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參數(shù)資料
| 型號： | LT3640IUFD#PBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 3.4 A DUAL SWITCHING CONTROLLER, 2350 kHz SWITCHING FREQ-MAX, PQCC28 |
| 封裝： | 5 X 4 MM, LEAD FREE, PLASTIC, MO-220, QFN-28 |
| 文件頁數(shù)： | 5/24頁 |
| 文件大小： | 506K |
| 代理商： | LT3640IUFD#PBF |
LT3640
3640f
Figure 1. Lower Switching Frequency Occurs in High
Voltage Channel When Required On-Time Is Below 50ns
The maximum VIN should not exceed the absolute maxi-
mum rating. For fixed frequency operation, the maximum
VIN is:
V
DC
V
IN MAX
OUT
D
MIN
D
CE
(
) =
+
+
1
Note that the high voltage buck will still regulate at an input
voltage that exceeds VIN(MAX) (up to 35V). However, the
switching frequency will be lowered to satisfy the equa-
tion (Figure 1).
Oncetheinputvoltagereaches36.5V,aninternalovervoltage
lockout (OVLO) circuit is triggered to disable switching ac-
tion (Figure 2). Without switching, the LT3640 can sustain
VIN voltage transients up to 55V for one second.
VIN2 Voltage Range
The low voltage synchronous channel operates from
the VIN2 pin. The VIN2 pin can be connected to either an
independent voltage supply or the high voltage channel
output for a two-stage power regulator.
In either configuration, if the high voltage channel is over-
loadedandpulledoutofregulation,thelowvoltagechannel
will be disabled. The SS2 pin will be discharged as well.
The minimum VIN2 voltage to regulate output voltage is:
V
DC
IN MIN
OUT
MAX
2
(
) ≈
Where DCMAX is the maximum duty cycle (refer to
the Switching Frequency section). If VIN2 is below the
calculated minimum voltage, the output will fall out of
regulation.
The maximum VIN2 for fixed frequency operation is:
V
DC
IN MAX
OUT
MIN
2
(
) ≈
WhereDCMINistheminimumdutycycle (refertotheSwitch-
ing Frequency section). For voltage that exceeds VIN2(MAX)
(up to 5.5V), the low voltage channel exhi-bits pulse-skip-
ping behavior, and the output ripple will increase.
Inductor Selection
Inductorselectioninvolvesinductance,saturationcurrent,
series resistance (DCR) and magnetic loss.
The inductance for the high voltage channel is:
L
V
f
OUT
D
S
1 1 7
1
=
+
.
where VOUT1 is high voltage channel output voltage, VD
is the forward voltage drop of the catch diode, and fS is
the switching frequency. For example, 3.3H is a reason-
able inductance for a 3.3V output with 2MHz switching
frequency.
Oncetheinductanceisselected,theinductorcurrentripple
and peak current can be calculated:
I
V
I
f
V
L
OUT
D
L
S
OUT
D
IN
1
=
+
(
)
–
I
L PEAK
OUT MAX
L
(
)
(
)
=
+
2
Figure 2. VIN Overvoltage Lockout
applicaTions inForMaTion
200ns/DIV
SW1
10V/DIV
IL1
0.5A/DIV
3640 F01
VIN = 30V
VOUT1 = 3.3V/0.2A
RT SET = 2MHz
10s/DIV
VIN
20V/DIV
55VPK, 40V, 15V
IL1
2A/DIV
3640 F02
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| LT3640IUFD#TRPBF | 3.4 A DUAL SWITCHING CONTROLLER, 2350 kHz SWITCHING FREQ-MAX, PQCC28 |
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