lt3845a Linear Technology Corporation, lt3845a Datasheet - Page 8

• Manufacturer Part Number: lt3845a
• Description: Lt3845a - High Voltage Synchronous Current Mode Step-down Controller With Adjustable Operating Frequency
• Manufacturer: Linear Technology Corporation

LT3845A
TG: The TG pin is the bootstrapped gate drive for the top
N-Channel MOSFET. Since very fast high currents are driven
from this pin, connect it to the gate of the power MOSFET
with a short and wide, typically 0.02” width, PCB trace to
minimize inductance.
V
voltage corresponds to the maximum (peak) switch
current per oscillator cycle. The error amplifier is typically
configured as an integrator by connecting an RC network
from the V
pole for the converter regulation control loop. Specific
integrator characteristics can be configured to optimize
transient response. When Burst Mode operation is enabled
(see Pin 4 description), an internal low impedance clamp on
the V
limits the negative excursion of the pin voltage. Therefore,
this pin cannot be pulled low with a low impedance source.
If the V
a 1kΩ series resistance.
V
node. Use a low ESR, 1µF or greater ceramic capacitor to
decouple this node to PGND. Most internal IC functions are
PIN FUNCTIONS
8
C
CC
: The V
: The V
C
pin is set at 100mV below the burst threshold, which
C
pin must be externally manipulated, do so through
C
C
CC
pin is the output of the error amplifier whose
pin to SGND. This circuit creates the dominant
pin is the internal bias supply decoupling
powered from this bias supply. An external diode connected
from V
capacitor during the off-time of the main power switch.
Back driving the V
source, such as the V
increases overall efficiency and reduces power dissipation
in the IC. In shutdown mode this pin sinks 20µA until the
pin voltage is discharged to 0V.
V
connected to the supply output voltage via a resistive divider.
The V
of the error amplifier. In regulation, V
V
decoupled to SGND with a low ESR capacitor (at least
0.1µF) located close to the pin.
Exposed Pad (SGND) (TSSOP Only): The exposed
leadframe is internally connected to the SGND pin. Solder
the exposed pad to the PCB ground for electrical contact
and optimal thermal performance.
FB
IN
: The V
: The output voltage feedback pin, V
FB
CC
pin is internally connected to the inverting input
to the BOOST pin charges the bootstrapped
IN
pin is the main supply pin and should be
CC
OUT
pin from an external DC voltage
output of the regulator supply,
FB
is 1.231V.
FB
, is externally
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