Datasheet

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LT1575/LT1577

Ultrafast Transient Response,

Low Dropout Regulators

Adjustable and Fixed

TYPICAL APPLICATION

1

2

3

8

7

6

5



SHDN



GND

OUT

IPOS

INEG

GATE

COMP

C2

1µF

C5

220µF

GND

1575/77 TA01

OUT



3.3V

R2

5Ω

R1

7.5k

12V

LT1575-3.3

C4

1000pF

FOR T > 45°C:

C6 = 24 × 1µF X7R 

CERAMIC SURFACE 

MOUNT CAPACITORS.

PLACE C6 IN THE 

MICROPROCESSOR 

SOCKET CAVITY

FOR T < 45°C:

C6 = 24 × 1µF Y5V 

CERAMIC SURFACE 

MOUNT CAPACITORS.

Q1

IRFZ24

C3

10pF

C6*

24µF

Ultrafast Transient Response 5V to 3.3V Low Dropout Regulator

(For Schematic Including Current Limit, See Typical Applications)

50mV/DIV

2A/DIV

100µs/DIV

1575/77 TA02

Transient Response for

0.2A to 5A Output Load Step

■

Pentium

Processor Supplies

■

PowerPC

Supplies

■

5V to 3.XXV or 3.3V to 2.XXV Microprocessor Supplies

■

GTL Termination

■

Low Voltage Logic Supplies

LT1575CN8/LT1575CS8 Adjustable

LT1575CN8-1.5/LT1575CS8-1.5 1.5V Fixed

LT1575CN8-2.8/LT1575CS8-2.8 2.8V Fixed

LT1575CN8-3.3/LT1575CS8-3.3 3.3V Fixed

LT1575CN8-3.5/LT1575CS8-3.5 3.5V Fixed

LT1575CN8-5/LT1575CS8-5 5V Fixed

LT1577CS-ADJ/ADJ Adjustable, Adjustable

LT1577CS-3.3/ADJ 3.3V Fixed, Adjustable

LT1577CS-3.3/2.8 3.3V Fixed, 2.8V Fixed

Consult factory for additional output voltage combinations available

in the LT1577.

APPLICATIONS

DESCRIPTION

■

UltraFast

Transient Response

Eliminates

Tantalum and Electrolytic Output Capacitors

■

FET R

DS(ON)

Defines Dropout Voltage

■

1% Reference/Output Voltage Tolerance Over

Temperature

■

Typical Load Regulation: 1mV

■

High Side Sense Current Limit

■

Multifunction Shutdown Pin with Latchoff

FEATURES

The LT

1575/LT1577 are single/dual controller ICs that

drive low cost external N-channel MOSFETs as source

followers to produce ultrafast transient response, low

dropout voltage regulators.

The LT1575/LT1577 achieve unprecedented transient-

load performance by eliminating expensive tantalum or

bulk electrolytic output capacitors in the most demanding

modern microprocessor applications. Precision-trimmed

adjustable and fixed output voltage versions accommo-

date any required microprocessor power supply voltage.

Selection of the N-channel MOSFET R

DS(ON)

allows very

low dropout voltages to be achieved.

Unique protection features include a high side current

limit amplifier that activates a fault protection timer

circuit. A multifunction Shutdown pin provides either

current limit time-out with latchoff, overvoltage protec-

tion, thermal shutdown or a combination of these func-

tions. The LT1575 is available in 8-pin SO or PDIP and the

LT1577 is available in 16-pin narrow body SO.

UltraFast is a trademark of Linear Technology Corporation.

Pentium is a registered trademark of Intel Corporation.

PowerPC is a trademark of IBM Corporation.

