LT1950
Single Switch PWM
Controller with Auxiliary
Boost Converter
DESCRIPTIO
The LT
®
1950 is a wide input range, forward, boost, flyback
and SEPIC controller that drives an N-channel power
MOSFET with few external components required.
A resistor programmable duty cycle clamp can be used to
generate a volt-second clamp for forward converter appli-
cations. An internal boost switcher is available for creating
a separate supply for the output gate driver, allowing 10V
gate drive from input voltages as low as 3V. The LT1950’s
operating frequency can be set with an external resistor
over a 100kHz to 500kHz range and a SYNC pin allows the
part to be synchronized to an external clock. Additional
programmability exists for leading edge blanking and
slope compensation.
A fast current sense comparator achieves 60ns current
sense delay and the error amplifier is a true voltage mode
error amplifier, allowing a wide range of compensation
networks. An accurate shutdown pin with programmable
hysteresis is available for undervoltage lockout and shut-
down. The LT1950 is available in a small 16-Pin SSOP
package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
FEATURES
■
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■
■
■
■
■
■
■
■
■
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■
Wide Input Range: 3V to 25V
Programmable Volt-Second Clamp
Output Power Levels from 25W to 500W
Auxiliary Boost Converter Provides 10V Gate Drive
from V
IN
as Low as 3V
Programmable Operating Frequency (100kHz to
500kHz) with One External Resistor
Programmable Slope Compensation
Programmable Leading Edge Blanking
±2%
Internal 1.23V Reference
Accurate Shutdown Pin Threshold with
Programmable Hysteresis
60ns Current Sense Delay
2.5V Auxiliary Reference Output
Synchronizable to an External Clock up to 1.5 • f
OSC
Current Mode Control
Small 16-Pin SSOP Package
APPLICATIO S
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Telecom Power Supplies
Automotive Power Supplies
Portable Electronic Equipment
Isolated and Nonisolated DC/DC Converters
TYPICAL APPLICATIO
36V to 72V DC to 26V/5A (Single Switch) Forward Converter
10V
BIAS
SLOPE
2.5V
0.1µF
249k
V
REF
BOOST
R
OSC
V
IN
V
IN2
V
SEC
SHDN
1µF
18k
Si7450
470k
PA0581
47µF
V
IN
MBRB20200
47µH
V
OUT
26V
5A
EFFICIENCY (%)
LT1950
BLANK
SYNC
GND
FB
GATE
I
SENSE
PGND
COMP
4.7k
0.015Ω
4.99k
0.022µF
100k
1950 TA01a
U
95
90
85
80
75
U
U
Efficiency vs Load Current
V
IN
= 36V
V
IN
= 48V
V
IN
= 72V
70
0.5
1.5
3.5
4.5
2.5
LOAD CURRENT (A)
5.5
1950 TA01b
1950fa
1
LT1950
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
COMP 1
FB 2
R
OSC
3
SYNC 4
SLOPE 5
V
REF
6
SHDN 7
GND 8
16 V
SEC
15 V
IN
14 BOOST
13 PGND
12 GATE
11 V
IN2
10 I
SENSE
9
BLANK
BOOST ....................................................... –0.3V to 35V
V
IN
, V
IN2
, SHDN ......................................... –0.3V to 25V
FB, SYNC, V
SEC
........................................... –0.3V to 6V
COMP, BLANK .......................................... –0.3V to 3.5V
SLOPE ...................................................... –0.3V to 2.5V
I
SENSE
......................................................... –0.3V to 1V
R
OSC
.................................................................... –50µA
V
REF
.................................................................... –10mA
Operating Junction Temperature Range
LT1950EGN/LT1950IGN (Notes 2, 5) ... – 40°C to 125°C
Storage Temperature Range ..................–65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LT1950EGN
LT1950IGN
GN PART MARKING
1950E
1950I
GN PACKAGE
16-LEAD NARROW PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 110°C/W,
θ
JC
(PIN 8) = 30°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. COMP = open, FB = 1.4V, R
OSC
= 249k, SYNC = 0V, SLOPE = open, V
REF
= 0.1µF, SHDN = V
IN
, BLANK = 0V, I
SENSE
= 0V, V
IN2
= 15V, GATE = 1nF, BOOST = open, V
IN
= 15V, V
SEC
= 0V, unless otherwise
specified.
