LT3782EFE-PBF LINER [Linear Technology], LT3782EFE-PBF Datasheet - Page 8

• Manufacturer Part Number: LT3782EFE-PBF
• Description: 2-Phase Step-UP DC/DC Controller
• Manufacturer: LINER [Linear Technology]

LT3782
APPLICATIONS INFORMATION
8
Operation
The LT3782 is a two phase constant frequency current mode
boost controller. Switching frequency can be programmed
up to 500kHz. During normal switching cycles, the two
channels are controlled by internal fl ip-fl ops and are 180
degrees out-of-phase.
Referring to the Block Diagram, the LT3782’s basic func-
tions include a transconductance amplifer (g
the output voltage and to control the current mode PWM
current loop. It also includes the necessary logic and fl ip-
fl op to control the PWM switching cycles, two high speed
gate drivers to drive high power N-Channel MOSFETs, and
2-phase control signals to drive external gate drivers for
optional synchronous operation.
In normal operation, each switching cycle starts with a
switch turn-on. The inductor current of each channel is
sampled through the current sense resistor and amplifi ed
then compared to the error amplifi er output V
the switch off. The phase delay of the second channel is
controlled by the divide-by-two D fl ip-fl op and is exactly
180 degrees out-of-phase of the fi rst channel. With a re-
sistor divider connected to the FB pin, the output voltage
is programmed to the desired value. The 10V gate drivers
are suffi cient to drive most high power N-channel MOSFET
in many industrial applications.
Additional important features include shutdown, cur-
rent limit, soft-start, synchronization and programmable
maximum duty cycle. Additional slope compensation can
be added also.
Output Voltage Programming
With a 2.44V feedback reference voltage V
V
the Block Diagram.
OUT
V
OUT
is programmed by a resistor divider as shown in
= 2.44 1+
R
R
F2
F1
REF
m
) to regulate
, the output
C
to turn
Soft-Start and Shutdown
During soft-start, the voltage on the SS pin (V
the output voltage. The output voltage thus ramps up fol-
lowing V
The typical time for the output to reach the programmed
level is
C is the capacitor connected from the SS pin to Gnd.
Undervoltage Lockout and Shutdown
Only when V
tive and the switching enabled. The LT3782 goes into low
current shutdown when V
divider can be used on RUN pin to set the desired V
undervoltage lockout voltage. 80mV of hysteresis is built
in on RUN pin thresholds.
Oscillation Frequency Setting and Synchronization
The switching frequency of LT3782 can be set up to 500kHz
by a resistor R
Once the switching frequency f
found from the Switching Frequency vs R
under the Typical Performance Characteristics section.
Note that because of the 2-phase operation, the internal
oscillator is running at twice the switching frequency. To
synchronize the LT3782 to the system frequency f
the synchronizing frequency f
f
be set below 80% of f
For example, to synchronize the LT3782 to 200kHz system
frequency f
needs to be set at 160kHz. From the Switching Frequency
vs R
Characteristics section, R
SYSTEM
For f
f
t =
SYNC
FREQ
C • 2.44V
SET
, and the LT3782 switching frequency f
10μA
SS
= 2f
graph found under the Typical Performance
. The effective range of V
SYSTEM
= 250kHz, R
SYSTEM
RUN
FREQ
is higher than 2.45V V
, f
SYNC
from pin R
and f
SYSTEM
FREQ
needs to be set at 400kHz and f
SET
FREQ
RUN
= 80k
.
< (f
SET
SYNC
SET
= 130k.
is below 0.3V. A resistor
SYSTEM
is chosen, R
to ground.
SS
should be two times
is from 0V to 2.44V.
FREQ
GBIAS
• 0.8)
graph found
SS
FREQ
SET
will be ac-
) controls
SYSTEM
should
can be
3782ff
SET
CC
,