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

Summary of content (20 pages)

PAGE 1
LT1575/LT1577 Ultrafast Transient Response, Low Dropout Regulators Adjustable and Fixed U DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ UltraFastTM Transient Response Eliminates Tantalum and Electrolytic Output Capacitors FET RDS(ON) Defines Dropout Voltage 1% Reference/Output Voltage Tolerance Over Temperature Typical Load Regulation: 1mV High Side Sense Current Limit Multifunction Shutdown Pin with Latchoff The LT®1575/LT1577 are single/dual controller ICs that drive low cost external N-channel MOSFETs as sourc
PAGE 2
LT1575/LT1577 W W W AXI U U ABSOLUTE RATI GS (Note 1) VIN, IPOS, INEG ...................................................... 22V SHDN ....................................................................... VIN Operating Ambient Temperature Range ..... 0°C to 70°C Junction Temperature (Note 2) ................ 0°C to 100°C Storage Temperature Range ................ – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................
PAGE 3
LT1575/LT1577 ELECTRICAL CHARACTERISTICS TA = 25°C, VIN = 12V, GATE = 6V, IPOS = INEG = 5V, SHDN = 0.75V unless otherwise noted. SYMBOL PARAMETER IQ Supply Current VFB LT1575 Reference Voltage VOUT CONDITIONS MIN TYP MAX ● 5 12 19 mA ● – 0.6 – 1.0 1.210 1.210 0.6 1.0 % % ● – 0.6 – 1.0 1.500 1.500 0.6 1.0 % % ● – 0.6 – 1.0 2.800 2.800 0.6 1.0 % % ● – 0.6 – 1.0 3.300 3.300 0.6 1.0 % % ● – 0.6 – 1.0 3.500 3.500 0.6 1.0 % % ● – 0.6 – 1.0 5.000 5.000 0.6 1.
PAGE 4
LT1575/LT1577 U W TYPICAL PERFORMANCE CHARACTERISTICS Adjustable LT1575 VREF vs Temperature 1.210 1.208 1.206 1.204 1.485 –75 –50 –25 0 25 50 75 100 125 150 175 TEMPERATURE (°C) 2.828 2.824 2.800 2.816 2.812 2.808 2.804 2.800 2.796 2.792 2.788 2.784 2.780 2.776 2.772 –75 –50 –25 0 25 50 75 100 125 150 175 TEMPERATURE (°C) 1575/77 G04 VIN = 20V VIN = 12V VIN = 8V 1575/77 G03 LT1575-3.3 VOUT vs Temperature 3.333 3.327 3.321 3.315 3.309 3.303 3.297 3.291 3.285 3.279 3.273 3.
PAGE 5
LT1575/LT1577 U W TYPICAL PERFORMANCE CHARACTERISTICS Error Amplifier Large-Signal Voltage Gain vs Temperature VREF/VOUT Line Regulation vs Temperature 0.030 0.020 0.015 0.010 0.005 115 ERROR AMPLIFIER GAIN AND PHASE LARGE-SIGNAL VOLTAGE GAIN (dB) LINE REGULATION (%/V) 0.025 110 105 100 95 90 85 80 75 1575/77 G10 GAIN 50 0 1k NO LOAD 2.25 2.00 1.75 1.50 100k 1M FREQUENCY (Hz) 10M 3.0 1000 2.5 900 1.25 1.00 –75 – 50 –25 0 25 50 75 100 125 150 175 TEMPERATURE (°C) 2.0 1.
PAGE 6
LT1575/LT1577 U W TYPICAL PERFORMANCE CHARACTERISTICS SHDN Low Clamp Voltage vs Temperature SHDN Source Current vs Temperature –10 7.0 – 11 6.5 6.0 5.5 5.0 4.5 4.0 3.5 0.25 SHDN LOW CLAMP VOLTAGE (V) 7.5 SHDN SOURCE CURRENT (µA) SHDN SINK CURRENT (µA) SHDN Sink Current vs Temperature – 12 – 13 – 14 – 15 – 16 – 17 – 18 3.0 – 19 2.5 –75 – 50 –25 0 25 50 75 100 125 150 175 TEMPERATURE (°C) – 20 –75 – 50 –25 0 25 50 75 100 125 150 175 TEMPERATURE (°C) 1575/77 G18 0.20 0.15 0.10 0.
