LT1676 Linear Technology, LT1676 Datasheet - Page 14

• Manufacturer Part Number: LT1676
• Description: Wide Input Range/ High Efficiency/ Step-Down Switching Regulator
• Manufacturer: Linear Technology

LT1676
to maintain proper short-circuit protection. Transistors
Q1, Q2 and resistor R7 form a high V
current voltage regulator to power U2.
Burst Mode Operation Configuration with UVLO
Figure 7a uses an external comparator to control the
LT1676 via its SHDN pin. As such, the user’s ability to set
an undervoltage lockout (UVLO) threshold with a resistor
divider from V
is regained in the slightly more complicated circuit shown
in Figure 8.
A dual comparator, the LTC1442, replaces the previous
single comparator. The second comparator monitors a
resistive divider between V
(user-adjustable) UVLO function. The two comparator
outputs are logically combined in a CMOS NOR gate (U3)
to drive the LT1676 SHDN pin.
TYPICAL APPLICATIONS
14
C1: PANASONIC HFQ 39 F AT 63V
C2: AVX D CASE 100 F 10V
D1: MOTOROLA 100V, 1A,
L1: COILCRAFT DO3316-224
TPSD107M010R0080
SMD SCHOTTKY
MBRS1100 (T3)
NC
Q2
2N2369
R7
10M
IN
Q1
PN2484
+
to SHDN pin to ground is lost. This ability
C1
6
1
8
Figure 7. Burst Mode Operation Configuration for High Efficiency at Light Load
SYNC
SHDN
OUT
V
LTC1440
IN
LT1676
–
2
GND
V
V
U1
V
U2
IN
IN
and ground to provide the
+
5
4
7
HYST
GND
V
V
REF
IN
IN
SW
CC
FB
V
1
C
+
–
U
(a)
2
3
7
8
3
4
6
5
IN
, low quiescent
C3
100pF
R5
22k
R6
2.4M
D1
L1
+
C2
Minimum Size Inductor Application
Figure 4a employs power path parts that are capable of
delivering the full rated output capability of the LT1676.
Potential users with low output current requirements may
be interested in substituting a physically smaller and less
costly power inductor. The circuit shown on the last page
of this data sheet is topologically identical to the basic
application, but specifies a much smaller inductor, and, a
somewhat smaller input electrolytic capacitor. This circuit
is capable of delivering up to 150mA at 5V, or, up to 200mA
at 3.3V. The only disadvantage is that due to the increased
resistance in the inductor, the circuit is no longer capable
of withstanding indefinite short circuits to ground. The
LT1676 will still current limit at its nominal I
this will overheat the inductor. Momentary short circuits
of a few seconds or less can still be tolerated.
R1
39k
5%
R2
10k
5%
R3
323k
1%
R4
100k
1%
1676 F07a
V
5V
OUT
90
80
70
60
50
40
30
20
1
V
IN
V
= 12V
IN
= 24V
V
IN
V
IN
= 36V
= 48V
10
I
LOAD
(b)
(mA)
LIM
100
value, but
1676 F07b
1000