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LT1777IS#PBF

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1
LT1777
Low Noise Step-Down
Switching Regulator
■
Programmable dI/dt Limit
■
Internally Limited dV/dt
■
High Input Voltage: 48V Max
■
700mA Peak Switch Rating
■
True Current Mode Control
■
100kHz Fixed Operating Frequency
■
Synchronizable to 250kHz
■
Low Supply Current in Shutdown: 30µA
■
Low Thermal Resistance 16-Pin SO Package
The LT
®
1777 is a Buck (step-down) regulator designed for
noise sensitive applications. It contains a dI/dt limiting
circuit programmed via a small external inductor in the
switching path. Internal circuitry also generates controlled
dV/dt ramp rates.
The monolithic die includes all oscillator, control and
protection circuitry. The part can accept operating input
voltages as high as 48V, and contains an output switch
rated at 700mA peak current. Current mode control offers
excellent dynamic input supply rejection and short-circuit
protection. The internal control circuitry is normally pow-
ered via the V
CC
pin, thereby minimizing power drawn
directly from the V
IN
supply (see Applications Informa-
tion). The fused-lead SO16 package and 100kHz switch-
ing frequency allow for minimal PC board area
requirements.
V
SW
VOLTAGE
10V/DIV
500ns/DIV
1777 TA02
V
SW
Switching WaveformsLow Noise 5V Step-Down Supply
■
Automotive Cellular and GPS Receivers
■
Telecom Power Supplies
■
Industrial Instrument Power Supplies
V
SW
CURRENT
200mA/DIV
+
V
IN
V
CC
V
SW
LT1777
V
D
SHDN
SYNC
4
10
7
6
1µH*
220µH
100µF
10V
36.5k
1%
1777 TA01
V
OUT
5V
400mA
12.1k
1%
5
3
V
IN
24V
12
14
13
V
C
MBRS1100
FB
SGND
+
39µF
63V
12k
2200pF
100pF
*PROGRAMS dI/dT
100pF
, LTC and LT are registered trademarks of Linear Technology Corporation.
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
2
LT1777
ABSOLUTE MAXIMUM RATINGS
W
WW
U
WU
U
PACKAGE
/
O
RDER I FOR ATIO
(Note 1)
Supply Voltage ....................................................... 48V
Switch Voltage (V
IN
– V
SW
) (Note 4) ...................... 51V
SHDN, SYNC Pin Voltage.......................................... 7V
V
CC
Pin Voltage ...................................................... 30V
FB Pin Voltage ........................................................ 3.0V
Operating Junction Temperature Range
LT1777C............................................... 0°C to 125°C
LT1777I ........................................... –40°C to 125°C
Storage Temperature Range ................ –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
TOP VIEW
S PACKAGE
16-LEAD PLASTIC SO
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
GND*
NC
SHDN
V
CC
V
D
V
SW
SGND
GND*
GND*
NC
V
C
FB
SYNC
NC
V
IN
GND*
T
JMAX
= 125°C, θ
JA
= 50°C/W*
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at T
J
= 25°C.
V
IN
= 24V, V
SW
Open, V
CC
= 5V, V
C
= 1.4V unless otherwise noted.
ORDER PART
NUMBER
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Power Supplies
V
IN(MIN)
Minimum Input Voltage 6.7 7.0 V
● 7.4 V
I
VIN
V
IN
Supply Current V
C
= 0V 620 800 µA
● 900 µA
I
VCC
V
CC
Supply Current V
C
= 0V 2.5 3.5 mA
● 4.5 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 ∆I
C
= ±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
≤ 48V ● 0.01 %/V
Voltage Gain 200 600 V/V
*FOUR CORNER PINS ARE
FUSED TO INTERNAL DIE
ATTACH PADDLE FOR HEAT
SINKING. CONNECT THESE
FOUR PINS TO EXPANDED PC
LANDS FOR PROPER HEAT
SINKING.
LT1777CS
LT1777IS
3
LT1777
ELECTRICAL CHARACTERISTICS
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 dI/dt rate will cause a somewhat higher current limit in actual
application.
Note 4: During normal operation the V
SW
pin may fly as much as 3V
below ground. However, the LT1777 may not be used in an inverting
DC/DC configuration.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Output Switch
R
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
Output dl/dt Sense Voltage 1.3 V
● 0.6 2.0 V
Current Amplifier
Control Pin Threshold Duty Cycle = 0% 0.9 1.1 1.25 V
Control Voltage to Switch Transconductance 2 A/V
Timing
f Switching Frequency 90 100 110 kHz
● 85 115 kHz
Maximum Switch Duty Cycle ● 85 90 %
Sync Function
Minimum Sync Amplitude ● 1.5 2.2 V
Synchronization Range ● 130 250 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
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at T
J
= 25°C.
V
IN
= 24V, V
SW
Open, V
CC
= 5V, V
C
= 1.4V unless otherwise noted.
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LT1777IS#PBF

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Buy LT1777IS#PBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators L N Buck Sw Reg
Lifecycle:
New from this manufacturer.
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