LT1766/LT1766-5
5.5V to 60V 1.5A, 200kHz
Step-Down Switching Regulator
FEATURES
s
s
s
s
s
DESCRIPTIO
s
s
s
s
s
s
s
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.
*Patent # 6, 498, 466
APPLICATIO S
s
s
s
s
s
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
1766fa
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
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
ORDER PART
NUMBER
LT1766EFE
LT1766IFE
LT1766EFE-5
LT1766IFE-5
FE PACKAGE
16-LEAD PLASTIC TSSOP
T
JMAX
= 125°C,
θ
JA
= 45°C/W,
θ
JC
(PAD) = 10°C/W
EXPOSED PAD (PIN 17) IS GND.
MUST BE SOLDERED TO PCB
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
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.
PARAMETER
Reference Voltage (V
REF
) (LT1766)
SENSE Voltage (LT1766-5)
SENSE Pin Resistance (LT1766-5)
FB Input Bias Current (LT1766)
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
FB = 1V or V
SENSE
= 4.1V
FB = 1.4V or V
SENSE
= 5.7V
Duty Cycle = 0
SHDN = 1V
q
q
q
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
q
q
(Notes 2, 9)
dl (V
C
) =
±10µA
(Note 9)
q
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
ORDER PART
NUMBER
LT1766EGN
LT1766IGN
LT1766EGN-5
LT1766IGN-5
GN PART MARKING
1766
1766I
17665
1766I5
GN PACKAGE
16-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 85°C/W,
θ
JC
(PIN 8) = 25°C/W
FOUR CORNER PINS SOLDERED
TO GROUND PLANE
MIN
1.204
1.195
4.94
4.90
9.5
200
1500
1000
125
100
TYP
1.219
5
13.8
–0.5
400
2000
1.7
225
225
0.9
2.1
MAX
1.234
1.243
5.06
5.10
19
–1.5
3000
4200
400
450
UNITS
V
V
V
V
kΩ
µA
V/V
µMho
µMho
A/V
µA
µA
V
V
1766fa
LT1766/LT1766-5
ELECTRICAL CHARACTERISTICS
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.
PARAMETER
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
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.
CONDITIONS
V
C
Open, Boost = V
IN
+ 5V, FB = 1V or V
SENSE
= 4.1V
I
SW
= 1.5A, Boost = V
IN
+ 5V (Note 7)
q
q
MIN
1.5
TYP
2
0.2
MAX
3
0.3
0.4
UNITS
A
Ω
Ω
%
%
FB = 1V or V
SENSE
= 4.1V
q
93
90
184
172
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
25
70
2.2
4.2
75
200
2.53
0.6
0.6
2.2
700
20
V
C
Set to Give DC = 50%
q
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
≤
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
q
q
q
q
q
q
V
C
Open
V
C
Open, Shutting Down
V
C
Open, Starting Up
q
q
q
q
2.3
0.15
0.25
228
2.42
0.37
0.45
1.5
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.
1766fa
3
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
–50
–25
0
25
50
75
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
4
U W
100
FB Pin Voltage and Current
2.0
250
200
1.5
1.224
150
100
12
6
0
125
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
100
25
75
–50 –25
0
JUNCTION TEMPERATURE (°C)
0
50
100
–50 –25
25
75
0
JUNCTION TEMPERATURE (°C)
125
1766 G02
1766 G03
Shutdown Supply Current
40
300
250
V
SHDN
= 0V
35 T
A
= 25°C
30
25
20
15
10
5
0
125
Shutdown Supply Current
T
A
= 25°C
V
IN
= 60V
200
V
IN
= 15V
150
100
50
0
0
10
20
30
40
INPUT VOLTAGE (V)
50
60
1766 G05
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
500
100
1k
10k
100k
FREQUENCY (Hz)
1M
–50
10M
1766 G08
1766fa
LT1766/LT1766-5
TYPICAL PERFOR A CE CHARACTERISTICS
Switching Frequency
230
220
7.5
BOOST PIN CURRENT (mA)
INPUT VOLTAGE (V)
FREQUENCY (kHz)
210
200
190
180
170
–50
–25
0
25
50
75
JUNCTION TEMPERATURE (°C)
1766 G10
V
C
Pin Shutdown Threshold
2.1
1.9
SWITCH MINIMUM ON TIME (ns)
THRESHOLD VOLTAGE (V)
1.7
1.5
1.3
1.1
0.9
0.7
50
100
–50 –25
25
75
0
JUNCTION TEMPERATURE (°C)
SWITCH VOLTAGE (mV)
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.
1766fa
U W
100
1766 G13
Minimum Input Voltage with 5V
Output
T
A
= 25°C
45
40
7.0
35
30
25
20
15
10
5
1
0
BOOST Pin Current
T
A
= 25°C
6.5
MINIMUM INPUT
VOLTAGE TO START
6.0
5.5
MINIMUM INPUT
VOLTAGE TO RUN
125
5.0
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
LOAD CURRENT (A)
0
0.5
1
SWITCH CURRENT (A)
1.5
1766 G12
1766 G11
Switch Voltage Drop
450
400
350
300
250
200
150
100
50
125
600
Switch Minimum ON Time
vs Temperature
T
J
= 125°C
500
400
300
200
100
0
50
100
25
75
–50 –25
0
JUNCTION TEMPERATURE (°C)
T
J
= 25°C
T
J
= –40°C
0
0
0.5
1
SWITCH CURRENT (A)
1.5
1766 G14
125
1766 G15
U
U
U
5
