Datasheet

5
LT1371
TYPICAL PERFORMANCE CHARACTERISTICS
U
W
TEMPERATURE (°C)
–50
FEEDBACK INPUT CURRENT (nA)
400
500
600
150
LT1371 • 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
LT1371 • 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
0.4
V
C
PIN VOLTAGE (V)
0.6
1.0
1.2
1.4
2.4
1.8
0
50
75
LT1371 • G10
0.8
2.0
2.2
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.
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. Load
on the FB pin should not exceed 250µA when NFB pin is
used. See Applications Information.
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 (R and T7 Packages Only): Shutdown and Synchroni-
zation Pin. The S/S pin is logic level compatible. Shutdown
is active low and the shutdown threshold is typically 1.3V.
For normal operation, 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.
SHDN: (SW Package Only): The Shutdown pin is active
low and the shutdown threshold is typically 1.3V. For
normal operation, pull the SHDN pin high, tie it to V
IN
or
leave it floating.
SYNC (SW Package Only): To synchronize switching,
drive the SYNC pin between 600kHz and 800kHz. If not
used, the SYNC pin can be tied high, low or left floating.
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.