15 15 14 13 50µH 12 11 + VFB / 10 SHDN1 9 SENSE + V10 25k + V8 V9 – V8 75k + 220µF 0.05Ω 1000pF VOUT 1149 TC U U W U APPLICATIO S I FOR ATIO Typical Application Circuit The basic LTC1149 series application circuit is shown in Figure 1.
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LTC1149 LTC1149-3.3/LTC1149-5 U U W U APPLICATIO S I FOR ATIO The LTC1149 series automatically extends tOFF during a short circuit to allow sufficient time for the inductor current to decay between switch cycles. The resulting ripple current causes the average short-circuit current ISC(AVG) to be reduced to approximately IMAX. 0.18 0.14 1– VOUT VIN ) where: 0.12 0.10 ) ) VREG VOUT Note that as VIN decreases, the frequency decreases. When the input to output voltage differential drops below 1.
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LTC1149 LTC1149-3.3/LTC1149-5 U U W U APPLICATIO S I FOR ATIO Inductor Core Selection Once the minimum value for L is known, the type of inductor must be selected. High efficiency converters generally cannot afford the core loss found in low cost powdered iron cores, forcing the use of more expensive ferrite, molypermalloy, or Kool Mµ® cores. Actual core loss is independent of core size for a fixed inductor value, but it is very dependent on inductance selected. As inductance increases, core losses go down.
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LTC1149 LTC1149-3.3/LTC1149-5 U U W U APPLICATIO S I FOR ATIO the N-channel MOSFET operating in continuous mode are given by: V –V N-Ch Duty Cycle = IN OUT VIN V –V N-Ch PD = IN OUT (IMAX)2 (1 + ∂N)RDS(ON) VIN where ∂ is the temperature dependency of RDS(ON). Note that there is no transition loss term in the N-channel dissipation equation because the drain-to-source voltage is always low when the N-channel MOSFET is turning on or off.
PAGE 11
LTC1149 LTC1149-3.3/LTC1149-5 U U W U APPLICATIO S I FOR ATIO output ripple at low frequencies will be large enough to trip the voltage comparator. This causes the Burst Mode operation to be activated when the LTC1149 series would normally be in continuous operation. The effect is most pronounced with low values of RSENSE and can be improved by operating at higher frequencies with lower values of L. The output remains in regulation at all times.
PAGE 12
LTC1149 LTC1149-3.3/LTC1149-5 U U W U APPLICATIO S I FOR ATIO the ground side of the output to prevent the absolute maximum voltage ratings of the sense pins from being exceeded. This is shown in Figure 5. When the current sense comparator is operating at 0V common mode, the off-time increases approximately 40%, requiring the use of a smaller timing capacitor CT. Efficiency Considerations The percent efficiency of a switching regulator is equal to the output power divided by the input power times 100%.
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LTC1149 LTC1149-3.3/LTC1149-5 U U W U APPLICATIO S I FOR ATIO LTC1149 Package Dissipation High input voltage applications in which large MOSFETs are being driven at high frequencies may cause the maximum junction temperature rating for the LTC1149 series to be exceeded. The LTC1149 supply current is dominated by the gate charge supply current, which is given as a function of operating frequency in the Typical Performance Characteristics.
PAGE 14
LTC1149 LTC1149-3.3/LTC1149-5 U U W U APPLICATIO S I FOR ATIO 25mV minimum current comparator threshold. This technique is also useful for eliminating audible noise from certain types of inductors in high current (IOUT > 5A) applications when they are lightly loaded. An external offset is put in series with the SENSE – pin to subtract from the built-in 25mV offset. An example of this technique is shown in Figure 6. Two 100Ω resistors are inserted in series with the leads from the sense resistor.
