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1
LT1766/LT1766-5
1766fa
BOOST
V
IN
6
2
10
12
10MQ060N
15.4k
V
OUT
5V
1A
4
15
14
11
220pF
0.022
F
*
FOR INPUT VOLTAGES BELOW 7.5V, SOME RESTRICTIONS MAY APPLY
TDK C4532X7R2A225K
1, 8, 9, 16
LT1766
SHDN
SYNC
SW
BIAS
FB
V
C
GND
0.33
F
100
F 10V
SOLID
TANTALUM
47
H
1N4148W
4.99k
1766 TA01
2.2
F
100V
CERAMIC
V
IN
5.5V*
TO 60V
+
2.2k
ON
OFF
5.5V to 60V 1.5A, 200kHz
Step-Down Switching Regulator
s
Wide Input Range: 5.5V to 60V
s
1.5A Peak Switch Current
s
Constant 200kHz Switching Frequency
s
Saturating Switch Design: 0.2
s
Peak Switch Current Rating Maintained Over
Full Duty Cycle Range
s
Low Effective Supply Current: 2.5mA
s
Low Shutdown Current: 25
A
s
1.2V Feedback Reference Voltage (LT1766)
s
5V Fixed Output (LT1766-5)
s
Easily Synchronizable
s
Cycle-by-Cycle Current Limiting
s
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, 0.2
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 25
A 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.
s
High Voltage, Industrial and Automotive
s
Portable Computers
s
Battery-Powered Systems
s
Battery Chargers
s
Distributed Power Systems
, LTC and LT are registered trademarks of Linear Technology Corporation.
5V Buck Converter
Efficiency vs Load Current
LOAD CURRENT (A)
0
EFFICIENCY (%)
80
90
100
1.00
1766 TA02
70
60
50
0.25
0.50
0.75
1.25
V
IN
= 12V
V
IN
= 42V
V
OUT
= 5V
L = 47
H
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
*Patent # 6, 498, 466
2
LT1766/LT1766-5
1766fa
(Note 1)
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
ORDER PART
NUMBER
LT1766EFE
LT1766IFE
LT1766EFE-5
LT1766IFE-5
T
JMAX
= 125
C,
JA
= 85
C/W,
JC
(PIN 8) = 25
C/W
FOUR CORNER PINS SOLDERED
TO GROUND PLANE
ABSOLUTE AXI U RATI GS
W
W
W
U
PACKAGE/ORDER I FOR ATIO
U
U
W
GN PACKAGE
16-LEAD PLASTIC SSOP
1
2
3
4
5
6
7
8
TOP VIEW
16
15
14
13
12
11
10
9
GND
SW
NC
V
IN
NC
BOOST
NC
GND
GND
SHDN
SYNC
NC
FB/SENSE
V
C
BIAS
GND
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
Storage Temperature Range ................ 65
C to 150
C
Lead Temperature (Soldering, 10 sec)................. 300
C
ORDER PART
NUMBER
LT1766EGN
LT1766IGN
LT1766EGN-5
LT1766IGN-5
GN PART MARKING
1766
1766I
17665
1766I5
FE PACKAGE
16-LEAD PLASTIC TSSOP
1
2
3
4
5
6
7
8
TOP VIEW
16
15
14
13
12
11
10
9
GND
SW
NC
V
IN
NC
BOOST
NC
GND
GND
SHDN
SYNC
NC
FB/SENSE
V
C
BIAS
GND
17
T
JMAX
= 125
C,
JA
= 45
C/W,
JC
(PAD) = 10
C/W
EXPOSED PAD (PIN 17) IS GND.
MUST BE SOLDERED TO PCB
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Reference Voltage (V
REF
) (LT1766)
5.5V
V
IN
60V
1.204
1.219
1.234
V
V
OL
+ 0.2
V
C
V
OH
0.2
q
1.195
1.243
V
SENSE Voltage (LT1766-5)
5.5V
V
IN
60V
4.94
5
5.06
V
V
OL
+ 0.2V
V
C
V
OH
0.2V
q
4.90
5.10
V
SENSE Pin Resistance (LT1766-5)
9.5
13.8
19
k
FB Input Bias Current (LT1766)
q
0.5
1.5
A
Error Amp Voltage Gain
(Notes 2, 9)
200
400
V/V
Error Amp g
m
dl (V
C
) =
10
A (Note 9)
1500
2000
3000
Mho
q
1000
4200
Mho
V
C
to Switch g
m
1.7
A/V
EA Source Current
FB = 1V or V
SENSE
= 4.1V
q
125
225
400
A
EA Sink Current
FB = 1.4V or V
SENSE
= 5.7V
q
100
225
450
A
V
C
Switching Threshold
Duty Cycle = 0
0.9
V
V
C
High Clamp
SHDN = 1V
2.1
V
The
q
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.
