LT1766/LT1766-5
5.5V to 60V 1.5A, 200kHz
Step-Down Switching Regulator
FEATURES
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DESCRIPTIO
Wide Input Range: 5.5V to 60V
1.5A Peak Switch Current
Constant 200kHz Switching Frequency
Saturating Switch Design: 0.2Ω
Peak Switch Current Rating Maintained Over
Full Duty Cycle Range
Low Effective Supply Current: 2.5mA
Low Shutdown Current: 25µA
1.2V Feedback Reference Voltage (LT1766)
5V Fixed Output (LT1766-5)
Easily Synchronizable
Cycle-by-Cycle Current Limiting
Small 16-Pin SSOP and Thermally Enhanced
TSSOP Packages
The LT
®
1766/LT1766-5 are 200kHz monolithic buck
switching regulators that accept input voltages up to 60V.
A high efficiency 1.5A, 0.2Ω switch is included on the die
along with all the necessary oscillator, control and logic cir-
cuitry. A current mode control architecture delivers fast
transient response and excellent loop stability.
Special design techniques and a new high voltage process
achieve high efficiency over a wide input range. Efficiency
is maintained over a wide output current range by using the
output to bias the circuitry and by utilizing a supply boost
capacitor to saturate the power switch. Patented circuitry*
maintains peak switch current over the full duty cycle range.
A shutdown pin reduces supply current to 25µA and the
device can be externally synchronized from 228kHz to
700kHz with logic level inputs.
The LT1766/LT1766-5 are available in a 16-pin fused-lead
SSOP package or a TSSOP package with exposed backside
for improved thermal performance.
, LTC and LT are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners. *Protected by U.S. Patents
including 6498466, 6531909
APPLICATIO S
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High Voltage, Industrial and Automotive
Portable Computers
Battery-Powered Systems
Battery Chargers
Distributed Power Systems
TYPICAL APPLICATIO
6
V
IN
5.5V*
TO 60V
BOOST
4
2.2µF
†
100V
CERAMIC
OFF ON
15
14
V
IN
LT1766
SHDN
SYNC
GND
1, 8, 9, 16
2.2k
0.022µF
5V Buck Converter
1N4148W
0.33µF
SW
2
47µH
10MQ060N
V
OUT
5V
1A
+
BIAS
FB
V
C
11
220pF
10
12
15.4k
4.99k
100µF 10V
SOLID
TANTALUM
EFFICIENCY (%)
1766 TA01
*FOR INPUT VOLTAGES BELOW 7.5V, SOME RESTRICTIONS MAY APPLY
†
TDK C4532X7R2A225K
U
Efficiency vs Load Current
100
V
OUT
= 5V
L = 47µH
V
IN
= 12V
90
V
IN
= 42V
80
70
60
50
0
0.25
0.75
1.00
0.50
LOAD CURRENT (A)
1.25
1766 TA02
U
U
1766fb
1
LT1766/LT1766-5
ABSOLUTE
(Note 1)
AXI U
RATI GS
Operating Junction Temperature Range
LT1766EFE/LT1766EFE-5/LT1766EGN/
LT1766EGN-5 (Note 8,10) ................. – 40°C to 125°C
LT1766IFE/LT1766IFE-5/
LT1766IGN/LT1766IGN-5 (Note 8,10) – 40°C to 125°C
LT1766HGN/LT1766HFE ................... – 40°C to 140°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
Input Voltage (V
IN
) ................................................. 60V
BOOST Pin Above SW ............................................ 35V
BOOST Pin Voltage ................................................. 68V
SYNC, SENSE Voltage (LT1766-5) ........................... 7V
SHDN Voltage ........................................................... 6V
BIAS Pin Voltage .................................................... 30V
FB Pin Voltage/Current (LT1766) ................... 3.5V/2mA
PACKAGE/ORDER I FOR ATIO
TOP VIEW
GND
SW
NC
V
IN
NC
BOOST
NC
GND
1
2
3
4
5
6
7
8
17
16 GND
15 SHDN
14 SYNC
13 NC
12 FB/SENSE
11 V
C
10 BIAS
9
GND
FE PACKAGE
16-LEAD PLASTIC TSSOP
θ
JA
= 45°C/W,
θ
JC
(PAD) = 10°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE CONNECTED TO PCB
ORDER PART NUMBER
LT1766EFE
LT1766IFE
LT1766HFE
LT1766EFE-5
LT1766IFE-5
FE PART MARKING
1766EFE
1766IFE
1766HFE
1766EFE-5
1766IFE-5
Order Options
Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER
Reference Voltage (V
REF
) (LT1766)
SENSE Voltage (LT1766-5)
SENSE Pin Resistance (LT1766-5)
FB Input Bias Current (LT1766)
(LT1766E/LT1766I GRADE)
The
●
denotes specifications which apply over the full operating temperature range, otherwise specifications are at T
J
= 25°C.