PAGE 7
LT1575/LT1577 U U U PIN FUNCTIONS SHDN (Pin 1): This is a multifunction shutdown pin that provides GATE drive latchoff capability. A 15µA current source, that turns on when current limit is activated, charges a capacitor placed in series with SHDN to GND and performs a current limit time-out function. The pin is also the input to a comparator referenced to VREF (1.21V). When the pin pulls above VREF, the comparator latches the gate drive to the external MOSFET off.
PAGE 8
LT1575/LT1577 W BLOCK DIAGRAM LT1575 Adjustable Voltage VTH1 50mV + ILIM AMP OR1 SW1 NORMALLY OPEN SHDN IPOS + – I1 15µA INEG – D1 + COMP1 I2 5µA R2 5k Q6 – D2 – COMP2 100mV HYSTERESIS + OR2 SW2 NORMALLY CLOSED + START-UP VREF 1.
PAGE 9
LT1575/LT1577 W BLOCK DIAGRAM LT1575 Fixed Voltage IPOS + ILIM AMP OR1 SW1 NORMALLY OPEN – D1 + – I1 15µA VTH1 50mV INEG SHDN – COMP4 COMP1 R2 5k Q6 + – + – D2 + VTH3 500mV 100mV HYSTERESIS I2 5µA – COMP2 OR2 SW2 NORMALLY CLOSED + + START-UP VREF 1.
PAGE 10
LT1575/LT1577 U W U U APPLICATIONS INFORMATION Introduction The current generation of microprocessors place stringent demands on the power supply that powers the processor core. These microprocessors cycle load current from near zero to amps in tens of nanoseconds. Output voltage tolerances as low as ±100mV include transient response as part of the specification. Some microprocessors require only a single output voltage from which the core and I/O circuitry operate.
PAGE 11
LT1575/LT1577 U W U U APPLICATIONS INFORMATION Reference voltage accuracy for the adjustable version and output voltage accuracy for the fixed voltage versions are specified as ±0.6% at room temperature and as ±1% over the full operating temperature range. This places the LT1575/LT1577 family among a select group of regulators with a very tightly specified output voltage tolerance. The accurate 1.21V reference is tied to the noninverting input of the main error amplifier in the feedback control loop.
PAGE 12
LT1575/LT1577 U W U U APPLICATIONS INFORMATION diagram and clamps the positive swing of the COMP node in the main error amplifier to a voltage that provides an output load current of 50mV/RSENSE. This action continues as long as the output current overload persists. The second event is that a timer circuit activates at the SHDN pin. This pin is normally held low by a 5µA active pull-down that limits to ≈ 100mV above ground.
PAGE 13
LT1575/LT1577 U W U U APPLICATIONS INFORMATION very large current spike as soon as the 5V supply started to ramp up. However, undervoltage lockout circuit COMP2, which monitors the IPOS supply voltage, holds Q3 on and pulls the COMP pin low until the IPOS voltage increases to greater than the internal 1.21 reference voltage. The undervoltage lockout circuit then smoothly releases the COMP pin and allows the output voltage to come up in dropout from the input supply voltage.
