4

LT3436

3436fa

TYPICAL PERFOR A CE CHARACTERISTICS

GND (Pins 1, 5, 6, 8, 9, 16, 17): Short GND pins 1, 5, 6,8,

9, 16 and the exposed pad (pin 17) on the PCB. The GND

is the reference for the regulated output, so load regulation

will suffer if the “ground” end of the load is not at the same

voltage as the GND of the IC. This condition occurs when

the load current flows through the metal path between the

GND pins and the load ground point. Keep the ground path

short between the GND pins and the load and use a ground

plane when possible. Keep the path between the input

bypass and the GND pins short. The exposed pad should

be attached to a large copper area to improve thermal

performance.

internal regulator. Keep the external bypass capacitor

close to this pin.

SW (Pins 3, 4): The switch pin is the collector of the on-

chip power NPN 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.

SHDN (Pin 11): The shutdown pin is used to turn off the

regulator and to reduce input drain current to a few

microamperes. The 1.35V threshold can function as an

accurate undervoltage lockout (UVLO), preventing the

regulator from operating until the input voltage has reached

a predetermined level. Float or pull high to put the regula-

tor in the operating mode.

FB (Pin 12): The feedback pin is used to set output voltage

using an external voltage divider that generates 1.2V at the

pin with the desired output voltage. If required, the current

limit can be reduced during start up when the FB pin is

below 0.5V (see the Current Limit Foldback graph in the

Typical Performance Characteristics section). An imped-

ance of less than 5k

Ω at the FB pin is needed for this

feature to operate.

and the input of the peak switch current comparator. It is

normally used for frequency compensation, but can do

double duty as a current clamp or control loop override.

This pin sits at about 0.3V for very light loads and 0.9V at

maximum load.

SYNC (Pin 14): The sync pin is used to synchronize the

internal oscillator to an external signal. It is directly logic

compatible and can be driven with any signal between

20% and 80% duty cycle. The synchronizing range is

equal to

initial operating frequency, up to 1.4MHz. See

Synchronization section in Applications Information for

details. When not in use, this pin should be grounded.

SHDN Supply Current

Input Supply Current

Current Limit Foldback

SHDN VOLTAGE (V)

0

300

250

200

150

100

50

0

0.6

1.0

3436 G07

0.2

0.4

0.8

1.2

1.4

INPUT VOLTAGE (V)

0

1200

1000

800

600

400

200

0

5

10

15

20

3436 G08

25

30

FEEDBACK VOLTAGE (V)

0

0.2

0.4

0.8

0.6

1.0

1.2

3436 G09

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

40

30

20

10

0

MINIMUM

INPUT

VOLTAGE

SWITCH CURRENT