LT1248IS Linear Technology, LT1248IS Datasheet - Page 6

• Manufacturer Part Number: LT1248IS
• Description: IC PFC CTRLR AVERAGE CURR 16SOIC
• Manufacturer: Linear Technology

Specifications of LT1248IS

• Mode: Average Current
• Frequency - Switching: 300kHz
• Current - Startup: 250µA
• Voltage - Supply: 15.5 V ~ 27 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

PI FU CTIO S
LT1248
TYPICAL PERFOR
Pin 1 (GND).
Pin 2 (PK
comparator is GND. To set current limit, a resistor divider
can be connected from V
Pin 3 (CA
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 CA
the modulator has zero duty cycle.
Pin 4 (I
amplifier. This pin is clamped at – 0.6V by an ESD protec-
tion diode.
Pin 5 (M
current output and the noninverting input of the current
amplifier. This pin is clamped at – 0.6V and 2V.
Pin 6 (I
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 32k resistor is in series with the
current input, so that a lowpass RC can be used to filter out
the switching noise from the high impedance lines.
6
U
AC
SENSE
): This is the AC line voltage sensing input to the
OUT
OUT
LIM
U
): This is the output of the current amplifier
): This is the inverting input of the current
): The threshold of the peak current limit
): This is the multiplier high impedance
–100
–20
–40
–60
–80
120
100
80
60
40
20
0
R
0
SET
U
Voltage vs Current
–0.2
REF
R
SET
W
–0.4
to current sense resistor.
CURRENT (mA)
A
U
–0.6
CE
T
T
T
J
J
J
= 125 C
= 25 C
= –55 C
–0.8
C
HARA TERISTICS
1248 G16
OUT
–1.0
is low,
C
Pin 7 (VA
amplifier. The output is clamped at 13.5V. When the
output goes below 2.5V, the multiplier output current is
zero.
Pin 8 (OVP): This is the input to the overvoltage compara-
tor. The threshold is 1.05 times the reference voltage.
When the comparator trips, the multiplier is quickly inhib-
ited and outputs no current. Figure 4 in the Applications
Information section shows how to set overvoltage thresh-
old with only one additional resistor.
Pin 9 (V
or EN/SYNC goes low, V
most of the internal circuity and can source up to 5mA
externally.
Pin 10 (EN/SYNC): This pin has two functions. When it
goes below 2.6V, the chip goes into shutdown mode and
draws little current. Pulses at this pin that go below the 5V
threshold will synchronize the chip. The synchronizing
pulses should have an on-time of at least 200ns for the
LT1248 resetting circuit to work.
Pin 11 (V
amplifier.
REF
SENSE
–360
–300
–240
–180
–120
–60
120
180
240
300
OUT
60
): This is the 7.5V reference. When either V
0
PK
): This is the output of the voltage error
): This is the inverting input to the voltage
–0.8
LIM
Pin Characteristics
–0.4
PK
LIM
REF
VOLTAGE (V)
0
will stay at 0V. V
0.4
T
T
T
J
J
J
= 125 C
= 25 C
= –55 C
0.8
1248 G17
REF
biases
CC