PAGE 14
LT1575/LT1577 U TYPICAL APPLICATIONS N Setting Output Voltage with the Adjustable LT1575 Using “Sense-Less” Current Limit VOUT R3 10Ω SHDN R2 IPOS VCC C1 10µF CT FB INEG R1 Q1 GATE VOUT = 1.21V(1 + R2/R1) VOUT 1575 TA03 Setting Current Limit IPOS Setting Current Limit with Foldback Limiting IPOS VCC VCC R5 10Ω RSENSE* R4 INEG INEG D1 1N4148 D2 1N4148 Q2 GATE GATE VOUT 1575 TA06 Shutdown Time-Out with Reset Q1 VN2222L R1 100k 5V RT1 10k NTC C1* SHDN *C1 = 15µA(t)/1.
PAGE 15
LT1575/LT1577 U TYPICAL APPLICATIONS N Pentium ® II Processor GTL+ Power Supply VTT 1.5V VIN 3.3V 12V + C1 220µF 6.3V R4 75Ω VREF LT1575-1.5 1 RESET 2 C2 0.22µF C3 1µF 3 4 SHDN IPOS VIN INEG GND GATE OUT COMP 8 7 6 R2 3.9Ω 5 R1 0.005Ω R5 150Ω Q1 IRFZ24 RX R8 100Ω R3 4.99k C5 1000pF C4 10pF NOTE: LTC RECOMMENDS CENTRALLY LOCATING THE LT1575-1.5 OUTPUT TO MINIMIZE VTT DISTRIBUTION DROPS AND USING SEPARATE VREF GENERATORS AT EACH BUS END R6 75Ω R9 100Ω VREF C6 0.1µF C7 0.
PAGE 16
LT1575/LT1577 U TYPICAL APPLICATIONS N 12V to 3.3V/9A (14A Peak) Hybrid Regulator LT1575 1 2 12V 3 4 C6 0.1µF SHDN IPOS VIN INEG GND GATE OUT COMP 8 7 Q1 IRLZ44 6 5 C21, 10pF 12V + C11 150µF 16V + C12 150µF 16V + C13 150µF 16V + 9 1 C8, 68pF 2 C7, 0.1µF C10, 1000pF C9 1500pF R5 16.5k C14 150µF 16V C17 1µF 13 VIN EXTVCC TG COSC SW RUN/SS BOOST LTC1435 12 ITH INTVCC 4 11 6 BG SGND S+ VOS S PGND 10 R1 2.1k, 1% C16 1µF R2 1.21k 1% L1 4µH C3, 0.
PAGE 17
LT1575/LT1577 U TYPICAL APPLICATIONS N 3.3V to 2.8V ±100mV at 5.7A with Sense-Less Current Limit and Timer Latchoff INPUT 3.3V + + C1 330µF 6.3V C2 330µF 6.3V 12V R2 10Ω FAULT RESET LT1575-2.8 1 RTN 2 3 4 C3 680pF SHDN IPOS VIN INEG GND GATE OUT COMP C6 0.1µF C7 10µF 8 7 6 Q1 IRL3303 5 VCORE 2.8V R1 4.7k C5 22pF + C4 1000pF C8 TO C31* 1µF 1575/77 TA14 *X7R CERAMIC 0805 CASE U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted.
PAGE 18
LT1575/LT1577 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) *DIMENSION DOES NOT INCLUDE MOLD FLASH.
PAGE 19
LT1575/LT1577 U PACKAGE DESCRIPTION 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) 16 15 14 13 12 11 10 9 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) 2 3 4 5 6 0.053 – 0.069 (1.346 – 1.752) 0.008 – 0.010 (0.203 – 0.254) 0.014 – 0.019 (0.355 – 0.483) 8 0.004 – 0.010 (0.101 – 0.254) 0° – 8° TYP 0.016 – 0.
PAGE 20
LT1575/LT1577 U TYPICAL APPLICATION LT1577 Split Plane System FAULT RESET INPUT 5V C1 330µF 6.3V + + 1/2 LT1577 1/2 LT1577 1 2 12V 3 C3 0.33µF 4 SHDN1 IPOS1 VIN1 INEG1 GND1 GATE1 OUT-3.3 COMP1 16 5 15 6 14 13 C5 10pF C4 1µF C2 330µF 6.3V R1 3.9Ω 7 Q1 IRFZ24 R2 3.9k C6 1500pF 8 SHDN2 IPOS2 VIN2 INEG2 GND2 GATE2 OUT-2.8 COMP2 VI/O 3.3V 12 11 10 R5 3.9Ω 9 VCORE 2.8V R6 7.