PARAMETER
PWM Controller
Operating Input Voltage
Minimum Start-Up Voltage
V
IN
Quiescent Current
V
IN
Shutdown Current
Shutdown Threshold
Shutdown Pin Current
Shutdown Pin Current Hysteresis
V
IN2
Quiescent Current
V
IN2
Shutdown Current
V
REF
(External Output)
Output Voltage
Line Regulation
Load Regulation
Oscillator
Frequency: f
OSC
Minimum Programmable f
OSC
Maximum Programmable f
OSC
SYNC Input Resistance
SYNC Switching Threshold
SYNC Frequency/f
OSC
f
OSC
Line Reg
V
ROSC
(R
OSC
= 249k, f
OSC
=200kHz), FB = 1V (Note 7)
3V < V
IN
< 25V
9.5V < V
IN2
< 25V
R
OSC
= 249k, FB = 1V
R
OSC
= 499k
R
OSC
= 90.9k
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
I
VREF
= 0µA
I
VREF
= 0µA
I
VREF
= 0µA, FB = 1V, I
SENSE
= 0.2V
SHDN = 0V
3V < V
IN
< 25V
SHDN = 70mV Above Threshold
SHDN = 100mV Below Threshold
I(V
REF
) = 0µA, FB = 1V, I
SENSE
= 0.2V
SHDN = 0V, V
IN2
= 2.7V (Boost Diode from V
IN
= 3V)
I
VREF
= 0µA
I
VREF
= 0µA, 3V < V
IN
< 25V
0µA < I
VREF
< 2.5mA
●
●
●
●
MIN
3.0
TYP
MAX
25
UNITS
V
V
mA
µA
V
µA
µA
mA
µA
V
mV
mV
kHz
kHz
kHz
kΩ
V
%/V
%/V
V
1950fa
2.6
2.3
5
1.261
–7
4
1.32
–10
7
1.7
500
2.425
2.500
1
1
170
85
440
200
100
500
20
1.5
1.25
0.05
0.05
1
3.0
3.0
20
1.379
–13
10
2.5
700
2.575
5
5
230
115
560
2.2
1.5
0.15
0.25
2
U
W
U
U
W W
W
LT1950
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. COMP = open, FB = 1.4V, R
OSC
= 249k, SYNC = 0V, SLOPE = open, V
REF
= 0.1µF, SHDN = V
IN
, BLANK = 0V, I
SENSE
= 0V, V
IN2
= 15V, GATE = 1nF, BOOST = open, V
IN
= 15V, V
SEC
= 0V, unless otherwise
specified.
