LT1676 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LT1676' PDF : 16 Pages View PDF
LT1676
TYPICAL APPLICATIONS
VIN
12V TO
48V
+ C1
39µF
63V
5
1
VIN
2
SHDN VCC
3
VSW
C5
100pF
LT1676
6 SYNC
7
FB
8
VC
GND
4
D1
L1 +
MBRS1100 220µH
C3
2200pF
X7R
R3
22k
5%
C4
100pF
C1: PANASONIC HFQ
C2: AVX D CASE TPSD107M010R0080
C4, C5: X7R OR COG/NPO
D1: MOTOROLA 100V, 1A, SMD SCHOTTKY
L1: COILCRAFT DO3316P-224
FOR 3.3V VOUT VERSION:
R1: 24.3K, R2: 14.7k
L1: 150µH, DO3316P-154
IOUT: 0mA TO 500mA
C2
100µF
10V
VOUT
5V
R1 0mA to 500mA
36.5k
1%
R2
12.1k
1%
1676 F04a
Figure 4a. Minimum Component Count Application
90
80
70
60
50
VIN = 12V
40
VIN = 24V
30 VIN = 36V
VIN = 48V
20
1
10
100
ILOAD (mA)
1000
1676 F04b
Figure 4b. POUT/PIN Efficiency
VIN
+
R4
C1
5
210k
1%
1
VIN
2
SHDN VCC
3
VSW
R5
6.19k
1%
C5
LT1676
6
SYNC
7
FB
8
VC
C3
GND
R3
4
L1
+
VOUT
D1
C2 R1
R2
C4
1676 F05
Figure 5. User Programmable Undervoltage Lockout
desired VIN UVLO voltage minus 1.25V applied across it.
(The 2.5µA factor is an allowance to minimize error due to
SHDN pin input current.)
Behavior is as follows: Normal operation is observed at the
nominal input voltage of 48V. As the input voltage is
decreased to roughly 43V, switching action will stop, VOUT
will drop to zero, and the LT1676 will draw its VIN and VCC
quiescent currents from the VIN supply. At a much lower
input voltage, typically 18V or so at 25°C, the voltage on
the SHDN pin will drop to the shutdown threshold, and the
part will draw its shutdown current only from the VIN rail.
The resistive divider of R4 and R5 will continue to draw
power from VIN. (The user should be aware that while the
SHDN pin lockout threshold is relatively accurate includ-
ing temperature effects, the SHDN pin shutdown thresh-
old is more coarse, and exhibits considerably more
temperature drift. Nevertheless the shutdown threshold
will always be well below the lockout threshold.)
12
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