ELECTRICAL CHARACTERISTICS
Consult LTC Marketing for parts specified with wider operating temperature ranges.
3
LT1766/LT1766-5
1766fa
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Switch Current Limit
V
C
Open, Boost = V
IN
+ 5V, FB = 1V or V
SENSE
= 4.1V
q
1.5
2
3
A
Switch On Resistance
I
SW
= 1.5A, Boost = V
IN
+ 5V (Note 7)
0.2
0.3
q
0.4
Maximum Switch Duty Cycle
FB = 1V or V
SENSE
= 4.1V
93
96
%
q
90
%
Switch Frequency
V
C
Set to Give DC = 50%
184
200
216
kHz
q
172
200
228
kHz
f
SW
Line Regulation
5.5V
V
IN
60V
q
0.05
0.15
%/V
f
SW
Frequency Shifting Threshold
Df = 10kHz
0.8
V
Minimum Input Voltage
(Note 3)
q
4.6
5.5
V
Minimum Boost Voltage
(Note 4) I
SW
1.5A
q
1.8
3
V
Boost Current (Note 5)
Boost = V
IN
+ 5V, I
SW
= 0.5A
q
12
25
mA
Boost = V
IN
+ 5V, I
SW
= 1.5A
q
45
70
mA
Input Supply Current (I
VIN
)
(Note 6) V
BIAS
= 5V
1.4
2.2
mA
Bias Supply Current (I
BIAS
)
(Note 6) V
BIAS
= 5V
2.9
4.2
mA
Shutdown Supply Current
SHDN = 0V, V
IN
60V, SW = 0V, V
C
Open
25
75
A
q
200
A
Lockout Threshold
V
C
Open
q
2.3
2.42
2.53
V
Shutdown Thresholds
V
C
Open, Shutting Down
q
0.15
0.37
0.6
V
V
C
Open, Starting Up
q
0.25
0.45
0.6
V
Minimum SYNC Amplitude
q
1.5
2.2
V
SYNC Frequency Range
228
700
kHz
SYNC Input Resistance
20
k
The
q
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.
ELECTRICAL CHARACTERISTICS
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 (1.5A). 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.
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 125
C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
4
LT1766/LT1766-5
1766fa
Switch Peak Current Limit
SHDN Pin Bias Current
Shutdown Supply Current
Lockout and Shutdown
Thresholds
Shutdown Supply Current
Error Amplifier Transconductance
FB Pin Voltage and Current
Error Amplifier Transconductance
Frequency Foldback
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
DUTY CYCLE (%)
1.0
SWITCH PEAK CURRENT (A)
1.5
2.0
2.5
20
40
TYPICAL
60
80
1766 G01
100
0
GUARANTEED MINIMUM
T
A
= 25
C
JUNCTION TEMPERATURE (
C)
50
FEEDBACK VOLTAGE (V)
CURRENT (
A)
1.224
1.229
1.234
25
75
1766 G02
1.219
1.214
25
0
50
100
125
1.209
1.204
1.5
2.0
1.0
0.5
0
VOLTAGE
CURRENT
JUNCTION TEMPERATURE (
C)
50
250
200
150
100
12
6
0
25
75
1766 G03
25
0
50
100
125
CURRENT (
A)
CURRENT REQUIRED TO FORCE SHUTDOWN
(FLOWS OUT OF PIN). AFTER SHUTDOWN,
CURRENT DROPS TO A FEW
A
AT 2.38V STANDBY THRESHOLD
(CURRENT FLOWS OUT OF PIN)
JUNCTION TEMPERATURE (
C)
50
SHDN PIN VOLTAGE (V)
50
100
1766 G04
0
25
75
2.4
2.0
1.6
1.2
0.8
0.4
0
25
125
LOCKOUT
START-UP
SHUTDOWN
INPUT VOLTAGE (V)
0
INPUT SUPPLY CURRENT (
A)
1766 G05
10
20
30
40
50
60
40
35
30
25
20
15
10
5
0
V
SHDN
= 0V
T
A
= 25
C
SHUTDOWN VOLTAGE (V)
0
0
INPUT SUPPLY CURRENT (
A)
50
100
