LT3471 datasheet(11/16 Pages) LINER

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LT3471

3471fb

APPLICATIONS INFORMATION

Figure 7. Bode Plot of 3.3V to 7V Application

From Figure 6, the DC gain, poles and zeroes can be

calculated as follows:

Output Pole: P1=

2• π •RL •COUT

Error Amp Pole: P2=

2• π •RO •CC

Error Amp Zero: Z1=

2• π •RC •CC

DC GAIN: A=

VREF

VOUT

•gma •RO •gmp •RL •

ESR Zero: Z2=

2• π •RESR •COUT

RHP Zero: Z3=

VIN

2 •R

2• π •VOUT

2 •L

High Frequency Pole: P3>

Phase Lead Zero: Z4=

2• π •R1• CPL

Phase Lead Pole: P4=

2• π •CPL •

R1•R2

R1+R2

The Current Mode zero is a right half plane zero which can

be an issue in feedback control design, but is manageable

with proper external component selection.

Using the circuit of Figure 2 as an example, Table 3 shows

the parameters used to generate the Bode plot shown in

Figure 7.

Table 3. Bode Plot Parameters

Parameter

Value

Units

Comment

Application Speciﬁc

COUT

4.7

μF

Application Speciﬁc

RESR

mΩ

Application Speciﬁc

0.9

MΩ

Not Adjustable

CPL

Adjustable

kΩ

Not Adjustable

90.9

kΩ

Adjustable

kΩ

Adjustable

VOUT

Application Speciﬁc

VIN

3.3

Application Speciﬁc

gma

μmho

Not Adjustable

gmp

9.3

mho

Not Adjustable

2.2

μH

Application Speciﬁc

1.2

MHz

Not Adjustable

From Figure 7, the phase is –115° when the gain reaches

0dB giving a phase margin of 65°. This is more than

adequate. The crossover frequency is 50kHz.

FREQUENCY (Hz)

–10

–20

100

10k

100k

3471 F07

–30

–350

–50

–100

–250

–150

–200

–300

–400

GAIN

PHASE

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