LT1680
High Power DC/DC
Step-Up Controller
FEATURES
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DESCRIPTION
The LT
®
1680 is a high power, current mode switching
power supply controller optimized for boost topologies.
The IC drives N-channel MOSFET switches for DC/DC
converters in applications up to 60V input. A high current
gate drive output handles up to 10,000pF gate capaci-
tance, enabling the construction of high power DC/DC
converters. Current sense common mode range up to 60V
allows current sensing to be referenced to the input
supply, eliminating the need for sense blanking circuits.
The LT1680 incorporates programmable average current
limiting allowing accurate limiting of DC current in the
magnetics, independent of ripple current . User adjustable
slope compensation provides stable operation at duty
cycles up to 90%.
The LT1680 operating frequency is programmable and
can be synchronized up to 200kHz. Minimum off-time
operation provides switch protection. The IC also incorpo-
rates a soft start feature that is gated by both shutdown
and undervoltage lockout conditions.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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High Voltage: Operation Up to 60V Max
High Current: N-Channel Drive Handles Up to
10,000pF Gate Capacitance
Programmable Average Current Limiting
5V Reference Output with 10mA External
Loading Capability
Fixed Frequency Current Mode Operation
Oscillator Synchronizable Up to 200kHz
Undervoltage Lockout with Hysteresis
Programmable Start Inhibit for Power Supply
Sequencing and Protection
User Adjustable Slope Compensation
APPLICATIONS
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High Power Single Board Systems
Distributed Power Converters
Industrial Control Systems
Lead-Acid Battery Back-Up Systems
Automotive and Heavy Equipment
TYPICAL APPLICATION
12V to 48V, 250W Boost
12V
IN
10V TO 15V
24A (DC) R
SENSE
0.005Ω
C2
1µF
R
CT
15k
LT1680
1
2
C3 2.2nF
C4 0.22µF
C
VC
4.7nF
1N914
R
VC
4.7k
3
4
5
6
7
8
C6 0.1µF
R7
2k
SL/ADJ
C
T
I
AVG
SS
V
C
5V
REF
SYNC
12V
IN
GATE
PGND
SENSE
–
SENSE
+
16
15
14
13
12
11
10
9
R6
75k
+
+
C
CT
1nF
C
IN
680µF
25V
×4
C12
1µF
L1
25µH
EFFICIENCY (%)
M1
IRFZ44
×
3
SGND RUN/SHDN
V
FB
V
REF
R9
100k
MBR0520
C11 1nF
D1
MBR20100CT
×
2
+
L1: Kool Mµ
®
, 18T #14 ON 77314-A7
Kool Mµ IS A REGISTERED TRADEMARK OF MAGNETICS, INC.
C
OUT
680µF
63V
1680 TA01
×3
V
OUT
48V
5.2A
U
U
U
Efficiency vs Output Power
100
V
OUT
= 48V
95
90
85
80
75
0
50
150
200
100
OUTPUT POWER (W)
250
1680 TA02
1
LT1680
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW
SL/ADJ
C
T
I
AVG
SS
V
C
SGND
V
FB
V
REF
1
2
3
4
5
6
7
8
16 5V
REF
15 SYNC
14 12V
IN
13 GATE
12 PGND
11 RUN/SHDN
10 SENSE
–
9
SENSE
+
Power Supply Voltage (12V
IN
) .................. – 0.3V to 20V
Sense Amplifier Input Common Mode ...... – 0.3V to 60V
GATE Pin Voltage....................... – 0.3V to 12V
IN
+ 0.3V
RUN/SHDN Pin Voltage ......................... – 0.3V to 12V
IN
All Other Pin Voltages ................................. – 0.3V to 7V
5V Reference Output Current ............................... 65mA
Operating Ambient Temperature Range
LT1680C .................................................. 0°C to 70°C
LT1680I .............................................. – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
ORDER PART
NUMBER
LT1680CN
LT1680CSW
LT1680IN
LT1680ISW
N PACKAGE
16-LEAD PDIP
SW PACKAGE
16-LEAD PLASTIC SO WIDE
T
JMAX
= 125°C,
θ
JA
= 75°C/ W (N)
T
JMAX
= 125°C,
θ
JA
= 90°C/ W (SW)
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
12V
IN
= 12V, V
VC
= 2V, V
FB
= V
REF
= 1.25V, C
GATE
= 3000pF, T
A
= 25°C unless otherwise noted.