PAGE 15
LTC1149 LTC1149-3.3/LTC1149-5 U U W U APPLICATIO S I FOR ATIO + BOLD LINES INDICATE HIGH CURRENT PATHS 1N4148 CIN + 1N4148 P-CHANNEL VIN 0.068µF D1 1µF + 1 2 3 0.047µF 4 5 6 7 CT 3300pF 8 N-CHANNEL PGATE CAP VIN SD2 VCC PDRIVE RGND NGATE VCC PGND CT SGND ITH VFB/ SHDN1 SENSE – SENSE + – 16 15 SHUTDOWN 14 L 13 12 11 10 – 100pF R1 + 9 COUT R2 1k VOUT RSENSE + 1000pF OUTPUT DIVIDER REQUIRED WITH ADJUSTABLE VERSION ONLY 1149 F08 Figure 8.
PAGE 16
LTC1149 LTC1149-3.3/LTC1149-5 U TYPICAL APPLICATIO S VIN 8V TO 20V 1N4148 + 1N4148 IRFR9024 1 0.068µF 0.047µF 2 3 4 5 6 7 + 1µF 390pF 3300pF 8 PGATE CAP VIN SHDN2 VCC R-GND L* 68µH 16 ITH SHDN1 SENSE – SENSE + VOUT 3.3V/1A 14 + IRFR024 P-DRIVE NGATE LTC1149-3.3 12 VCC PGND SGND RSENSE** 0.1Ω 15 13 CT 100µF 35V 1N5818 220µF 6.3V AVX 11 10 0V = NORMAL >2V = SHUTDOWN 9 1k 1000pF 1149 F10 *COILTRONICS CTX02-11932 **DALE WSC-1/2-0.1 Figure 10.
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LTC1149 LTC1149-3.3/LTC1149-5 U TYPICAL APPLICATIO S VIN 5.5V TO 25V 1N4148 + 1N4148 Si9435DY 1 0.068µF 0.047µF 2 3 4 5 6 7 + 1µF 220pF 3300pF 8 PGATE CAP VIN SHDN2 VCC RGND L* 33µH 16 ITH SHDN1 SENSE – SENSE + VOUT 5V/2A 14 + Si9410DY PDRIVE NGATE LTC1149-5 12 VCC PGND S-GND RSENSE** 0.05Ω 15 13 CT 220µF 35V 1N5818 220µF 10V × 2 AVX 11 10 SHUTDOWN 9 1k 1000pF 1149 F12 *COILTRONICS CTX33-4 Kool Mµ **KRL SL-1-C1-0R050J Figure 12. Ultra Wide Input Range (5.
PAGE 18
LTC1149 LTC1149-3.3/LTC1149-5 U TYPICAL APPLICATIO S VIN 48V 1N4148 + 1N4148 MTD2955 1 0.068µF 2 0.047µF 3 4 5 6 7 + 3.3µF 620pF 3300pF 8 PGATE CAP VIN SHDN2 VCC RGND L* 68µH 16 ITH SHDN1 VOUT 5V/2.5A + IRFZ34 MBR380 220µF 10V OS-CON 11 10 SHUTDOWN 100Ω 9 SENSE + SENSE – RSENSE** 0.04Ω 14 PDRIVE NGATE LTC1149-5 12 VCC PGND SGND 0.1µF 15 13 CT 100µF 100V 1k 1000pF 100Ω 1149 F14 *HURRICANE LAB HL-KI168M **IRC LR2512-01-R040-G Figure 14. High Efficiency 48V Input 5V/2.
PAGE 19
LTC1149 LTC1149-3.3/LTC1149-5 U TYPICAL APPLICATIO S VIN 12V TO 36V 1N4148 + 1000µF 63V 220Ω 10k 2N3906 VN2222LL 0.1µF 470Ω 2N2222 1 2 3 0.1µF PGATE VIN CAP SHDM2 VCC RGND 16 15 MUR110 13 PDRIVE NGATE LTC1149-5 5 12 VCC PGND 7 + 3.3µF 820pF 3300pF 8 CT SGND ITH SHDN1 SENSE – SENSE + RSENSE** 0.
PAGE 20
LTC1149 LTC1149-3.3/LTC1149-5 U PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. S Package 16-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.386 – 0.394* (9.804 – 10.008) 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) 16 0.004 – 0.010 (0.101 – 0.254) 15 13 14 12 11 10 9 0° – 8° TYP 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 0.050 (1.270) TYP 0.014 – 0.019 (0.355 – 0.483) 0.