LM5177DCPR datasheet(44/60 Pages) TI2

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The compensation zero can be placed at 1.5 times the boost output pole frequency. Keep in mind that this

locates the zero at three times the buck output pole frequency, which results in approximately 30 degrees of

phase loss before crossover of the buck loop and 15 degrees of phase loss at intermediate frequencies for the

boost loop:

fZC= 1.8 kHz

(44)

The compensation gain resistor, Rc1, is calculated with:

RC1= 2π×fbw

gmEA ×RFB1+RFB2

RFB2 ×ACS×RCS×COUT

1−DMAX × 11+fbwfRHP2=1.9 kΩ

(45)

where

• DMAX is the maximum duty cycle at the minimum VIN in boost mode.

• ACS is the current sense amplifier gain.

The compensation capacitor, Cc1, is then calculated from:

CC1= 1

2π×fZC× Rc1= 45.8nF

(46)

The standard values of compensation components are selected to be Rc1 = 1.91 kΩ and Cc1 = 47 nF.

A high frequency pole (fpc2) is placed using a capacitor (Cc2) in parallel with Rc1 and Cc1. Set the frequency of

this pole at seven to ten times of fbw to provide attenuation of switching ripple and noise on COMP while avoiding

excessive phase loss at the crossover frequency. For a target fpc2 = 6 kHz, Cc2 is calculated using Equation 47:

CC2= 1

2π×fpc2×Rc1= 1.68 nF

(47)

Select a standard value of 1.8 nF for Cc2. These values provide a good starting point for the compensation

design. Each design must be tuned in the lab to achieve the desired balance between stability margin across the

operating range and transient response time.

8.2.2.13 External Component Selection

Table 8-3. Components Example for Typical Application

Reference

Description

Part Number

RCOMP

1.91kΩ

CCOMP1

47nF, 50V Ceramic Capacitor

CCOMP2

1.8nF, 50V Ceramic Capacitor

CSS

18nF, 50V Ceramic Capacitor or 20nF, 80V Ceramic

Capacitor

GCM21B5C1H183JA16 or

GCM21B5C1K203JA16

RFB,top

71.5kΩ

RFB,bot

4.7kΩ

RnFLT

10kΩ

RIMONOUT

82kΩ

CIN1

2× 10µF, 50V Ceramic Capacitor

GCM32EC71H106KA03

CIN2

1× 100μF, 63V Aluminum Capacitor

PCR1J101MCL1GS

N-Channel 40V MOSFET, RDS(on) = 4.3mΩ

SQJ422EP

N-Channel 40V MOSFET, RDS(on) = 4.3mΩ

SQJ422EP

N-Channel 40V MOSFET, RDS(on) = 4.3mΩ

SQJ422EP

N-Channel 40V MOSFET, RDS(on) = 4.3mΩ

SQJ422EP

RCS

1.00mΩ

3xKRL2012E-C-R003-F

LM5177

SNVSBU4F – JUNE 2022 – REVISED JANUARY 2025

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