SYMBOL
I
12VIN
PARAMETER
DC Active Supply Current (Note 2)
DC Standby Supply Current
V
RUN/SHDN
Shutdown Rising Threshold
V
SSHYST
I
SS
V
UVLO
Shutdown Threshold Hysteresis
Soft Start Charge Current
Undervoltage Lockout Threshold - Falling
Undervoltage Lockout Threshold - Rising
Undervoltage Lockout Hysteresis
5V Reference Voltage
5V Reference Line Regulation
I
REF5
5V Reference Load Range - DC
Pulse
5V Reference Load Regulation
I
SC
V
FB
I
FB
g
m
A
V
I
VC
V
VC
5V Reference Short-Circuit Current
Error Amplifier Reference Voltage
Feedback Input Current
Error Amplifier Transconductance
Error Amplifier Voltage Gain
Error Amplifier Source Current
Error Amplifier Sink Current
Absolute V
C
Clamp Voltage
V
FB
– V
REF
= 500mV
Measured at V
C
Pin
Measured at Feedback Pin
q
q
q
q
q
CONDITIONS
Gate Output On
Gate Output Off
V
RUN
< 0.5V
q
q
q
MIN
TYP
15
12
65
MAX
22
110
1.35
14
9.75
9.95
UNITS
mA
mA
µA
V
mV
µA
V
V
mV
V
mV/V
mA
mA
V/A
mA
Supply and Protection
1.15
5
8.20
200
4.75
1.25
15
8
9.00
9.35
350
5
3
5V Reference
V
REF5
Line, Load and Temperature
10V
≤
12V
IN
≤
15V
q
q
q
q
5.25
5
10
20
0
≤
I
REF5
≤
20mA
q
–1.25
45
1.242
1.235
0.1
1200
1500
200
280
1.250
0.5
2000
3000
275
400
3.5
–2
Error Amplifier
1.258
1.265
1.0
3200
V
V
µA
µmho
V/V
µA
µA
V
V
FB
= V
REF
q
q
q
q
q
2
U
W
U
U
W W
W
LT1680
ELECTRICAL CHARACTERISTICS
12V
IN
= 12V, V
VC
= 2V, V
FB
= V
REF
= 1.25V, C
GATE
= 3000pF, T
A
= 25°C unless otherwise noted.
SYMBOL
V
SENSE
V
IAVG
A
V
V
OS
I
BIAS
Oscillator
f
O
I
CT
V
SYNC
f
SYNC
V
GATE
Operating Frequency, Free Run
Frequency Programming Error
Timing Capacitor Discharge Current
SYNC Input Threshold
SYNC Frequency Range
Undervoltage Output Clamp
Standby Mode Output Clamp
Gate Output On Voltage
Gate Output Off Voltage
Gate Output Rise Time
Gate Output Fall Time
f
O
≤
200kHz, R
CT
= 16.9k, C
CT
= 1000pF
LT1680C
LT1680I
Rising Edge
f
SYNC
≤
200kHz
12V
IN
≤
8.2V
V
RUN
< 0.5V
q
q
q
q
q
q
PARAMETER
Peak Current Limit Threshold
Average Current Limit Threshold
Average Current Limit Threshold
Amplifier DC Gain
Amplifier Input Offset Voltage
Input Bias Current
CONDITIONS
Measured at Sense Inputs
Measured at Sense Inputs, V
CMSENSE
= 10V
Measured at I
AVG
Pin
Measured at I
AVG
Pin
2V < V
CMSENSE
< 60V,
SENSE
+
– SENSE
–
= 5mV
Sink (V
CMSENSE
> 5V)
Source (V
CMSENSE
= 0V)
q
q
q
q
q
MIN
170
110
TYP
190
120
2.5
15
MAX
UNITS
mV
mV
V
V/V
mV
Error Amplifier
130
Current Sense Amplifier
0.1
45
700
75
1200
200
5
2.5
2.5
2.75
2.75
2.0
1.4f
O
0.4
11
11.9
0.4
60
60
0.7
0.1
12
0.7
200
140
V
V
V
V
ns
ns
µA
µA
kHz
%
mA
mA
V
–5
2.20
2.10
0.8
f
O
Output Drivers
q
q
q
q
q
q
t
GATER
t
GATEF
The
q
denotes specifications which apply over the full operating
temperature range.
Note 1:
Absolute Maximum Ratings are those values beyond which the life of
a device may be impaired.
Note 2:
Supply current specification does not include external FET gate
charge currents. Actual supply currents will be higher and vary with
operating frequency, operating voltages and the type of external FETs used.
See Applications Information.