V
IN
= 15V, V
C
= 1.5V, SHDN = 1V, BOOST open circuit, SW open circuit, unless otherwise noted.
CONDITIONS
5.5V
≤
V
IN
≤
60V
V
OL
+ 0.2
≤
V
C
≤
V
OH
– 0.2
5.5V
≤
V
IN
≤
60V
V
OL
+ 0.2V
≤
V
C
≤
V
OH
– 0.2V
●
●
●
2
U
U
W
W W
U
W
TOP VIEW
GND
SW
NC
V
IN
NC
BOOST
NC
GND
1
2
3
4
5
6
7
8
16 GND
15 SHDN
14 SYNC
13 NC
12 FB/SENSE
11 V
C
10 BIAS
9
GND
GN PACKAGE
16-LEAD PLASTIC SSOP
θ
JA
= 85°C/W,
θ
JC
(PIN 8) = 25°C/W
FOUR CORNER PINS SOLDERED TO GROUND PLANE
ORDER PART NUMBER
LT1766EGN
LT1766IGN
LT1766HGN
LT1766EGN-5
LT1766IGN-5
GN PART MARKING
1766
1766I
1766H
17665
1766I5
MIN
1.204
1.195
4.94
4.90
9.5
TYP
1.219
5
13.8
–0.5
MAX
1.234
1.243
5.06
5.10
19
–1.5
UNITS
V
V
V
V
kΩ
µA
1766fb
LT1766/LT1766-5
ELECTRICAL CHARACTERISTICS
PARAMETER
Error Amp Voltage Gain
Error Amp g
m
V
C
to Switch g
m
EA Source Current
EA Sink Current
V
C
Switching Threshold
V
C
High Clamp
Switch Current Limit
Switch On Resistance
Maximum Switch Duty Cycle
Switch Frequency
f
SW
Line Regulation
f
SW
Frequency Shifting Threshold
Minimum Input Voltage
Minimum Boost Voltage
Boost Current (Note 5)
Input Supply Current (I
VIN
)
Bias Supply Current (I
BIAS
)
Shutdown Supply Current
Lockout Threshold
Shutdown Thresholds
Minimum SYNC Amplitude
SYNC Frequency Range
SYNC Input Resistance
(LT1766E/LT1766I GRADE)
The
●
denotes specifications which apply over the full operating temperature range, otherwise specifications are at T
J
= 25°C.
V
IN
= 15V, V
C
= 1.5V, SHDN = 1V, BOOST open circuit, SW open circuit, unless otherwise noted.
CONDITIONS
(Notes 2, 9)
dl (V
C
) =
±10µA
(Note 9)
MIN
200
1500
1000
125
100
TYP
400
2000
1.7
FB = 1V or V
SENSE
= 4.1V
FB = 1.4V or V
SENSE
= 5.7V
Duty Cycle = 0
SHDN = 1V
V
C
Open, Boost = V
IN
+ 5V, FB = 1V or V
SENSE
= 4.1V
I
SW
= 1.5A, Boost = V
IN
+ 5V (Note 7)
FB = 1V or V
SENSE
= 4.1V
V
C
Set to Give DC = 50%
5.5V
≤
V
IN
≤
60V
Df = 10kHz
(Note 3)
(Note 4) I
SW
≤
1.5A
Boost = V
IN
+ 5V, I
SW
= 0.5A
Boost = V
IN
+ 5V, I
SW
= 1.5A
(Note 6) V
BIAS
= 5V
(Note 6) V
BIAS
= 5V
SHDN = 0V, V
IN
≤
60V, SW = 0V, V
C
Open
V
C
Open
V
C
Open, Shutting Down
V
C
Open, Starting Up
●
●
●
●
●
●
●
●
●
●
●
MAX
3000
4200
400
450
UNITS
V/V
µMho
µMho
A/V
µA
µA
V
V
●
225
225
0.9
2.1
1.5
2
0.2
96
200
200
0.05
0.8
4.6
1.8
12
45
1.4
2.9
25
3
0.3
0.4
93
90
184
172
216
228
0.15
5.5
3
25
70
2.2
4.2
75
200
2.53
0.6
0.6
2.2
700
A
Ω
Ω
%
%
kHz
kHz
%/V
V
V
V
mA
mA
mA
mA
µA
µA
V
V
V
V
kHz
kΩ
●
●
●
●
●
2.3
0.15
0.25
228
2.42
0.37
0.45
1.5
20
(LT1766H GRADE)
The
●
denotes specifications which apply over the full operating temperature range, otherwise specifications are at T
J
= 25°C.
