LT1370
500kHz High Efficiency
6A Switching Regulator
FEATURES
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DESCRIPTION
The LT
®
1370 is a monolithic high frequency current mode
switching regulator. It can be operated in all standard
switching configurations including boost, buck, flyback,
forward, inverting and “Cuk.” A 6A high efficiency switch
is included on the die, along with all oscillator, control and
protection circuitry.
The LT1370 typically consumes only 4.5mA quiescent
current and has higher efficiency than previous parts.
High frequency switching allows for very small inductors
to be used.
New design techniques increase flexibility and maintain
ease of use. Switching is easily synchronized to an exter-
nal logic level source. A logic low on the Shutdown pin
reduces supply current to 12µA. Unique error amplifier
circuitry can regulate positive or negative output voltage
while maintaining simple frequency compensation tech-
niques. Nonlinear error amplifier transconductance
reduces output overshoot on start-up or overload recov-
ery. Oscillator frequency shifting protects external com-
ponents during overload conditions.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Faster Switching with Increased Efficiency
Uses Small Inductors: 4.7µH
All Surface Mount Components
Low Minimum Supply Voltage: 2.7V
Quiescent Current: 4.5mA Typ
Current Limited Power Switch: 6A
Regulates Positive or Negative Outputs
Shutdown Supply Current: 12µA Typ
Easy External Synchronization
Switch Resistance: 0.065Ω Typ
APPLICATIONS
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Boost Regulators
Laptop Computer Supplies
Multiple Output Flyback Supplies
Inverting Supplies
TYPICAL APPLICATION
5V to 12V Boost Converter
5V
L1*
D1
MBRD835L
V
OUT
12V
R1
53.6k
1%
92
†
90
V
IN
OFF
ON
S/S
LT1370
V
SW
EFFICIENCY (%)
88
86
84
82
80
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
LOAD CURRENT (A)
LT1370 • TA02
+
C1**
22µF
25V
FB
GND
C2
0.047µF
R3
2k
V
C
+
R2
6.19k
1%
C3
0.0047µF
LT1370 • TA01
C4**
22µF
25V
×
2
*COILTRONICS
UP2-4R7 (4.7µH)
UP4-100 (10µH)
**AVX TPSD226M025R0200
†
MAX I
OUT
L1
I
OUT
4.7µH 1.8A
10µH 2A
U
U
U
12V Output Efficiency
V
IN
= 5V
L = 10µH
sn1370 1370fs
1
LT1370
ABSOLUTE
AXI U
RATI GS
Operating Ambient Temperature Range ...... 0°C to 70°C
Operating Junction Temperature Range
Commercial .......................................... 0°C to 125°C
Industrial ......................................... – 40°C to 125°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
Supply Voltage ....................................................... 30V
Switch Voltage
LT1370 ............................................................... 35V
LT1370HV .......................................................... 42V
S/S, SHDN, SYNC Pin Voltage ................................ 30V
Feedback Pin Voltage (Transient, 10ms) ..............
±10V
Feedback Pin Current ........................................... 10mA
Negative Feedback Pin Voltage
(Transient, 10ms) .............................................
±10V
PACKAGE/ORDER I FOR ATIO
FRONT VIEW
7
6
5
4
3
2
1
R PACKAGE
7-LEAD PLASTIC DD
T
JMAX
= 125°C,
θ
JA
= 30°C/W,
θ
JC
= 4°C/W
WITH PACKAGE SOLDERED TO 0.5 INCH
2
COPPER
AREA OVER BACKSIDE GROUND PLANE OR INTERNAL
POWER PLANE.
θ
JA
CAN VARY FROM 20°C/W TO
> 40°C/W DEPENDING ON MOUNTING TECHNIQUE
TAB
IS
GND
V
IN
NFB
V
SW
GND
S/S
FB
V
C
ORDER PART
NUMBER
LT1370CR
LT1370HVCR
LT1370IR
LT1370HVIR
TAB
IS
GND
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
V
IN
= 5V, V
C
= 0.6V, V
FB
= V
REF
, V
SW
, S/S and NFB pins open, T
A
= 25°C unless otherwise noted.
