10

LT1310

1310f

APPLICATIO S I FOR ATIO

Using the circuit of Figure 1 as an example, the following

table shows the parameters used to generate the Bode plot

shown in Figure 5.

Table 4. Bode Plot Parameters

PARAMETER

VALUE

UNITS

COMMENT

30

Ω

Application Specific

4.7

µF

Application Specific

2M

Ω

Not Adjustable

820

pF

Adjustable

15

k

Ω

Adjustable

12

V

Application Specific

5

V

Application Specific

500

µmho

Not Adjustable

1.5

mho

Not Adjustable

L

5.6

µH

Application Specific

1.6

MHz

Adjustable

ESR

10

m

Ω

Not Adjustable

From Figure 5, the phase is 120

° when the gain reaches

0dB giving a phase margin of 60

°. This is more than

adequate. The crossover frequency is 50kHz, which is

about three times lower than the frequency of the right half

plane zero Z2. It is important that the crossover frequency

be at least three times lower than the frequency of the RHP

zero to achieve adequate phase margin.

–

+

R2

R1, R2: FEEDBACK RESISTOR DIVIDER NETWORK

1310 F04

R1

FB

1.255V

REFERENCE

Figure 4. Boost Converter Equivalent Model

Diode Selection

A Schottky diode is recommended for use with the LT1310.

The Microsemi UPS120 is a very good choice. Where the

input to output voltage differential exceeds 20V, use the

UPS140 (a 40V diode). These diodes are rated to handle an

average forward current of 1A. For applications where the

average forward current of the diode is less than 0.5A, an

ON Semiconductor MBR0520 diode can be used.

Setting Output Voltage

To set the output voltage, select the values of R1 and R2

(see Figure 1) according to the following equation:

RR

V

V

OUT

12

1 255

1

=









.

–

A good range for R2 is from 5k to 30k.

FREQUENCY (Hz)

0

50

100

100

10k

100k

1M

1310 F05a

–50

1k

FREQUENCY (Hz)

–100

0

100

10k

100k

1M

1946 F05b

–200

–180

1k

60

°

Figure 5. Bode Plot of Figure 1’s Circuit