LT1616 datasheet(9/28 Pages) LINER

9 / 28 page

LT1766/LT1766-5

1766fa

should be used if resistors are increased beyond the

suggested values and short-circuit conditions occur with

high input voltage. High frequency pickup will increase

and the protection accorded by frequency and current

foldback will decrease.

CHOOSING THE INDUCTOR

For most applications, the output inductor will fall into the

range of 15

µH to 100µH. Lower values are chosen to

reduce physical size of the inductor. Higher values allow

more output current because they reduce peak current

seen by the LT1766 switch, which has a 1.5A limit. Higher

values also reduce output ripple voltage.

When choosing an inductor you will need to consider

output ripple voltage, maximum load current, peak induc-

tor current and fault current in the inductor. In addition,

other factors such as core and copper losses, allowable

component height, EMI, saturation and cost should also

be considered. The following procedure is suggested as a

way of handling these somewhat complicated and con-

flicting requirements.

Output Ripple Voltage

Figure 3 shows a typical output ripple voltage waveform

for the LT1766. Ripple voltage is determined by ripple

current (ILP-P) through the inductor and the high

frequency impedance of the output capacitor. The follow-

ing equations will help in choosing the required inductor

APPLICATIO S I FOR ATIO

value to achieve a desirable output ripple voltage level. If

output ripple voltage is of less importance, the subse-

quent suggestions in Peak Inductor and Fault Current

and EMI will additionally help in the selection of the

inductor value.

Peak-to-peak output ripple voltage is the sum of a triwave

(created by peak-to-peak ripple current (ILP-P) times ESR)

and a square wave (created by parasitic inductance (ESL)

and ripple current slew rate). Capacitive reactance is

assumed to be small compared to ESR or ESL.

ESR

ESL

RIPPLE

LP P

()( )+()

Figure 2. Frequency and Current Limit Foldback

–

1.2V

BUFFER

VSW

GND

TO SYNC CIRCUIT

1766 F02

TO FREQUENCY

SHIFTING

OUTPUT

ERROR

AMPLIFIER

1.4V

LT1766

Figure 3. LT1766 Ripple Voltage Waveform

2.5

µs/DIV

40mV/DIV

VOUT AT IOUT = 1A

VOUT AT IOUT = 0.1A

INDUCTOR CURRENT

AT IOUT = 1A

INDUCTOR CURRENT

AT IOUT = 0.1A

0.5A/DIV

VIN = 40V

VOUT = 5V

L = 47

µH

C = 100

µF, 10V, 0.1Ω

1766 F03

LT1616 Datasheet(PDF) 9 Page - Linear Technology

LT1616 Datasheet(HTML) 9 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

Datasheet Download

Link URL