SYMBOL
V
REF
I
FB
PARAMETER
Reference Voltage
Feedback Input Current
Reference Voltage Line Regulation
V
NFR
I
NFB
Negative Feedback Reference Voltage
Negative Feedback Input Current
Negative Feedback Reference Voltage
Line Regulation
g
m
Error Amplifier Transconductance
Error Amplifier Source Current
Error Amplifier Sink Current
CONDITIONS
Measured at Feedback Pin
V
C
= 0.8V
V
FB
= V
REF
●
●
2.7V
≤
V
IN
≤
25V, V
C
= 0.8V
Measured at Negative Feedback Pin
Feedback Pin Open, V
C
= 0.8V
V
NFB
= V
NFR
2.7V
≤
V
IN
≤
25V, V
C
= 0.8V
∆I
C
=
±25µA
V
FB
= V
REF
– 150mV, V
C
= 1.5V
V
FB
= V
REF
+ 150mV, V
C
= 1.5V
2
U
U
W
W W
U
W
FRONT VIEW
7
6
5
4
3
2
1
T7 PACKAGE
7-LEAD TO-220
T
JMAX
= 125°C,
θ
JA
= 50°C/W,
θ
JC
= 4°C/W
V
IN
NFB
V
SW
GND
S/S
FB
V
C
ORDER PART
NUMBER
LT1370CT7
LT1370HVCT7
LT1370IT7
LT1370HVIT7
MIN
1.230
1.225
TYP
1.245
1.245
250
MAX
1.260
1.265
550
900
0.03
– 2.435
– 2.400
– 15
0.05
1900
2300
350
2400
UNITS
V
V
nA
nA
%/V
V
V
µA
%/V
µmho
µmho
µA
µA
sn1370 1370fs
●
0.01
– 2.48
– 2.48
– 30
0.01
1100
700
120
1500
200
1400
– 2.525
●
– 2.560
●
●
– 45
●
●
●
LT1370
ELECTRICAL CHARACTERISTICS
V
IN
= 5V, V
C
= 0.6V, V
FB
= V
REF
, V
SW
, S/S and NFB pins open, T
A
= 25°C unless otherwise noted.
SYMBOL
PARAMETER
Error Amplifier Clamp Voltage
A
V
f
Error Amplifier Voltage Gain
V
C
Pin Threshold
Switching Frequency
Duty Cycle = 0%
2.7V
≤
V
IN
≤
25V
0°C
≤
T
J
≤
125°C
– 40°C
≤
T
J
≤
0°C (I-Grade)
●
●
CONDITIONS
High Clamp, V
FB
= 1V
Low Clamp, V
FB
= 1.5V
MIN
1.5
0.2
0.9
460
440
400
85
35
42
40
6
TYP
1.8
0.3
500
1.1
500
500
95
130
MAX
2.30
0.52
1.35
550
580
580
300
UNITS
V
V
V/ V
V
kHz
kHz
kHz
%
ns
V
V
V
Maximum Switch Duty Cycle
Switch Current Limit Blanking Time
BV
Output Switch Breakdown Voltage
LT1370
●
●
LT1370HVC, 0°C
≤
T
J
≤
125°C
LT1370HVI, – 40°C
≤
T
J
≤
0°C (I-Grade)
I
SW
= 6A
Duty Cycle = 50%
Duty Cycle = 80% (Note 1)
●
●
44
47
0.065
8
7
22
10
0.11
10
33
V
SAT
I
LIM
∆I
IN
∆I
SW
Output Switch ON Resistance
Switch Current Limit
Supply Current Increase During Switch ON Time
Control Voltage to Switch Current
Transconductance
Minimum Input Voltage
Ω
A
A
mA/A
A/V
●
2.4
4.5
12
0.6
4
–7
600
1.3
12
2.7
6
40
2
25
10
800
V
mA
µA
V
µs
µA
kHz
I
Q
Supply Current
Shutdown Supply Current
Shutdown Threshold
Shutdown Delay
S/S Input Current
Synchronization Frequency Range
2.7V
≤
V
IN
≤
25V
2.7V
≤
V
IN
≤
25V, V
S/S
≤
0.6V
2.7V
≤
V
IN
≤
25V
0V
≤
S/S
≤
5V
●
●
●
●
●
●
The
●
denotes specifications which apply over the full operating
temperature range.
Note 1:
For duty cycles (DC) between 45% and 85%, minimum switch
current limit is given by I
LIM
= 2.65(2.7 – DC).