V
IN
= 15V, V
C
= 1.5V, SHDN = 1V, BOOST open circuit, SW open circuit, unless otherwise noted.
PARAMETER
Reference Voltage (V
REF
)
FB Input Bias Current
Error Amp Voltage Gain
Error Amp g
m
V
C
to Switch g
m
EA Source Current
EA Sink Current
FB = 1V or V
SENSE
= 4.1V
FB = 1.4V or V
SENSE
= 5.7V
●
●
CONDITIONS
5.5V
≤
V
IN
≤
60V
V
OL
+ 0.2
≤
V
C
≤
V
OH
– 0.2
(Notes 2, 9)
dl (V
C
) =
±10µA
(Note 9)
●
●
●
MIN
1.204
1.175
200
1500
900
125
100
TYP
1.219
–0.5
400
2000
1.7
225
225
MAX
1.234
1.265
–1.5
3000
4200
400
450
UNITS
V
V
µA
V/V
µMho
µMho
A/V
µA
µA
1766fb
3
LT1766/LT1766-5
ELECTRICAL CHARACTERISTICS
PARAMETER
V
C
Switching Threshold
V
C
High Clamp
Switch Current Limit
Switch On Resistance
Maximum Switch Duty Cycle
Switch Frequency
f
SW
Line Regulation
f
SW
Frequency Shifting Threshold
Minimum Input Voltage
Minimum Boost Voltage
Boost Current (Note 5)
Input Supply Current (I
VIN
)
Bias Supply Current (I
BIAS
)
Shutdown Supply Current
Lockout Threshold
Shutdown Thresholds
Minimum SYNC Amplitude
SYNC Frequency Range
SYNC Input Resistance
(LT1766H GRADE)
The
●
denotes specifications which apply over the full operating temperature range, otherwise specifications are at T
J
= 25°C.
V
IN
= 15V, V
C
= 1.5V, SHDN = 1V, BOOST open circuit, SW open circuit, unless otherwise noted.
CONDITIONS
Duty Cycle = 0
SHDN = 1V
V
C
Open, Boost = V
IN
+ 5V, FB = 1V or V
SENSE
= 4.1V
I
SW
= 0.75A, Boost = V
IN
+ 5V (Note 7)
●
●
MIN
TYP
0.9
2.1
MAX
UNITS
V
V
0.75
2
0.2
3
0.3
0.8
A
Ω
Ω
%
%
FB = 1V or V
SENSE
= 4.1V
●
93
90
184
135
96
200
200
0.05
0.8
4.6
1.8
12
45
1.4
2.9
25
216
228
0.15
5.5
3
40
100
2.2
4.2
120
500
2.68
0.9
0.9
2.2
700
20
V
C
Set to Give DC = 50%
●
kHz
kHz
%/V
V
V
V
mA
mA
mA
mA
µA
µA
V
V
V
V
kHz
kΩ
5.5V
≤
V
IN
≤
60V
Df = 10kHz
(Note 3)
(Note 4) I
SW
≤
0.75A
Boost = V
IN
+ 5V, I
SW
= 0.5A
Boost = V
IN
+ 5V, I
SW
= 0.75A
(Note 6) V
BIAS
= 5V
(Note 6) V
BIAS
= 5V
SHDN = 0V, V
IN
≤
60V, SW = 0V, V
C
Open
●
●
●
●
●
●
V
C
Open
V
C
Open, Shutting Down
V
C
Open, Starting Up
●
●
●
●
2.3
0.15
0.25
228
2.42
0.37
0.45
1.5
Note 1:
Absolute Maximum Ratings are those values beyond which the life of a
device may be impaired.
Note 2:
Gain is measured with a V
C
swing equal to 200mV above the low clamp
level to 200mV below the upper clamp level.
Note 3:
Minimum input voltage is not measured directly, but is guaranteed by
other tests. It is defined as the voltage where internal bias lines are still regulated
so that the reference voltage and oscillator remain constant. Actual minimum
input voltage to maintain a regulated output will depend upon output voltage and
load current. See Applications Information.
Note 4:
This is the minimum voltage across the boost capacitor needed to
guarantee full saturation of the internal power switch.
Note 5:
Boost current is the current flowing into the BOOST pin with the pin held
5V above input voltage. It flows only during switch on time.
Note 6:
Input supply current is the quiescent current drawn by the input pin when
the BIAS pin is held at 5V with switching disabled. Bias supply current is the
current drawn by the BIAS pin when the BIAS pin is held at 5V. Total input
referred supply current is calculated by summing input supply current (I
VIN
) with
a fraction of bias supply current (I
BIAS
):
I
TOTAL
= I
VIN
+ (I
BIAS
)(V
OUT
/V
IN
)
With V
IN
= 15V, V
OUT
= 5V, I
VIN
= 1.4mA, I
BIAS
= 2.9mA, I
TOTAL
= 2.4mA.
