LT1244IS8 Linear Technology, LT1244IS8 Datasheet - Page 7

• Manufacturer Part Number: LT1244IS8
• Description: IC PWM CURRENT MODE HI-SPD 8SOIC
• Manufacturer: Linear Technology

Specifications of LT1244IS8

• Pwm Type: Current Mode
• Number Of Outputs: 1
• Frequency - Max: 500kHz
• Duty Cycle: 48%
• Voltage - Supply: 11 V ~ 25 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: Yes
• Operating Temperature: -40°C ~ 100°C
• Package / Case: 8-SOIC (3.9mm Width)
• Frequency-max: 500kHz
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

PI
COMP (Pin 1): Compensation Pin. This pin is the output of
the Error Amplifier and is made available for loop compen-
sation. It can also be used to adjust the maximum value of
the current sense clamp voltage to less than 1V. This pin
can source a minimum of 0.5mA (0.8mA typ) and sink a
minimum of 2mA (4mA typ)
FB (Pin 2) Voltage Feedback Pin. This pin is the inverting
input of the error amplifier. The output voltage is normally
fed back to this pin through a resistive divider. The non-
inverting input of the error amplifier is internally commit-
ted to a 2.5V reference point.
I
current sense comparator. The trip point of the compara-
tor is set by, and is proportional to, the output voltage of
the Error Amplifier.
R
are set by connecting a resistor (R
and a capacitor (C
Oscillator
The LT1241 series devices are fixed frequency current
mode pulse width modulators. The oscillator frequency
and the oscillator discharge current are both trimmed and
tightly specified to minimize the variations in frequency
and deadtime. The oscillator frequency is set by choosing
a resistor and capacitor combination, R
combination will determine both the frequency and the
maximum duty cycle. The resistor R
V
A
SENSE
T
START-UP
DEVICE
LT1241
LT1242
LT1243
LT1244
LT1245
REF
/C
PPLICATI
U
T
(Pin 8) to the R
(Pin 4): The oscillator frequency and the deadtime
FU
(Pin 3): Current Sense Pin. This is the input to the
U
THRESHOLD
OPERATING
MINIMUM
C
9.6V
8.4V
8.4V
16V
16V
TI
O
O
T
) from R
U
T
U
/C
S
S
T
MAXIMUM
VOLTAGE
pin (Pin 4). The capacitor C
I FOR ATIO
U
7.6V
7.6V
7.6V
10V
10V
T
/C
T
to GND.
T
DUTY CYCLE REPLACES
) from V
W
T
100%
100%
is connected from
50%
50%
50%
T
and C
REF
T
. This RC
U
to R
UC1842
UC1843
UC1844
UC1845
NONE
T
T
/C
is
T
The rise time of the oscillator waveform is set by the RC
time constant of R
the output deadtime, is set by a combination of the RC time
constant and the oscillator sink current (8.2mA typ).
GND (Pin 5): Ground.
OUTPUT (Pin 6): This pin is the output of a high current
totem pole output stage. It is capable of driving up to 1A
of current into a capacitive load such as the gate of a
MOSFET.
V
IC.
V
IC. The reference output is used to supply charging current
to the external timing resistor R
biasing to a large portion of the internal circuitry, and is
used to generate several internal reference levels includ-
ing the V
connected from the R
current for C
discharge current for C
the current supplied by R
LT124X. The discharge current of the device is trimmed to
8.2mA. For large values of R
determined by the discharge current of the device and the
value of C
effect on the discharge time of C
cycle capacitor C
discharged to approximately 1.1V. The output is enabled
during the charge time of C
during the discharge time of C
is equal to the discharge time of C
cycle is limited by controlling the deadtime of the oscilla-
tor. There are many combinations of R
yield a given oscillator frequency, however there is only
one combination that will yield a specific deadtime at that
frequency. Curves of oscillator frequency and deadtime
CC
REF
(Pin 7): This pin is the positive supply of the control
(Pin 8): Reference. This is the reference output of the
FB
T
. As the value of R
level and the current sense clamp voltage.
T
is determined by the value of R
T
T
is charged to approximately 2.8V and
and C
T
T
/C
T
is set by the difference between
T
T
and the discharge current of the
. The fall time, which is equal to
T
pin to ground. The charging
T
and disabled, in an off state,
T
is reduced it will have more
. The deadtime of the circuit
T
T
. The reference provides
LT1241 Series
discharge time will be
T
T
. During an oscillator
. The maximum duty
T
and C
T
that will
T
. The
7