Datasheet

LT1618
4
sn1618 1618fas
PIN FUNCTIONS
UUU
FB (Pin 1/Pin 1): Feedback Pin. Set the output voltage by
selecting values for R1 and R2 (see Figure 1):
RR
V
V
OUT
12
1 263
1=
.
ISN (Pin 2/Pin 2): Current Sense (–) Pin. The inverting
input to the current sense amplifier.
ISP (Pin 3/Pin 3): Current Sense (+) Pin. The noninverting
input to the current sense amplifier.
I
ADJ
(Pin 4/Pin 4): Current Sense Adjust Pin. A DC voltage
applied to this pin will reduce the current sense voltage. If
this adjustment is not needed, tie this pin to ground.
GND (Pin 5/Pin 5): Ground Pin. Tie this pin directly to local
ground plane.
NC (Pin 6/NA): No Connection for MS Package.
SW (NA/Pin 6): Switch Pin for DD Package. Connect this
pin to Pin 7.
SW (Pin 7/Pin 7): Switch Pin. This is the collector of the
internal NPN power switch. Minimize the metal trace area
connected to this pin to minimize EMI.
V
IN
(Pin 8/Pin 8): Input Supply Pin. Bypass this pin with
a capacitor to ground as close to the device as possible.
SHDN (Pin 9/Pin 9): Shutdown Pin. Tie this pin higher
than 1V to turn on the LT1618; tie below 0.3V to turn it off.
V
C
(Pin 10/Pin 10): Compensation Pin for Error Amplifier.
Connect a series RC from this pin to ground. Typical values
are 2k and 10nF.
Exposed Pad (NA/Pin 11): The Exposed Pad on the DD
package is GND and must be soldered to the PCB GND for
optimum thermal performance.
TYPICAL PERFOR A CE CHARACTERISTICS
UW
TEMPERATURE (°C)
–50
SWITCHING FREQUENCY (MHz)
125
1618 G07
0
75
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
–25 25 50
100
V
IN
= 18V
V
IN
= 1.6V
FEEDBACK PIN VOLTAGE (V)
SWITCHING FREQUENCY (MHz)
1.2
1618 G08
0 0.2
0.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0.4 0.6
1.0
T
J
= 25°C
SHUTDOWN PIN VOLTAGE (V)
0
SHDN PIN CURRENT (µA)
20
1618 G09
5
10
15
50
45
40
35
30
25
20
15
10
5
0
T
J
= –50°C
T
J
= 25°C
T
J
= 125°C
Switching Frequency Frequency Foldback SHDN Pin Current
(MS/DD)