317B 查看數據表（PDF） - Linear Technology

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317B

Micropower, 600kHz PWM DC/DC Converters

Linear Technology 

LT1317/LT1317B

APPLICATIONS INFORMATION

Table 1. Inductors Suitable for Use with the LT1317

PART

MAX

HEIGHT

VALUE DCR MFR

(mm) COMMENT

LQH3C100

10µH 0.57 Murata-Erie 2.0

Smallest Size,

Limited Current

Handling

DO1608-103 10µH 0.16 Coilcraft

3.0

CD43-100 10µH 0.18 Sumida

3.2

CD54-100 10µH 0.10 Sumida

4.5 Best Efficiency

CTX32CT-100 10µH 0.50 Coiltronics 2.2 1210 Footprint

Capacitor Selection

Low ESR (Equivalent Series Resistance) capacitors should

be used at the output of the LT1317. For most applications

a solid tantalum in a C or D case size works well. Accept-

able capacitance values range from 10µF to 330µF with

ESR falling between 0.1Ω and 0.5Ω. If component size is

an issue, tantalum capacitors in smaller case sizes can be

used but they have high ESR and output voltage ripple may

reach unacceptable levels.

Ceramic capacitors are an alternative because of their

combination of small size and low ESR. A 10µF ceramic

capacitor will work for some applications but the ex-

tremely low ESR of these capacitors may cause loop

stability problems. Compensation components will need

to be adjusted to ensure a stable system for the entire input

voltage range. Figure 4 shows a 2V to 3.3V converter with

new values for RC and CC. Figure 5 details transient

response for this circuit. Also, ceramic caps are prone to

temperature effects and the designer must check loop

stability over the operating temperature range (see section

on Frequency Compensation).

Input bypass capacitor ESR is less critical and smaller

units may be used. If the input voltage source is physically

near the VIN pin (<5mm), a 10µF ceramic or a 10µF A case

tantalum is adequate.

Diodes

Most of the application circuits on this data sheet specify

the Motorola MBR0520L surface mount Schottky diode.

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 voltage output 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.

L1

10µH

D1

VIN

VOUT

2V

3.3V

C1

10µF

VIN

SW

FB

LT1317B

SHDN

VC

GND

RC

20k

CC

1500pF

R1

1M

1%

R2

604k

1%

C2

10µF

CERAMIC

D1: MBR0520

L1: SUMIDA CD43-100

1317 F04

Figure 4. 2V to 3.3V Converter with a 10µF Ceramic Output

Capacitor. RC and CC Have Been Adjusted to Give Optimum

Transient Response.

VOUT

200mV/DIV

AC COUPLED

ILOAD

5mA TO

200mA

200µs/DIV

1317 F05

Figure 5. Transient Response for the Circuit of Figure 4.

9

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