5
LT1424-9
sn14249 14249fs
PGND (Pin 5): Power Ground. This pin is the emitter of the
power switch device and has large currents flowing through
it. It should be connected directly to a good quality ground
plane.
V
SW
(Pin 6): This is the collector node of the output switch
and has large currents flowing through it. Keep the traces
to the switching components as short as possible to
minimize electromagnetic radiation and voltage spikes.
V
IN
(Pin 7): Supply Voltage. Bypass input supply pin with
10µF or more. The part goes into undervoltage lockout
when V
IN
drops below 2.8V. Undervoltage lockout stops
switching and pulls the V
C
pin low.
R
CCOMP
(Pin 8): Pin for the External Filter Capacitor for
Load Compensation Function. A common 0.1µF
ceramic capacitor will suffice.
PIN FUNCTIONS
UUU
SHDN (Pin 1): Shutdown. This pin is used to turn off the
regulator and reduce V
IN
input current to a few tens of
microamperes. The SHDN pin can be left floating when
unused.
V
C
(Pin 2): Control Voltage. This pin is the output of the
feedback amplifier and the input of the current compara-
tor. Frequency compensation of the overall loop is effected
by placing a capacitor between this node and ground.
SYNC (Pin 3): Pin to synchronize internal oscillator to
external frequency reference. It is directly logic compat-
ible and can be driven with any signal between 10% and
90% duty cycle. If unused, this pin should be tied to
ground.
SGND (Pin 4): Signal Ground. This pin is a clean ground.
The internal reference and feedback amplifier are referred
to it. Keep the ground path connection to the V
C
compen-
sation capacitor free of large ground currents.
Minimum Flyback Enable Time
vs Temperature
Minimum Switch On Time
vs Temperature
Flyback Enable Delay Time
vs Temperature
TEMPERATURE (°C)
–50
200
225
275
25 75
1424-9 G10
175
150
–25 0
50 100 125
125
100
250
SWITCH ON TIME (ns)
TEMPERATURE (°C)
–50
200
225
250
25 75
1424-9 G11
175
150
–25 0
50 100 125
125
100
75
ENABLE DELAY TIME (ns)
TEMPERATURE (°C)
–50
200
225
275
25 75
1424-9 G12
175
150
–25 0
50 100 125
125
100
250
ENABLE TIME (ns)
TYPICAL PERFOR A CE CHARACTERISTICS
UW