3
LT1680
TYPICAL PERFORMANCE CHARACTERISTICS
I
12VIN
Supply Current
vs Temperature
19
18
I
12VIN
SUPPLY CURRENT (mA)
I
12VIN
SUPPLY CURRENT (mA )
17
16
15
14
13
12
11
–50 –25
0
25
50
75
100
125
C
G
= 10nF
30
GATE TRANSITION TIME (ns)
TEMPERATURE (°C)
1680 G01
5V
REF
Short-Circuit Current
vs Temperature
60
5V
REF
SHORT-CIRCUIT CURRENT (mA)
5V
REF
= 0V
I
12VIN
SHUTDOWN CURRENT (µA)
55
50
45
40
35
30
– 50 –25
V
REF
VOLTAGE (V)
50
25
75
0
TEMPERATURE (°C)
5V
REF
Voltage
vs Temperature
5.01
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
–50 –25
ERROR AMPLIFIER TRANSCONDUCTANCE (m )
ERROR AMPLIFIER VOLTAGE GAIN (kV/V)
5V
REF
VOLTAGE (V)
5.00
4.99
4.98
–50 –25
50
25
75
0
TEMPERATURE (°C)
4
U W
100
1680 G04
I
12VIN
Supply Current
vs 12V
IN
Supply Voltage
40
f
O
= 150kHz
T
A
= 25°C
35
Gate Transition Time vs C
GATE
150
130
110
90
70
50
30
•
•
•
•
T
A
= 25°C
•
t
f
t
r
25
C
G
= 4.7nF
•
•
20
C
G
= 3.3nF
C
G
= 1nF
10
12
13
14
11
12V
IN
SUPPLY VOLTAGE (V)
15
1680 G02
15
0
2500
5000
C
GATE
(pF)
7500
10000
1680 G03
I
12VIN
Shutdown Current
vs Temperature
80
75
70
65
60
55
50
–50 –25
V
REF
Voltage
vs Temperature
1.252
1.251
1.250
1.249
1.248
1.247
1.246
–50 –25
125
50
25
75
0
TEMPERATURE (°C)
100
125
50
25
75
0
TEMPERATURE (°C)
100
125
1680 G05
1680 G06
Error Amplifier Voltage Gain
vs Temperature
2.6
2.4
2.2
2.0
1.8
1.6
Error Amplifier Transconductance
vs Temperature
Ω
100
125
50
25
75
0
TEMPERATURE (°C)
100
125
1.4
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
1680 G07
1680 G08
1680 G09
LT1680
TYPICAL PERFORMANCE CHARACTERISTICS
Error Amplifier Source Current
vs Temperature
ERROR AMPLIFIER SOURCE CURRENT (µA)
350
325
300
275
250
225
200
–50 –25
SS OUTPUT CURRENT (µA)
RUN/SHDN RISING THRESHOLD (V)
50
25
75
0
TEMPERATURE (°C)
RUN/SHDN Threshold Hysteresis
vs Temperature
14
RUN/SHDN THRESHOLD HYSTERESIS (mV)
13
12
11
10
9
8
–50 –25
V
SENSE
(mV)
120
110
100
90
TYPICAL
LOWER LIMIT
V
12VIN
(V)
50
25
75
0
TEMPERATURE (°C)
Sense Amplifier Input Bias
Current (Source) vs Temperature
1200
V
CMSENSE
= 0V
1100
1000
V
CMSENSE
= 10V
55
50
45
40
35
30
–50 –25
RUN/SHDN INPUT CURRENT (nA )
700
600
500
400
300
200
100
0
0
FULL OPERATING
TEMPERATURE
RANGE
800
700
600
500
400
–50 –25
0
25
50
75
100
125
I
B(SINK)
(µA)
900
..................................................................
I
B(SOURCE)
(µA)
TEMPERATURE (°C)
1680 G16
U W
100
1680 G10
SS Output Current
vs Temperature
9
1.26
1.25
1.24
1.23
1.22
1.21
RUN/SHDN Rising Threshold
vs Temperature
8
7
125
6
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
1.20
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
1680 G11
1680 G12
Average Current Limit Threshold
Sense Voltage vs Common Mode
Voltage
160
150
140
UPPER LIMIT
130
FULL OPERATING
TEMPERATURE RANGE
UVLO Thresholds vs Temperature
10.00
9.75
9.50
9.25
9.00
8.75
8.50
8.25
FALLING
RISING
100
125
80
0
1
2
3
4
5
60
1680 G14
8.00
–50 –25
0
25
50
75
100
125
V
SENSE(CM)
(V)
1680 G13
TEMPERATURE (°C)
1680 G15
Sense Amplifier Input Bias
Current (Sink) vs Temperature
60
800
RUN/SHDN Input Current
vs Pin Voltage
UPPER
LIMIT
TYPICAL
LOWER
LIMIT
50
25
75
0
TEMPERATURE (°C)
100
125
1.0 (1.25) 1.5
0.5
RUN/SHDN PIN VOLTAGE (V)
2.0
1680 G18
1680 G17
5
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