LTC1624CS8 Linear Technology, LTC1624CS8 Datasheet - Page 5

• Manufacturer Part Number: LTC1624CS8
• Description: IC SW REG CONTROLLER N-CH 8-SOIC
• Manufacturer: Linear Technology
• Type: Step-Down (Buck), Step-Up (Boost), Inverting, Sepicr

Specifications of LTC1624CS8

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.19 ~ 30 V
• Current - Output: 2A
• Frequency - Switching: 200kHz
• Voltage - Input: 3.5 ~ 36 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

PIN
TG (Pin 6): High Current Gate Drive for Top N-Channel
MOSFET. This is the output of a floating driver with a
voltage swing equal to INTV
switch node voltage SW.
BOOST (Pin 7): Supply to Topside Floating Driver. The
bootstrap capacitor C
OPERATIO
Main Control Loop
The LTC1624 uses a constant frequency, current mode
architecture. During normal operation, the top MOSFET is
turned on each cycle when the oscillator sets the RS latch
and turned off when the main current comparator I
the RS latch. The peak inductor current at which I
the RS latch is controlled by the voltage on the I
pin, which is the output of error amplifier EA. The V
described in the pin functions, allows EA to receive an
output feedback voltage from an external resistive divider.
When the load current increases, it causes a slight
decrease in V
turn causes the I
average inductor current matches the new load current.
While the top MOSFET is off, the internal bottom MOSFET
is turned on for approximately 300ns to 400ns to recharge
the bootstrap capacitor C
The top MOSFET driver is biased from the floating boot-
strap capacitor C
The dropout detector counts the number of oscillator
cycles that the top MOSFET remains on and periodically
forces a brief off period to allow C
The main control loop is shut down by pulling the I
pin below its 1.19V clamp voltage. Releasing I
allows an internal 2.5 A current source to charge com-
pensation capacitor C
reaches 0.8V the main control loop is enabled with the I
RUN voltage pulled up by the error amp. Soft start can be
U
FUNCTIONS
U
FB
relative to the 1.19V reference, which in
B
U
TH
that is recharged during each off cycle.
/RUN voltage to increase until the
U
(Refer to Functional Diagram)
C
B
. When the I
is returned to this pin. Voltage
B
.
CC
superimposed on the
B
to recharge.
TH
/RUN pin voltage
TH
TH
TH
1
1
FB
resets
resets
/RUN
/RUN
/RUN
pin,
TH
/
swing at this pin is from INTV
down applications. In non step-down topologies the volt-
age at this pin is constant and equal to INTV
V
Current Comparator. Must be closely decoupled to ground.
implemented by ramping the voltage on the I
from 1.19V to its 2.4V maximum (see Applications Infor-
mation section).
Comparator OV guards against transient output over-
shoots >7.5% by turning off the top MOSFET and keeping
it off until the fault is removed.
Low Current Operation
The LTC1624 is capable of Burst Mode operation in which
the external MOSFET operates intermittently based on
load demand. The transition to low current operation
begins when comparator B detects when the I
voltage is below 1.5V. If the voltage across R
not exceed the offset of I
full cycle, then on following cycles the top and internal
bottom drives are disabled. This continues until the I
voltage exceeds 1.5V, which causes drive to be returned to
the TG pin on the next cycle.
INTV
Power for the top and internal bottom MOSFET drivers is
derived from V
power. To power the top driver in step-down applications
an internal high voltage diode recharges the bootstrap
capacitor C
A small internal N-channel MOSFET pulls the switch node
(SW) to ground each cycle after the top MOSFET has
turned off ensuring the bootstrap capacitor is kept fully
charged.
IN
(Pin 8): Main Supply Pin and the (+) Input to the
CC
Power/Boost Supply
B
during each off cycle from the INTV
IN
. An internal regulator supplies INTV
2
(approximately 20mV) for one
CC
to V
IN
+ INTV
LTC1624
CC
TH
SENSE
if SW = 0V.
CC
CC
/RUN pin
TH
in step-
supply.
/RUN
does
5
TH
CC