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LT1370HVCR#PBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16
4
LT1370
sn1370 1370fs
TYPICAL PERFORMANCE CHARACTERISTICS
U
W
Switching Frequency
vs Feedback Pin Voltage
VOLTAGE (V)
–1
INPUT CURRENT (µA)
1
7
LT1370 • G07
–1
–3
0
2
–2
–4
1
3
5
0
2
4
6
FEEDBACK PIN VOLTAGE (V)
0
SWITCHING FREQUENCY (% OF TYPICAL)
70
90
110
0.8
LT1370 • G08
50
30
60
80
100
40
20
10
0.2
0.4
0.6
0.1 0.9
0.3
0.5
0.7
1.0
Switch Saturation Voltage
vs Switch Current
DUTY CYCLE (%)
6.6
SWITCH CURRENT LIMIT (A)
7.4
7.2
7.8
8.2
7.0
6.8
7.6
8.0
20 40 60 80
LT1370 • G02
10010
0
30 50 70 90
Switch Current Limit
vs Duty Cycle
SWITCH CURRENT (A)
0
SWITCH VOLTAGE (mV)
300
400
550
5
LT1370 • G01
200
100
250
350
450
500
150
50
0
1
23
4
6
125°C
75°C
25°C
0°C
TEMPERATURE (°C)
–50
1.8
INPUT VOLTAGE (V)
2.0
2.2
2.4
2.6
050
100
150
LT1370 • G03
2.8
3.0
–25 25
75
125
Minimum Input Voltage
vs Temperature
TEMPERATURE (°C)
–50
0
SHUTDOWN DELAY (µs)
SHUTDOWN THRESHOLD (V)
2
6
8
10
20
14
0
50
75
LT1370 • G04
4
16
18
12
0
0.2
0.6
0.8
1.0
2.0
1.4
0.4
1.6
1.8
1.2
–25 25
100
125
150
SHUTDOWN THRESHOLD
SHUTDOWN DELAY
Shutdown Delay and Threshold
vs Temperature
Error Amplifier Output Current
vs Feedback Pin Voltage
FEEDBACK PIN VOLTAGE (V)
400
ERROR AMPLIFIER OUTPUT CURRENT (µA)
–300
–200
–100
300
100
–0.1 0.1
200
0
–0.3 –0.2
V
REF
–55°C
125°C
25°C
LT1370 • G06
TEMPERATURE (°C)
–50
0
MINIMUM SYNCHRONIZATION VOLTAGE (V
P-P
)
0.5
1.0
1.5
2.0
050
100
150
LT1370 • G05
2.5
3.0
–25 25
75
125
f
SYNC
= 700kHz
Minimum Synchronization
Voltage vs Temperature
Error Amplifier Transconductance
vs Temperature
TEMPERATURE (°C)
–50
0
TRANSCONDUCTANCE (µmho)
200
600
800
1000
2000
1400
0
50
75
LT1370 • G09
400
1600
1800
1200
–25 25
100
125
150
g
m
=
∆I (V
C
)
∆V (FB)
S/S Pin Input Current vs Voltage
5
LT1370
sn1370 1370fs
TYPICAL PERFORMANCE CHARACTERISTICS
U
W
TEMPERATURE (°C)
–50
FEEDBACK INPUT CURRENT (nA)
400
500
600
150
LT1370 • G11
300
200
0
0
50
100
100
800
700
–25
25
75
125
V
FB
=V
REF
Feedback Input Current
vs Temperature
TEMPERATURE (°C)
–50
–50
NEGATIVE FEEDBACK INPUT CURRENT (µA)
–30
0
0
50
75
LT1370 • G12
–40
–10
–20
–25 25
100
125
150
V
NFB
=V
NFR
Negative Feedback Input Current
vs Temperature
V
C
Pin Threshold and High
Clamp Voltage vs Temperature
TEMPERATURE (°C)
–50
1.0
V
C
VOLTAGE (V)
1.4
2.2
0
50
75
LT1370 • G10
1.2
1.8
2.0
1.6
–25 25
100
125
150
V
C
HIGH CLAMP
V
C
THRESHOLD
PIN FUNCTIONS
UUU
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: T
he 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.
6
LT1370
sn1370 1370fs
BLOCK DIAGRAM
W
OPERATION
U
The LT1370 is a current mode switcher. This means that
switch duty cycle is directly controlled by switch current
rather than by output voltage. Referring to the block
diagram, the switch is turned ON at the start of each
oscillator cycle. It is turned OFF when switch current
reaches a predetermined level. Control of output voltage is
obtained by using the output of a voltage sensing error
amplifier to set current trip level. This technique has
several advantages. First, it has immediate response to
input voltage variations, unlike voltage mode switchers
which have notoriously poor line transient response.
Second, it reduces the 90° phase shift at midfrequencies
in the energy storage inductor. This greatly simplifies
closed-loop frequency compensation under widely vary-
ing input voltage or output load conditions. Finally, it
allows simple pulse-by-pulse current limiting to provide
maximum switch protection under output overload or
short conditions. A low dropout internal regulator pro-
vides a 2.3V supply for all internal circuitry. This low
dropout design allows input voltage to vary from 2.7V to
25V with virtually no change in device performance. A
500kHz oscillator is the basic clock for all internal timing.
It turns on the output switch via the logic and driver
circuitry. Special adaptive antisat circuitry detects onset of
saturation in the power switch and adjusts driver current
instantaneously to limit switch saturation. This minimizes
driver dissipation and provides very rapid turn-off of the
switch.
A 1.245V bandgap reference biases the positive input of
the error amplifier. The negative input of the amplifier is
brought out for positive output voltage sensing. The error
amplifier has nonlinear transconductance to reduce out-
put overshoot on start-up or overload recovery. When
the feedback voltage exceeds the reference by 40mV,
error amplifier transconductance increases 10 times,
which reduces output overshoot. The feedback input also
invokes oscillator frequency shifting, which helps pro-
tect components during overload conditions. When the
feedback voltage drops below 0.6V, the oscillator fre-
quency is reduced 5:1. Lower switching frequency allows
full control of switch current limit by reducing minimum
switch duty cycle.
–
+
NFBA
NFB
S/S
FB
100k
50k
0.005Ω
–
+
EA
V
C
V
IN
GND
LT1370 • BD
GND SENSE
1.245V
REF
5:1 FREQUENCY
SHIFT
OSCSYNC
SHUTDOWN
DELAY AND RESET
LOW DROPOUT
2.3V REG
ANTI-SAT
LOGIC DRIVER
SW
SWITCH
–
+
IA
A
V
≈ 20
COMP
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16

LT1370HVCR#PBF

Mfr. #:
Buy LT1370HVCR#PBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators 500kHz Hi Eff 6A Sw Reg
Lifecycle:
New from this manufacturer.
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