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參數(shù)資料
| 型號： | LTC3731IUH |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 3-Phase, 600kHz, Synchronous Buck Switching Regulator Controller |
| 中文描述： | 5 A SWITCHING CONTROLLER, 750 kHz SWITCHING FREQ-MAX, PQCC32 |
| 封裝： | 5 X 5 MM, PLASTIC, M0-220WHHD, QFN-32 |
| 文件頁數(shù)： | 7/16頁 |
| 文件大小： | 200K |
| 代理商： | LTC3731IUH |
LT3782
7
3782fa
APPLICATIU
Operation
The LT3782 is a two phase constant frequency current
mode boost controller. Switching frequency can be pro-
grammed up to 500kHz. During normal switching cycles,
the two channels are controlled by internal flip-flop and are
180 degrees out of phase.
Referring to the Block Diagram, the LT3782 basic func-
tions include a transconductance amplifer (gm) to regu-
late the output voltage and to control the current mode
PWM current loop. It also includes the necessary logic and
flip-flop 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 amplified
then compared to the error amplifier output V
C
to turn the
switch off. The phase delay of the second channel is
controlled by the divide-by-two D flip-flop and is exactly
180 degrees out of phase of the first channel. With a
resistor divider connected to the FB pin, the output voltage
is programmed to the desired value. The 10V gate drivers
are sufficient to drive most high power N-Channel MOSFET
in many industrial applications.
Additional important features include shutdown, current
limit, soft-start, synchronization and programmable maxi-
mum duty cycle. Additional slope compensation can be
added also.
W
U
U
Output Voltage Programming
With a 2.44V feedback reference voltage V
REF
, the output
V
OUT
is programmed by a resistor divider as shown in the
Block Diagram.
V
R
R
OUT
F
F
=
+
2.
1
2
Soft-Start and Shutdown
During soft-start, the voltage on the SS pin (V
SS
) controls
the output voltage. The output voltage thus ramps up
following V
SS
. The effective range of V
SS
is from 0V to
2.44V. The typical time for the output to reach the pro-
grammed level is
t
C
V
A
=
μ
.44
10
C is the capacitor connected from the SS pin to Gnd.
Undervoltage Lockout and Shutdown
Only when V
RUN
is higher than 2.45V V
GBIAS
will be active
and the switching enabled. The LT3782 goes into low
current shutdown when V
RUN
is below 0.3V. A resistor
divider can be used on RUN pin to set the desired V
CC
undervoltage lockout voltage. A 120mV 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
FREQ
from pin R
SET
to ground.
For f
SET
= 250kHz, R
FREQ
= 80k
Once the switching frequency f
SET
is chosen, R
FREQ
can be
found from the Switching Frequency vs R
FREQ
graph
found under the Typical Electrical 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
SYSTEM
,
the synchronizing frequency f
SYNC
should be two times
f
SYSTEM
, and the LT3782 switching frequency f
SET
should
be set below 80% of f
SYSTEM
.
f
SYNC
= 2f
SYSTEM
and f
SET
< (f
SYSTEM
0.8)
For example, to synchronize the LT3782 to 200kHz system
frequency f
SYSTEM
, f
SYNC
needs to be set at 400kHz and
f
SET
needs to be set at 160kHz. From the Switching
Frequency vs R
FREQ
graph found under the Typical Electri-
cal Characteristics section, R
FREQ
= 130k.
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