PARAMETER
Error Amplifier
FB Reference Voltage
FB Input Bias Current
Open Loop Voltage Gain
Unity Gain Bandwidth
COMP Source Current
COMP Sink Current
COMP High Level: V
OH
COMP Active Threshold
COMP Low Level: V
OL
Current Sense
I
SENSE
Maximum Threshold
I
SENSE
Input Bias Current
Default Blanking Time
Adjustable Blanking Time
Blanking Override Voltage–
I
SENSE
Maximum Threshold
Turn-Off Delay to Gate
Slope Compensation (Note 4)
Duty Cycle < 10%, COMP = V
OH
COMP = 2.5V, I
SENSE
= I
SENSE
Max Threshold
FB = 1V, COMP = 2V, I
SENSE
= 75mV
FB = 1V, COMP = 2V, I
SENSE
= 75mV
BLANK = 75k to Ground
BLANK = Open, COMP = 2.5V (Note 4)
COMP = 2V
I
SENSE
Max Threshold (DC < 10%) – (DC = 80%) (Note 4)
Default, R
SLOPE
=
∞
2x Default, R
SLOPE
= 8k
3x Default, R
SLOPE
= 3.3k
V
IN2
= 8V, 3V < V
IN
< 10V
V
IN2
= 8V, 3V < V
IN
< 10V
3V < V
IN
< 10V
3V < V
IN
< 10V
3V < V
IN
< 10V, FB = 1V (Note 4)
3V < V
IN
< 10V, FB = 1V (Note 4)
FB = 1V, V
IN2
= 12V, C
L
= 1nF (Notes 3, 6)
FB = 1V, V
IN2
= 12V, C
L
= 1nF (Notes 3, 6)
I
GATE
= 0µA, COMP = 2.5V, FB = 6V
I
GATE
= 20mA
I
GATE
= 200mA
I
GATE
= –20mA, V
IN2
= 12V, COMP = 2.5V, FB = 6V
I
GATE
= –200mA, V
IN2
= 12V, COMP = 2.5V, FB = 6V
FB = 1V, f
OSC
= 200kHz
10
9.75
90
95
97
11.5
●
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
●
TYP
1.230
–75
85
3
–1.1
13
2.5
1.0
0.15
MAX
1.254
–200
UNITS
V
nA
dB
MHz
3V < V
IN
< 25V, V
OL
+ 0.2V < COMP < V
OH
– 0.2
FB = FB Reference Voltage
V
OL
+ 0.2V < COMP < V
OH
– 0.2
(Note 6)
FB = 1V, COMP = 1.6V
FB = 1.4V, COMP = 1.6V
FB = 1V, I
COMP
= – 250µA
Start of GATE Switching (Duty Cycle > 0%)
FB = 1.4V, I
COMP
= 250µA
1.205
65
●
–0.3
8
–1.8
mA
mA
V
V
V
90
–125
100
–170
110
290
110
–250
mV
µA
ns
ns
15
25
60
14
28
42
40
mV
ns
mV
mV
mV
Internal Switcher
Boost Switch I
LIMIT
Boost Switch Off Time
V
IN2
: Boost Disable
V
IN2
: Boost Disable Hysteresis
V
IN2
: Gate Enable
V
IN2
: Gate Enable Hysteresis
GATE Driver Output
GATE Rise Time
GATE Fall Time
GATE Clamp Voltage
GATE Low Level
GATE High Level
Maximum Duty Cycle
50
30
13
0.25
1.2
14.5
0.4
1.75
ns
ns
V
V
V
V
V
%
70
250
9.5
7.0
125
500
11.0
–1.0
8.2
–0.6
9.27
180
1000
11.75
mA
ns
V
V
V
V
1950fa
3
LT1950
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. COMP = open, FB = 1.4V, R
OSC
= 249k, SYNC = 0V, SLOPE = open, V
REF
= 0.1µF, SHDN = V
IN
, BLANK = 0V, I
SENSE
= 0V, V
IN2
= 15V, GATE = 1nF, BOOST = open, V
IN
= 15V, V
SEC
= 0V, unless otherwise
specified.
PARAMETER
Maximum Duty Cycle Clamp
V
SEC
Input Bias Current
CONDITIONS
V
SEC
= 1.4V, FB = 1V, COMP = V
OH
0V < V
SEC
< 2.8V
MIN
63
TYP
75
–0.3
MAX
87
–1.0
UNITS
%
µA
ELECTRICAL CHARACTERISTICS
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LT1950EGN is guaranteed to meet performance specifications
from 0°C to 125°C operating 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 LT1950IGN is guaranteed over the full –40°C to 125°C operating
junction temperature range.
Note 3:
Rise and Fall times are between 10% and 90% levels.
Note 4:
Guaranteed by correlation to static test.
Note 5:
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.
Note 6:
Guaranteed but not tested.
Note 7:
Maximum recommended SYNC frequency = 500kHz.