sn1370 1370fs
3
LT1370
TYPICAL PERFORMANCE CHARACTERISTICS
Switch Saturation Voltage
vs Switch Current
550
500
450
125°C
75°C
25°C
SWITCH CURRENT LIMIT (A)
8.2
8.0
7.8
SWITCH VOLTAGE (mV)
INPUT VOLTAGE (V)
400
350
300
250
200
150
100
50
0
0
1
0°C
4
2
3
SWITCH CURRENT (A)
Shutdown Delay and Threshold
vs Temperature
MINIMUM SYNCHRONIZATION VOLTAGE (V
P-P
)
20
18
16
SHUTDOWN DELAY (µs)
1.8
SHUTDOWN THRESHOLD
1.6
1.4
1.2
1.0
SHUTDOWN DELAY
0.8
0.6
0.4
0.2
0
0
25 50 75 100 125 150
TEMPERATURE (°C)
LT1370 • G04
ERROR AMPLIFIER OUTPUT CURRENT (µA)
14
12
10
8
6
4
2
0
–50 –25
S/S Pin Input Current vs Voltage
2
110
SWITCHING FREQUENCY (% OF TYPICAL)
TRANSCONDUCTANCE (µmho)
1
INPUT CURRENT (µA)
0
–1
–2
–3
–4
–1
0
1
2
3
4
VOLTAGE (V)
5
6
7
4
U W
5
6
LT1370 • G01
LT1370 • G07
Switch Current Limit
vs Duty Cycle
3.0
2.8
2.6
2.4
2.2
2.0
Minimum Input Voltage
vs Temperature
7.6
7.4
7.2
7.0
6.8
6.6
0
10 20 30 40 50 60 70 80 90 100
DUTY CYCLE (%)
LT1370 • G02
1.8
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
LT1370 • G03
Minimum Synchronization
Voltage vs Temperature
2.0
3.0
2.5
2.0
1.5
1.0
0.5
0
–50 –25
f
SYNC
= 700kHz
400
300
200
100
0
–100
–200
–300
Error Amplifier Output Current
vs Feedback Pin Voltage
25°C
–55°C
125°C
SHUTDOWN THRESHOLD (V)
0
25 50 75 100 125 150
TEMPERATURE (°C)
LT1370 • G05
–0.3
V
REF
–0.2
–0.1
FEEDBACK PIN VOLTAGE (V)
0.1
LT1370 • G06
Switching Frequency
vs Feedback Pin Voltage
2000
1800
1600
1400
1200
1000
800
600
400
200
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
FEEDBACK PIN VOLTAGE (V)
LT1370 • G08
Error Amplifier Transconductance
vs Temperature
g
m
=
∆I
(V
C
)
∆V
(FB)
100
90
80
70
60
50
40
30
20
10
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
LT1370 • G09
sn1370 1370fs
LT1370
TYPICAL PERFORMANCE CHARACTERISTICS
V
C
Pin Threshold and High
Clamp Voltage vs Temperature
2.2
2.0
FEEDBACK INPUT CURRENT (nA)
700
600
500
400
300
200
100
V
FB
=V
REF
NEGATIVE FEEDBACK INPUT CURRENT (µA)
V
C
VOLTAGE (V)
1.8
1.6
1.4
1.2
V
C
HIGH CLAMP
V
C
THRESHOLD
1.0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
LT1370 • G10
PIN FUNCTIONS
V
C
:
The Compensation pin is used for frequency compen-
sation, current limiting and soft start. It is the output of the
error amplifier and the input of the current comparator.
Loop frequency compensation can be performed with an
RC network connected from the V
C
pin to ground. See
Applications Information.
FB:
The Feedback pin is used for positive output voltage
sensing and oscillator frequency shifting. It is the invert-
ing input to the error amplifier. The noninverting input of
this amplifier is internally tied to a 1.245V reference.
NFB:
The Negative Feedback pin is used for negative
output voltage sensing. It is connected to the inverting
input of the negative feedback amplifier through a 100k
source resistor.
S/S:
Shutdown and Synchronization Pin. The S/S pin is
logic level compatible. Shutdown is active low and the
shutdown threshold is typically 1.3V. For normal opera-
tion, pull the S/S pin high, tie it to V
IN
or leave it floating. To
synchronize switching, drive the S/S pin between 600kHz
and 800kHz. See Applications Information.
V
IN
:
Bypass Input Supply Pin with a Low ESR Capacitor,
10µF or More. The regulator goes into undervoltage lock-
out when V
IN
drops below 2.5V. Undervoltage lockout
stops switching and pulls the V
C
pin low.
V
SW
:
The Switch pin is the collector of the power switch
and has large currents flowing through it. Keep the traces
to the switching components as short as possible to
minimize radiation and voltage spikes.
GND:
Tie all ground pins to a good quality ground plane.
See Applications Information.
U W
Feedback Input Current
vs Temperature
800
Negative Feedback Input Current
vs Temperature
0
V
NFB
=V
NFR
–10
–20
–30
–40
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
LT1370 • G11
–50
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
LT1370 • G12
U
U
U
sn1370 1370fs
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