Note 7:
Switch on resistance is calculated by dividing V
IN
to SW voltage by the
forced current. See Typical Performance Characteristics for the graph of switch
voltage at other currents.
Note 8:
The LT1766EGN, LT1766EGN-5, LT1766EFE and LT1766EFE-5 are
guaranteed to meet performance specifications from 0°C to 125°C junction
temperature. Specifications over the –40°C to 125°C operating junction
temperature range are assured by design, characterization and correlation with
statistical process controls. The LT1766IGN, LT1766IGN-5, LT1766IFE and
LT1766IFE-5 are guaranteed over the full
–40°C to 125°C operating junction temperature range. The LT1766HGN and
LT1766HFE are guaranteed over the full –40°C to 140°C operating junction
temperature range.
Note 9:
Transconductance and voltage gain refer to the internal amplifier exclusive
of the voltage divider. To calculate gain and transconductance, refer to the SENSE
pin on fixed voltage parts. Divide the values shown by the ratio V
OUT
/1.219.
Note 10:
This IC includes overtemperature protection that is intended to protect
the device during momentary overload conditions. Junction temperature will
exceed 140°C when overtemperature protection is active. Continuous operation
above the specified maximum operating junction temperature may impair device
reliability.
Note 11:
High junction temperatures degrade operating lifetimes. Operating
lifetime at junction temperatures between 125°C and 140°C is derated to 1000
hours.
1766fb
4
LT1766/LT1766-5
TYPICAL PERFOR A CE CHARACTERISTICS
Switch Peak Current Limit
2.5
T
A
= 25°C
1.234
1.229
SWITCH PEAK CURRENT (A)
TYPICAL
2.0
FEEDBACK VOLTAGE (V)
VOLTAGE
1.219
CURRENT
1.214
0.5
1.209
1.0
CURRENT (µA)
1.5
GUARANTEED MINIMUM
1.0
0
20
40
60
DUTY CYCLE (%)
80
100
1766 G01
Lockout and Shutdown
Thresholds
2.4
INPUT SUPPLY CURRENT (µA)
INPUT SUPPLY CURRENT (µA)
2.0
LOCKOUT
SHDN PIN VOLTAGE (V)
1.6
1.2
0.8
START-UP
0.4
SHUTDOWN
0
25 50 75 100 125 150
–50 –25 0
JUNCTION TEMPERATURE (°C)
1766 G04
Error Amplifier Transconductance
2500
TRANSCONDUCTANCE (µmho)
2000
GAIN (µMho)
2500
GAIN
150
PHASE (DEG)
SWITICHING FREQUENCY (kHz)
OR FB CURRENT (µA)
1500
1000
500
0
–50 –25
0
25
50
75
JUNCTION TEMPERATURE (°C)
1766 G07
U W
FB Pin Voltage and Current
2.0
250
200
1.5
1.224
150
100
12
6
0
25 50 75 100 125 150
0
JUNCTION TEMPERATURE (°C)
1766 G02
SHDN Pin Bias Current
CURRENT REQUIRED TO FORCE SHUTDOWN
(FLOWS OUT OF PIN). AFTER SHUTDOWN,
CURRENT DROPS TO A FEW
µA
CURRENT (µA)
AT 2.38V STANDBY THRESHOLD
(CURRENT FLOWS OUT OF PIN)
1.204
–50 –25
0
–50 –25 0
25 50 75 100 125 150
JUNCTION TEMPERATURE (°C)
1766 G03
Shutdown Supply Current
40
300
250
V
SHDN
= 0V
35 T
A
= 25°C
30
25
20
15
10
5
0
0
10
20
30
40
INPUT VOLTAGE (V)
50
60
1766 G05
Shutdown Supply Current
T
A
= 25°C
V
IN
= 60V
200
V
IN
= 15V
150
100
50
0
0
0.1
0.2
0.3
0.4
SHUTDOWN VOLTAGE (V)
0.5
1766 G06
Error Amplifier Transconductance
3000
T
A
= 25°C
PHASE
200
Frequency Foldback
600
500
400
300
200
100
FB PIN
CURRENT
0
0
0.5
V
FB
(V)
1.0
1.5
1766 G09
T
A
= 25°C
2000
100
1500
V
FB
2 • 10
–3
(
)
R
OUT
200k
V
C
C
OUT
12pF
50
SWITCHING
FREQUENCY
1000
ERROR AMPLIFIER EQUIVALENT CIRCUIT
0
R
LOAD
= 50Ω
100 125 150
500
100
1k
10k
100k
FREQUENCY (Hz)
1M
–50
10M
1766 G08
1766fb
5
