MB39C011APFT-G-BND-ERE1 Datasheet, PDF(27/53 Page) Cypress Semiconductor – 2 ch DC/DC Converter IC with Synchronous Rectification

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MB39C011APFT-G-BND-ERE1 Datasheet, PDF (27/53 Pages) Cypress Semiconductor – 2 ch DC/DC Converter IC with Synchronous Rectification

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MB39C011A

R3 ï

fLC ï´ï R1

2 ï´ï fESR ï fLC

R3, Rc

C1, Cc

fLC

: [ï]

: [F]

: Resonant frequency [Hz] of the coil L [H] and output

capacitor C [F]

C1 ï

ï°ï ï´ï fLC (R1 ï« R3)

fLC ï½ 2 ï´ï ï°ïL ï´ï C

fESR : Resonant frequency [Hz] of the output capacitor C [F] and ESR

[ï]

Rc ï

Cc ï

(R1//R3) ï´ï fESR ï´ï fCO

VIN ï´ï fLC2

2 ï´ï ï°ï ï´ï RC ï´ï fLC

fESR ï½

2 ï´ï ï°ï ï´ï ESR ï´ï C

fCO

R1//R3

VIN

: Crossover frequency (arbitrary setting) [Hz]

: Resistance of R1 and R3 connected in parallel [ï]

: Switching system power supply voltage [V]

14.2 Notes on Phase Compensation Circuit Constants

Select the constants of the following three points and select the constant for the design of the phase compensation circuit when

the large load sudden change, or the capacitor is connected to DC/DC converter operating.

In particular, if a capacitance much larger than the output capacitance of the DC/DC converter is connected by hard-switching

while the DC/DC converter is operating, the output voltage may begin vibrating or the protection function may be activated, due

to the sudden response. Note the following points.

14.2.1 Error Amp output (FB1 and FB2 pins) current capacity

The resistance constants of the phase compensation circuit need to be designed by considering the current capacities of the Error

Amp outputs (FB1 and FB2 pins (pins 6 and 11)). Take the output source current

( ï 300 ïA Max) of the Error Amp and the threshold voltage VT100 (1.7 V Typ) of the PWM Comp into consideration, select the

resistance values such that the following formula is satisfied.

300 [ïA] >

1.7 [V]

R1//R2//R3 ï« RC

R1//R2//R3 ï½ Resistance of R1, R2 and R3 connected in parallel [ï]

RC : [ï]

Although low resistance values may be desired to improve the noise immunity, the above formula may not be satisfied as a result.

While it is ideal for each of the resistance values to satisfy the above formula, in this situation the values may be used after

confirming that there are no problems when used under the rapidly varying load conditions.

14.2.2 Phase Margin at the Output Load changes

Select phase compensation constants that ensure the phase margin when the output load (resistive load, capacitative load,

inductive load) is connected.

Document Number: 002-08369 Rev. *A

Page 27 of 53

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