LT1316CS8 datasheet(9/16 Pages) LINER

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LT1316

APPLICATIONS INFORMATION

4. Find IPEAK for 3.4µs on-time

IPEAK =

= 0.202A

tON(VIN – VSAT)

3.4

µs(3.3 – 0.2)

µH

5. Find RSET resistor

Overshoot =

300ns

VIN

)

300ns = 19mA

3.3

µH

)

Find RSET from Figure 3 for 0.202A – 19mA = 0.183A

RSET ≈ 13k

These discontinuous mode equations are designed to

minimize peak current at the expense of inductor size. If

smaller inductors are desired peak current must be

increased.

Capacitor Selection

Low ESR (Equivalent Series Resistance) capacitors should

be used at the output of the LT1316 to minimize output

ripple voltage. High quality input bypassing is also

required. For surface mount applications AVX TPS series

tantalum capacitors are recommended. These have been

specifically designed for switch mode power supplies and

have low ESR along with high surge current ratings.

For through-hole applications Sanyo OS-CON capacitors

offer extremely low ESR in a small package size. If peak

switch current is reduced using the RSET pin, capacitor

requirements can be eased and smaller, higher ESR units

can be used. Ordinary generic capacitors can generally be

used when peak switch current is less than 100mA,

although output voltage ripple may increase.

Diodes

Most of the application circuits on this data sheet specify

the Motorola MBR0520L surface mount Schottky diode.

This 0.5A, low drop diode suits the LT1316 well. In lower

current applications, a 1N4148 can be used although

efficiency will suffer due to the higher forward drop. This

effect is particularly noticeable at low output voltages. For

higher output voltage applications, such as LCD bias

generators, the extra drop is a small percentage of the

output voltage so the efficiency penalty is small. The low

cost of the 1N4148 makes it attractive wherever it can be

used. In through-hole applications the 1N5818 is the all

around best choice.

Lowering Output Ripple Voltage

To obtain lower output ripple voltage, a small feedforward

capacitor of about 50pF to 100pF may be placed from

VOUT to FB as detailed in Figure 6. Ripple voltages with

and without the added capacitor are pictured in Figures

7 and 8.

VIN

RSET

GND

SHDN

LT1316

µF

10k

100pF

324k

µF

CELLS

µH

VOUT

1316 F06

SHUTDOWN

Figure 6. 2-Cell to 5V Step-Up Converter

with Reduced Output Ripple Voltage

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