LT1370HVCR Linear Technology, LT1370HVCR Datasheet - Page 6

• Manufacturer Part Number: LT1370HVCR
• Description: IC SWTCHNG REG 6A HI-EFF 7-DD
• Manufacturer: Linear Technology
• Type: Step-Down (Buck), Step-Up (Boost), Inverting, Cuk, Flyback, Forward Converterr

Specifications of LT1370HVCR

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.25 ~ 42 V
• Current - Output: 6A
• Frequency - Switching: 500kHz
• Voltage - Input: 2.7 ~ 25 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: D²Pak, TO-263 (7 leads + tab)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

BLOCK
OPERATION
LT1370
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
6
NFB
DIAGRAM
FB
GND SENSE
U
1.245V
100k
REF
S/S
50k
W
+
–
–
+
DELAY AND RESET
SYNC
NFBA
EA
SHUTDOWN
OSC
5:1 FREQUENCY
SHIFT
LOW DROPOUT
V
2.3V REG
C
LOGIC
COMP
V
IN
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.
A
V
≈ 20
IA
+
–
DRIVER
ANTI-SAT
GND
SW
SWITCH
0.005Ω
LT1370 • BD
sn1370 1370fs