150
200
250
300
0.1
0.2
0.3
0.4
1766 G06
0.5
V
IN
= 60V
V
IN
= 15V
T
A
= 25
C
JUNCTION TEMPERATURE (
C)
TRANSCONDUCTANCE (
mho)
1766 G07
2500
2000
1500
1000
500
0
50
50
100
0
25
75
25
125
FREQUENCY (Hz)
GAIN (
Mho)
PHASE (DEG)
3000
2500
2000
1500
1000
500
200
150
100
50
0
50
100
10k
100k
10M
1766 G08
1k
1M
GAIN
PHASE
ERROR AMPLIFIER EQUIVALENT CIRCUIT
R
OUT
200k
C
OUT
12pF
V
C
R
LOAD
= 50
V
FB
2
10
3
)
(
T
A
= 25
C
V
FB
(V)
0
SWITICHING FREQUENCY (kHz)
OR FB CURRENT (
A)
300
400
600
500
1766 G09
200
100
0
0.5
1.0
1.5
SWITCHING
FREQUENCY
FB PIN
CURRENT
T
A
= 25
C
5
LT1766/LT1766-5
1766fa
Switching Frequency
BOOST Pin Current
V
C
Pin Shutdown Threshold
Minimum Input Voltage with 5V
Output
Switch Voltage Drop
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
JUNCTION TEMPERATURE (
C)
50
FREQUENCY (kHz)
50
100
1766 G10
0
25
75
230
220
210
200
190
180
170
25
125
LOAD CURRENT (A)
0
INPUT VOLTAGE (V)
1766 G11
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
1
7.5
7.0
6.5
6.0
5.5
5.0
MINIMUM INPUT
VOLTAGE TO START
MINIMUM INPUT
VOLTAGE TO RUN
T
A
= 25
C
SWITCH CURRENT (A)
0
0.5
1
1.5
BOOST PIN CURRENT (mA)
1766 G12
45
40
35
30
25
20
15
10
5
0
T
A
= 25
C
JUNCTION TEMPERATURE (
C)
50
1.5
1.7
2.1
25
75
1766 G13
1.3
1.1
25
0
50
100
125
0.9
0.7
1.9
THRESHOLD VOLTAGE (V)
SWITCH CURRENT (A)
0
0.5
1
1.5
SWITCH VOLTAGE (mV)
1766 G14
450
400
350
300
250
200
150
100
50
0
T
J
= 125
C
T
J
= 25
C
T
J
= 40
C
U
U
U
PI FU CTIO S
GND (Pins 1, 8, 9, 16, 17): The GND pin connections act
as the reference for the regulated output, so load regula-
tion will suffer if the "ground" end of the load is not at the
same voltage as the GND pins of the IC. This condition will
occur when load current or other currents flow through
metal paths between the GND pins and the load ground.
Keep the paths between the GND pins and the load ground
short and use a ground plane when possible. The GND pin
also acts as a heat sink and should be soldered to a large
copper plane to reduce thermal resistance. For the FE
package, the exposed pad should be soldered to the
copper ground plane underneath the device. (See Applica-
tions Information--Layout Considerations.)
SW (Pin 2): The switch pin is the emitter of the on-chip
power NPN switch. This pin is driven up to the input pin
voltage during switch on time. Inductor current drives the
switch pin negative during switch off time. Negative volt-
age is clamped with the external catch diode. Maximum
negative switch voltage allowed is 0.8V.
NC (Pins 3, 5, 7, 13): No Connection.
Switch Minimum ON Time
vs Temperature
JUNCTION TEMPERATURE (
C)
50
SWITCH MINIMUM ON TIME (ns)
400
500
600
25
75
1766 G15
300
200
25
0
50
100
125
100
0
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