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LT1776IS8#TRPBF

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1
LT1776
Wide Input Range,
High Efficiency, Step-Down
Switching Regulator
FEATURES
DESCRIPTION
U
The LT
®
1776 is a wide input range, high efficiency Buck
(step-down) switching regulator. The monolithic die in-
cludes all oscillator, control and protection circuitry. The
part can accept input voltages as high as 60V and contains
an output switch rated at 700mA peak current. Current
mode control delivers excellent dynamic input supply
rejection and short-circuit protection.
The LT1776 contains several features to enhance effi-
ciency. The internal control circuitry is normally powered
via the V
CC
pin, thereby minimizing power drawn directly
from the V
IN
supply (see Applications Information). The
action of the LT1776 switch circuitry is also load depen-
dent. At medium to high loads, the output switch circuitry
maintains fast rise time for good efficiency. At light loads,
rise time is deliberately reduced to avoid pulse skipping
behavior.
The available SO-8 package and 200kHz switching fre-
quency allow for minimal PC board area requirements.
TYPICAL APPLICATION
U
■
Wide Input Range: 7.4V to 40V
■
Tolerates Input Transients to 60V
■
700mA Peak Switch Rating
■
Adaptive Switch Drive Maintains Efficiency at High
Load Without Pulse Skipping at Light Load
■
True Current Mode Control
■
200kHz Fixed Operating Frequency
■
Synchronizable to 400kHz
■
Low Supply Current in Shutdown: 30µA
■
Available in 8-Pin SO and PDIP Packages
39µF
63V
1776 F01
V
IN
V
CC
V
SW
LT1776
FB
V
C
SHDN
SYNC
2
5
4
3
7
8
1
6
GND
+
100µF
10V
+
MBR160
36.5k
1%
5V
400mA
12.1k
1%
22k
100µH*
2200pF
V
IN
8V TO 40V
100pF
*43T #30 ON MAGNETICS
MPP #55030
Efficiency vs V
IN
and I
LOAD
LOAD CURRENT
(mA)
1
60
EFFICIENCY (%)
70
80
90
10 100 1000
1776 TA01
50
40
30
20
V
IN
= 10V
V
IN
= 20V
V
IN
= 30V
V
IN
= 40V
Figure 1
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIONS
U
■
Automotive DC/DC Converters
■
Cellular Phone Battery Charger Accessories
■
IEEE 1394 Step-Down Converters
2
LT1776
ABSOLUTE MAXIMUM RATINGS
W
WW
U
(Note 1)
Supply Voltage (Note 5) .......................................... 60V
Switch Voltage (Note 5)........................................... 60V
SHDN, SYNC Pin Voltage........................................... 7V
V
CC
Pin Voltage ....................................................... 30V
FB Pin Voltage ........................................................... 3V
Operating Junction Temperature Range
LT1776C................................................ 0°C to 125°C
LT1776I ............................................ –40°C to 125°C
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec)..................300°C
PACKAGE/ORDER INFORMATION
W
U
U
ORDER PART
NUMBER
LT1776CN8
LT1776CS8
LT1776IN8
LT1776IS8
S8 PART MARKING
1776
1776I
Consult factory for Military grade parts.
V
IN
= 40V, V
SW
open, V
CC
= 5V, V
C
= 1.4V unless otherwise noted.
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C.
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Power Supplies
V
IN(MIN)
Minimum Input Voltage 6.7 7.0 V
● 7.4 V
Thermally Limited Continuous Operating Voltage ● 40 V
I
VIN
V
IN
Supply Current V
C
= 0V 620 800 µA
● 900 µA
I
VCC
V
CC
Supply Current V
C
= 0V 3.2 4.0 mA
● 5.0 mA
V
VCC
V
CC
Dropout Voltage (Note 2) 2.8 3.1 V
Shutdown Mode I
VIN
V
SHDN
= 0V 30 50 µA
● 75 µA
Feedback Amplifier
V
REF
Reference Voltage 1.225 1.240 1.255 V
● 1.215 1.265 V
I
IN
FB Pin Input Bias Current 600 1500 nA
g
m
Feedback Amplifier Transconductance ∆lc = ±10µA 400 650 1000 µmho
● 200 1500 µmho
I
SRC
, I
SNK
Feedback Amplifier Source or Sink Current 60 100 170 µA
● 45 220 µA
V
CL
Feedback Amplifier Clamp Voltage 2.0 V
Reference Voltage Line Regulation 12V ≤ V
IN
≤ 60V ● 0.01 %/V
Voltage Gain 200 600 V/V
Output Switch
V
ON
Output Switch On Voltage I
SW
= 0.5A 1.0 1.5 V
I
LIM
Switch Current Limit (Note 3) ● 0.55 0.70 1.0 A
Current Amplifier
Control Pin Threshold Duty Cycle = 0% 0.9 1.1 1.25 V
Control Voltage to Switch Transconductance 2 A/V
T
JMAX
= 125°C, θ
JA
= 130°C/ W (N8)
T
JMAX
= 125°C, θ
JA
= 110°C/ W (S8)
1
2
3
4
8
7
6
5
TOP VIEW
V
C
FB
SYNC
V
IN
SHDN
V
CC
V
SW
GND
N8 PACKAGE
8-LEAD PDIP
S8 PACKAGE
8-LEAD PLASTIC SO
3
LT1776
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C.
V
IN
= 40V, V
SW
open, V
CC
= 5V, V
C
= 1.4V unless otherwise noted.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Timing
f Switching Frequency 180 200 220 kHz
● 170 230 kHz
Maximum Switch Duty Cycle ● 85 90 %
t
ON(MIN)
Minimum Switch On Time High dV/dt Mode, R
L
= 39Ω (Note 4) 300 ns
Boost Operation
V
C
Pin Boost Threshold 1.35 V
dV/dt Below Threshold 0.2 V/ns
dV/dt Above Threshold 1.6 V/ns
Sync Function
Minimum Sync Amplitude ● 1.5 2.2 V
Synchronization Range (Note 6) ● 250 400 kHz
SYNC Pin Input R 40 kΩ
SHDN Pin Function
V
SHDN
Shutdown Mode Threshold 0.5 V
● 0.2 0.8 V
Upper Lockout Threshold Switching Action On 1.260 V
Lower Lockout Threshold Switching Action Off 1.245 V
I
SHDN
Shutdown Pin Current V
SHDN
= 0V 12 20 µA
V
SHDN
= 1.25V 2.5 10 µA
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: Control circuitry powered from V
CC
.
Note 3: Switch current limit is DC trimmed and tested in production.
Inductor dl/dt rate will cause a somewhat higher current limit in actual
application.
Note 4: Minimum switch on time is production tested with a 39Ω resistive
load to ground.
Note 5: Parts are guaranteed to survive 60V on V
IN
and V
SW
. However,
thermal constraints will limit V
IN
in some applications, depending primarily
on maximum output current and switching frequency. See Applications
section for more information.
Note 6: Internal oscillator is guaranteed to sync up to 400kHz. However,
thermal constraints and/or controllability issues may place a lower limit on
switching frequency in actual usage. See Applications section for more
information.
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LT1776IS8#TRPBF

Mfr. #:
Buy LT1776IS8#TRPBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators Wide In Rng, Hi Eff, Buck Sw Reg
Lifecycle:
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