MAX15158 datasheet(18/28 Pages) MAXIM

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Compensation Design Guidelines

MAX15158/MAX15158A utilizes a fixed-frequency, peak

current-mode control scheme to provide easy compensation

and fast transient response. It is by nature for boost or

inverting-buck-boost converters to have a right half plane

(RHP) zero in their small signal control-to-output transfer

function. For boost converters, the location of RHP zero

is calculated by:

fRHP = VOUT x (1 - D)2 / (2 x π x IOUT(MAX) x L)

where:

IOUT(MAX) = Maximum load current per phase

D = Duty cycle = 1 - VIN/VOUT

L = Value of the inductor

For inverting-buck-boost converters, the location of RHP

zero is calculated by:

fRHP = VOUT x (1 - D)2 / (2 x π x IOUT(MAX) x L x D)

where:

D = Duty cycle = VOUT/(|VIN| + VOUT)

For stable operation, it is required that the bandwidth

of control loop (BW) is sufficiently lower than fRHP and

switching frequency (fSW).

BW ≤ Minimum(fRHP/7, fSW/10)

A type-II compensation network is required to be

connected between COMP and GND (RCOMP, CCOMP

and CPAR in Figure 4) to provide sufficient phase margin

and gain margin to the control loop. The value of the

compensation network can be selected by:

RCOMP = 16 x π x BW x RSENSE x COUT x VOUT/

[N x (1 - D) x GMEA x VREF]

CCOMP = 5/(π x RCOMP x BW)

CPAR = 1/(2 x π x RCOMP x fSW)

where,

RSENSE = Value of the sense resistor

COUT = Value of the output capacitor

N = Number of phases

GMEA = Error Amplifier Transconductance (1.1mS, typ)

Figure 4. Peak-Current-Mode Control Loop

COMP

RAMP

GENERATOR

RAMP

PWM

COMPARATOR

CSP_

CSN_

PHASE CURRENT

IMBALANCE

PWM

CONTROL

LOGIC

CLOCK

GND

MAX15158 /

MAX15158A

GND

TYPE-II COMPENSATION

RSENSE

DH_

DL_

ERROR

AMPLIFIER

VSLOPE = 1.9 × IRAMP × RRAMP

GND

RRAMP

IRAMP

VCS_ = 8.3 × (VCSP_ - VCSN_)

LOW-

SIDE

MOSFET

VIN

HIGH-

SIDE

MOSFET

VOUT*

CCOMP RCCOMP

CPAR

*FOR BOOST APPLICATIONS VOUT IS REFERRED TO GND; FOR INVERTING-BUCK-BOOST

APPLICATIONS VOUT IS REFERRED TO VIN

∑

GND

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MAX15158/MAX15158A

High-Voltage Multiphase Boost Controller

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