TYPICAL PERFOR A CE CHARACTERISTICS
FB Voltage vs Temperature
1.26
1.25
FB VOLTAGE (V)
1.24
1.23
1.22
1.21
1.20
–50 –25
210
200
190
180
170
V
IN
SHUTDOWN I
Q
(µA)
FREQUENCY (kHz)
50
25
75
0
TEMPERATURE (°C)
Shutdown Threshold vs
Temperature
1.45
125
MAXIMUM I
SENSE
THRESHOLD (mV)
SHUTDOWN THRESHOLD (V)
1.40
110
105
100
95
90
85
80
75
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
I
SENSE
CURRENT (µA)
1.35
1.30
1.25
1.20
–50
–25
50
25
75
0
TEMPERATURE (°C)
4
U W
100
1950 G01
Switching Frequency vs
Temperature
240
230
220
16
14
12
10
8
6
4
2
–25
50
25
75
0
TEMPERATURE (°C)
100
125
V
IN
Shutdown I
Q
vs Temperature
SHDN = 0V
125
160
–50
0
–50
–25
50
25
75
0
TEMPERATURE (°C)
100
125
1950 • G02
1950 • G03
Maximum I
SENSE
Threshold vs
Temperature
270
250
230
210
190
170
150
130
110
I
SENSE
Pin Current vs
Temperature
120
115
100
125
90
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
1950 • G04
1950 G05
1950 G06
1950fa
LT1950
TYPICAL PERFOR A CE CHARACTERISTICS
BLANK Override Threshold –
I
SENSE
Maximum Threshold vs
Temperature
40
MINIMUM V
IN
START-UP VOLTAGE (V)
BLANK OVERRIDE THRESHOLD
–I
SENSE
MAXIMUM THRESHOLD (mV)
35
30
25
20
15
10
–50 –25
3.00
V
IN
I
Q
(mA)
50
25
75
0
TEMPERATURE (°C)
SHDN Input Current *(–1) vs
Temperature
14
SHDN INPUT CURRENT*(–1) (µA)
12
SHDN = SHDN THRESHOLD + 70mV
10
8
6
4
2
0
–50 –25
SHDN = SHDN THRESHOLD – 100mV
SHDN CURRENT HYSTERESIS (µA)
11
10
GATE RISE/FALL TIME (ns)
50
25
75
0
TEMPERATURE (°C)
V
IN2
: GATE Enable
vs Temperature
9.2
13.0
12.5
V
IN2
GATE ENABLE (V)
8.7
GATE ENABLE
8.2
HYSTERESIS
7.7
GATE DISABLE
7.2
–50 –25
12.0
11.5
BOOST SWITCH I
LIMIT
(mA)
V
IN2
BOOST DISABLE (V)
50
25
75
0
TEMPERATURE (°C)
U W
100
1950 G07
Minimum V
IN
Start-Up Voltage vs
Temperature (V
IN2
Boosted)
3.1
2.9
2.75
2.7
2.5
2.3
2.1
1.9
1.7
2.00
–50 –25
0
25
50
75
100
125
V
IN
I
Q
vs Temperature
2.50
2.25
125
1.5
–50 –25
0
25
50
75
100
125
TEMPERATURE (°C)
1950 G08
TEMPERATURE (°C)
1950 G09
SHDN Current Hysteresis vs
Temperature
125
GATE Rise/Fall Time vs
GATE Capacitance
T
A
= 25°C
100
9
8
7
6
5
4
3
–50 –25
t
r
75
t
f
50
25
0
0
25
50
75
100
125
0
TEMPERATURE (°C)
1000
3000
4000
2000
GATE CAPACITANCE (pF)
5000
1950 G12
100
125
1950 G10
1950 G11
V
IN2
: BOOST Disable
vs Temperature
250
BOOST Switch I
LIMIT
vs
Temperature
200
BOOST DISABLE
11.0
10.5
10.0
9.5
BOOST RE-ENABLE
HYSTERESIS
150
100
100
125
9.0
–50
–25
50
25
75
0
TEMPERATURE (°C)
100
125
50
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
1950 G13
1950 G14
1950 G15
1950fa
5
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