Datasheet

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LT1248

Power Factor Controller

–

200µA

OUT

16V TO 10V

2.6V/

2.2V

7.5V

7.9V

12µA

REF

–

2.2V

32k

7µA

7.5V

REF

–

0.7V

ONE SHOT

200ns

OSC

SET

1214

OVP

SENSE

EN/SYNC

OUT

SENSE

OUT

LIM

RUN

1 6V

GND

–

GTDR

1248 BD

SYNC

The LT

1248 provides active power factor correction for

universal off-line power systems. By using fixed high

frequency PWM current averaging, without the need for

slope compensation, the LT1248 achieves far lower line

current distortion with a smaller magnetic element than

systems that use either peak-current detection or zero

current switching approaches in both continuous and

discontinuous modes of operation.

The LT1248 uses a multiplier containing a square gain

function from the voltage amplifier to reduce the AC gain

at light output load and thus maintains low line current

distortion and high system stability. The LT1248 also

provides filtering capability to reject line switching noise

which can cause instability when fed into the multiplier.

Line current dead zone is minimized with low bias voltage

at the current input to the multiplier.

The LT1248 provides many protection features including

peak current limiting and overvoltage protection, and can

be operated at frequencies as high as 300kHz.

■

High Power Factor Over Wide Load Range

with Line Current Averaging

■

International Operation Without Switches

■

Instantaneous Overvoltage Protection

■

Minimal Line Current Dead Zone

■

Typical 250µA Start-Up Supply Current

■

Rejects Line Switching Noise

■

Synchronization Capability

■

Low Quiescent Current: 9mA

■

Fast 1.5A Peak Current Gate Driver

■

Universal Power Factor Corrected Power Supplies

■

Preregulators Up To 1500W

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

FEATURES

DESCRIPTIO

APPLICATIO S

BLOCK DIAGRA

Summary of content (12 pages)

PAGE 1
LT1248 Power Factor Controller U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO The LT®1248 provides active power factor correction for universal off-line power systems. By using fixed high frequency PWM current averaging, without the need for slope compensation, the LT1248 achieves far lower line current distortion with a smaller magnetic element than systems that use either peak-current detection or zero current switching approaches in both continuous and discontinuous modes of operation.
PAGE 2
LT1248 U U RATI GS W W W W AXI U U ABSOLUTE PACKAGE/ORDER I FOR ATIO (Note 1) Supply Voltage ....................................................... 27V GTDR Current Continuous ..................................... 0.5A GTDR Output Energy(Per Cycle) .............................. 5µJ IAC, RSET, PKLIM Input Current ............................. 20mA VSENSE, EN/SYNC, OVP Input Voltage ................... VMAX ISENSE, MOUT Input Current ..................................
PAGE 3
LT1248 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. Maximum operating voltage (VMAX) = 25V, VCC = 18V, RSET = 15k to GND, CSET = 1nF to GND, IAC = 100µA, ISENSE = 0V, CAOUT = 3.5V, VAOUT = 5V, OVP = 7.5V, no load on any outputs, unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS ● 5 14 30 mA ● – 0.3 1 V 7.
PAGE 4
LT1248 U W TYPICAL PERFOR A CE CHARACTERISTICS Current Amplifier Open-Loop Gain and Phase Voltage Amplifier Open-Loop Gain and Phase 100 0 80 100 –20 0 80 –20 GAIN 40 –60 20 10 100 1k 10k 100k FREQUENCY (Hz) 1M 60 –40 40 –60 –80 20 –100 0 –120 10M –20 PHASE 0 –20 GAIN (dB) –40 –80 PHASE –100 10 1148 G02 Reference Voltage vs Temperature Multiplier Current 7.536 300 7.524 VAOUT = 5.5V VAOUT = 7V 7.512 VAOUT = 6.5V 7.
PAGE 5
LT1248 U W TYPICAL PERFOR A CE CHARACTERISTICS Start-Up Supply Current vs Supply Voltage GTDR Rise and Fall Time SUPPLY CURRENT (µA) TIME (ns) 300 FALL TIME 200 RISE TIME 100 NOTE: GTDR SLEWS BETWEEN 1V AND 16V 0 0 10 20 30 40 LOAD CAPACITANCE (nF) 550 500 500 450 450 400 400 350 300 –55°C 25°C 250 200 125°C 150 250 200 150 50 50 4 2 0 200 6 8 10 12 14 16 18 20 SUPPLY VOLTAGE (V) 1248 G08 600 1000 1800 1400 CSET CAPACITANCE (pF) Shutdown Mode Supply Current and Reference Volta
PAGE 6
LT1248 U W TYPICAL PERFOR A CE CHARACTERISTICS RSET Voltage vs Current PKLIM Pin Characteristics 120 –360 TJ = 125°C TJ = 25°C TJ = –55°C 100 –240 60 PKLIM CURRENT (µA) VRSET – VREF (mV) 80 40 20 0 –20 –40 –180 –120 –60 0 60 120 –60 180 –80 240 –100 0 –0.2 –0.8 –0.4 –0.6 RSET CURRENT (mA) TJ = 125°C TJ = 25°C TJ = –55°C –300 –1.0 1248 G16 300 –0.8 0.4 –0.4 0 PKLIM VOLTAGE (V) 0.8 1248 G17 U U U PI FU CTIO S Pin 1 (GND).
PAGE 7
LT1248 U U U PI FU CTIO S Pin 12 (RSET): A resistor from RSET to GND sets the oscillator charging current and the maximum multiplier output current which is used to limit the maximum line current. IM(MAX) = 3.75V/RSET Pin 13 (SS): Soft-Start. When either VCC or EN/SYNC goes low, the SS pin will stay at 0V. With a capacitor from the pin to GND, the 12µA charging current slowly brings up the SS to 8V; below 7.5V SS is the reference input to the voltage amplifier.
PAGE 8
LT1248 U W U UO APPLICATI S I FOR ATIO ripple fed back to the error amplifier is minimized. Note that switching ripple on the high impedance lines could get into the multiplier from the IAC pin and cause instability. The LT1248 provides an internal 25k resistor in series with the low impedance multiplier current input so that only a capacitor from the IAC pin to GND is needed to filter out the noise.
PAGE 9
LT1248 W U U UO APPLICATI S I FOR ATIO Note that VSENSE is the summing node and it stays at 7.5V. When overshoot occurs on VOUT, the overcurrent from R1 will go through R2 as well as R3. Amplifier feedback will keep VSENSE locked at 7.5V. The equivalent AC resistance, seen by the comparator input pin OVP, is R2 in parallel with R3, which is 10k. Therefore, with the comparator trip level of 1.05VREF and R3 of 20k, the comparator trips when VOUT overshoot exceeds 10%.
PAGE 10
LT1248 U W U UO APPLICATI S I FOR ATIO VOUT/(VCC – 2V) = NP/NS. For 382V VOUT and 18V VCC, Np/Ns ≈ 19. In Figure 6, a new technique for supply voltage eliminates the need for an extra inductor winding. It uses capacitor charge transfer to generate a constant current source which feeds a Zener diode. Current to the Zener is equal to (VOUT – VZ)(C)(f), where VZ is Zener voltage and f is switching frequency. For VOUT = 382V, VZ = 18V, C = 1000pF, and f = 100kHz, Zener current will be 36mA.
PAGE 11
LT1248 UO TYPICAL APPLICATI 300W, 382V Preregulator 90V TO 270V MURH860 750µH* T + VOUT EMI FILTER 6A – 0.47µF 20k RREF 4k 330k 4k 100pF VCC = 18V** 1nF 0.1µF VAOUT VCC + 16V TO 10V – 10 11 1M 2.2V 7.5V OVP + 13 GND 15 VCC – 7µA I 2I I = A B IB M 200µA2 – + CA + R R – 32k – 5V IM + Q GTDR 16 10Ω S RUN + – 12µA SS 1 + 0.7V– 4.7nF 50k PKLIM 2 3 CAOUT + IA – + 7.
PAGE 12
LT1248 U PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. N Package 16-Lead PDIP (Narrow 0.300) (LTC DWG # 05-08-1510) 0.130 ± 0.005 (3.302 ± 0.127) 0.300 – 0.325 (7.620 – 8.255) 0.009 – 0.015 (0.229 – 0.381) ( +0.889 8.255 –0.381 0.045 – 0.065 (1.143 – 1.651) 0.020 (0.508) MIN +0.035 0.325 –0.015 ) 0.770* (19.558) MAX 0.065 (1.651) TYP 0.125 (3.175) MIN 15 14 13 12 11 10 1 2 3 4 5 6 7 9 0.255 ± 0.015* (6.477 ± 0.381) 0.018 ± 0.003 (0.457 ± 0.