LT1310 데이터 시트보기 (PDF) - Linear Technology

부품명

상세내역

제조사

LT1310

1.5A Boost DC/DC Converter with Phase-Locked Loop

Linear Technology 

LT1310

APPLICATIO S I FOR ATIO

VOUT

100mV/DIV

AC COUPLED

IL

0.5A/DIV

RC = 3k

200µs/DIV

1310 F03a

Figure 3a. Transient Response Shows Excessive Ringing

VOUT

100mV/DIV

AC COUPLED

IL

0.5A/DIV

RC = 6k

200µs/DIV

1310 F03b

Figure 3b. Transient Response is Better

VOUT

100mV/DIV

AC COUPLED

IL

0.5A/DIV

RC = 15k

200µs/DIV

1310 F03b

Figure 3c. Transient Response is Well Damped

100mA to 200mA. Figure 3a shows the transient response

with RC equal to 3k. The phase margin is poor as evi-

denced by the excessive ringing in the output voltage and

inductor current. In Figure 3b, the value of RC is increased

to 6k, which results in a more damped response. Figure

3c shows the results when RC is increased further to 15k.

The transient response is nicely damped and the compen-

sation procedure is complete.

Compensation—Theory

Like all other current mode switching regulators, the

LT1310 needs to be compensated for stable and efficient

operation. Two feedback loops are used in the LT1310: a

fast current loop which does not require compensation,

and a slower voltage loop which does. Standard Bode plot

analysis can be used to understand and adjust the voltage

feedback loop.

As with any feedback loop, identifying the gain and phase

contribution of the various elements in the loop is critical.

Figure 4 shows the key equivalent elements of a boost

converter. Because of the fast current control loop, the

power stage of the IC, inductor and diode have been

replaced by the equivalent transconductance amplifier

gmp. gmp acts as a current source where the output current

is proportional to the VC voltage. Note that the maximum

output current of gmp is finite due to the current limit in the

IC.

From Figure 4, the DC gain, poles and zeroes can be

calculated as follows:

Output Pole: P1=

2

2 • π • RL • COUT

Error Amp Pole: P2 =

1

2 • π • RO • CC

Error Amp Zero: Z1=

1

2 • π • RC • CC

DC

Gain:

A

=

1.25

VOUT

•

gma

• RO

• gmp

• RL

In addition to the elements from Figure 4, current mode

control aslo results in some other poles and zeroes. These

are as follows:

RHP

Zero:

Z2

=

2

•

VIN2 • RL

π • VOUT2

•L

Output Zero: Z3 =

1

2 • π • ESR • COUT

Current Mode Pole: P3 > fS

3

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.

sn1310 1310fs

9

Share Link: