MAX17497A 查看數據表（PDF） - Maxim Integrated

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MAX17497A

AC-DC and DC-DC Peak Current-Mode Converters with Integrated Step-Down Regulator

Maxim Integrated 

MAX17497A/MAX17497B

AC-DC and DC-DC Peak Current-Mode Converters

with Integrated Step-Down Regulator

value of the input inductor taking into account tolerance where:

and saturation effects. fSWMIN is the minimum switch-

ing frequency for the MAX17497B from the Electrical

Characteristics section.

= ∆ILIN

VOUTF



×

DMAX × (1−

LIN × fSW

D

MAX

)





for DMAX

<

0.5

Output-Capacitor Selection

X7R ceramic output capacitors are preferred in industrial

applications due to their stability over temperature. The = ∆ILIN

output capacitor is usually sized to support a step load

0.25



×

VOUTF

 LIN × fSW







for

DMAX

≥

0.5

of 50% of the maximum output current in the application,

such that the output-voltage deviation is contained to 3%

of the output-voltage change. The output capacitance

can be calculated as:

Error-Amplifier Compensation Design

The loop-compensation values for the error amplifier can

now be calculated as:

COUTF

=

ISTEP × tRESPONSE

∆VOUTF

RZ

=

90

×

VOUTF 2 × COUTF ×

IOUTF × LIN

(1−

D MAX )

t RESPONSE

≅

(0.33

fC

+

1

fSW

)

where DMAX is the duty cycle at the lowest operating input

voltage and IOUTF_MAX is the maximum load current:

where ISTEP is the load step, tRESPONSE is the response

time of the controller, DVOUTF is the allowable output-

voltage deviation, and fC is the target closed-loop

crossover frequency. fC is chosen as 1/10 the switch-

ing frequency (fSW). For the boost converter, the output

capacitor supplies the load current when the main switch

is on, and therefore the output-voltage ripple is a function

of duty cycle and load current. Use the following equa-

tion to calculate the output-capacitor ripple:

∆VCOUTF

= IOUTF × DMAX

COUTF × fSW

Input-Capacitor Selection

The input ceramic capacitor value required can be

calculated based on the ripple allowed on the input DC

bus. The input capacitor should be sized based on the

RMS value of the AC current handled by it. The calcula-

tions are as:

CINF

=

VINMIN3×.7f5SW× I×O(U1T−FDMAX



)

CZ

=

VOUTF × COUTF

2 × IOUTF × RZ

CP

=

π

×

1

fSW

×RZ

Slope-Compensation Ramp

The slope required to stabilize the converter at duty

cycles greater than 50% can be calculated as:

SE

=

0.41 ×

(VOUTF

LIN

−

VINMIN)

V per µs

where LIN is in FH.

Output Diode Selection

The design procedure for output diode selection is identi-

cal to that outlined in the DCM Boost section.

The input-capacitor RMS current can be calculated as:

ICIN_RMS

=

∆ILIN

2× 3

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