LT1509CSW datasheet(6/16 Pages) LINER

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LT1509

TYPICAL PERFORMANCE CHARACTERISTICS

RSET Voltage vs Current

PKLIM Pin Characteristics

PFC SECTION

GTDR1 (Pin 1): The PFC MOSFET gate driver is a fast

totem pole output which is clamped at 15V. Capacitive

loads like the MOSFET gates may cause overshoot. A gate

series resistor of at least 5

Ω will prevent the overshoot.

GND2 (Pin 2): Power Ground. High current spikes occur

in this line when either GTDR1 or GTDR2 switches low.

GND1 (Pin 3): Analog Ground.

CSET (Pin 4): The capacitor from this pin to GND and RSET

determines oscillator frequency. The oscillator ramp is 5V

and the frequency = 1.5/(RSET CSET).

PKLIM (Pin 5): The threshold of the peak current limit

comparator is GND. To set current limit, a resistor divider

can be connected from VREF to current sense resistor.

CAOUT (Pin 6): This is the output of the current amplifier

that senses and forces the line current to follow the

reference signal that comes from the multiplier by com-

manding the pulse width modulator. When CAOUT is low,

the modulator has zero duty cycle.

ISENSE (Pin 7): This is the inverting input of the current

amplifier. This pin is clamped at – 0.6V by an ESD protec-

tion diode.

MOUT (Pin 8): This is the multiplier high impedance

current output and the noninverting input of the current

amplifier. This pin is clamped at – 0.6V and 3V.

IAC (Pin 9): This is the AC line voltage sensing input to the

multiplier. It is a current input that is biased at 2V to

minimize the crossover dead zone caused by low line

voltage. At the pin, a 25k resistor is in series with the

current input, so that a lowpass RC can be used to filter out

the switching noise coming down from the line with a high

line impedance environment.

VAOUT (Pin 10): This is the output of the voltage error

amplifier. The output is clamped at 13.5V. When the

output goes below 2.5V, the multiplier output current is

zero.

OVP (Pin 11): This is the input to the overvoltage com-

parator. The threshold is 1.05 times the reference voltage.

When the comparator trips, the multiplier, which is quickly

inhibited, blanks PFC switching to prevent further over-

shoot. This pin is also the input to the PWMOK comparator

that releases the PWM soft start (SS2) after the PFC output

gets close to the final voltage and has a hysteresis of

approximately 150V for 382V PFC output.

VREF (Pin 12): This is the 7.5V reference. When VCC goes

low, VREF will stay at 0V. VREF biases most of the internal

circuitry and can source up to 5mA externally.

VSENSE (Pin 14): This is the inverting input to the voltage

amplifier.

(For application help with the PFC portion of this chip, see the LT1248 data sheet)

PIN FUNCTIONS

RSET CURRENT (mA)

120

100

–20

–40

–60

–80

–100

LT1509 • TPC12

–1.0

–0.8

–0.6

–0.4

–0.2

TJ = 125°C

TJ = 25°C

TJ = –55°C

PKLIM VOLTAGE (V)

–360

–300

–240

–180

–120

– 60

120

180

240

300

LT1509 • TPC13

0.8

0.4

–0.4

–0.8

TJ = 125°C

TJ = 25°C

TJ = –55°C

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