RT9237 Просмотр технического описания (PDF) - Richtek Technology

Номер в каталоге

Компоненты Описание

Список матч

RT9237

Multi-Phase DC/DC Controller for CPU Core Power Supply

Richtek Technology 

Preliminary

RT9237

Design Example

Three phase converter VCORE = 1.5V, VIN = 12V, full

load current = 60Amp, droop voltage at full load =

120mV, OCP trip point for each power stage =

30Amp (at Sample/Hold), low side MOSFET RDS(ON)

= 6mΩ at room temperature, L = 2µH, COUT =

9000µF, capacitor ESR = 2m Ω.

1. Compensation setting

a. Modulator Gain, Pole and Zero

Modulator Gain =

VIN

VRAMP

, saw-tooth wave

amplitude

VRAMP

=

1V

×

56kΩ

RIMP

, choose RIRMP

= 39K, VRAMP = 1.4V, modulator Gain = 8.6 =

1

18.7dB, LC

ESR zero =

filter pole

1

2

πCRESR

=

=

2π LC

8.8kHz

= 1.2kHz

,

b. EA compensation network

Use type 2 compensation scheme (see Fig. 5),

,FZ

=

1

2πR2C1

,

mid-band gain

FP =

=

R2

R1

1

2πR2(

C1

C1

×

+

. Choose

C2

C2

R1

)

=

2.4KΩ,

R2

=

24KΩ, C1 = 6.6nF, C2 = 33pF, get FZ = 1KHz,

Fp = 200KHz, mid-band Gain=10=20dB,

modulator asymptotic Bode plot of EA

compensation and PWM loop Gain Bode

shown as Fig. 6.

C1

R2

C2

COMP

_

EA

FB

DACOUT

C3

R3

R1

VCORE

R3, C3 are used in type 3

compensation scheme (left

NC in type 2)

ROL

ROL for no load offset

setting

Fig. 5 EA Compensation Network

Asymptotic Bode Plot of PWM Loop Gain

100

80

60

Uncompensated EA Gain

40

20

0

Compensated EA Gain

-20

PWM Loop Gain

-40

Modulator Gain

-60

1100

110000

110K00

11000K00 10100000K0 1010M0000 1010000M000

Frequency (Hz)

Fig. 6 Asymptotic Bode Plot of PWM Loop Gain

2. Droop setting

Full load current of each power channel = 60A/3 =

20Amp, the ripple current = ∆IL =

5µS

×

1.5V

2µH

×

1 −



1.5V

12V





=

3.28A

, load current at S/H =

20A −

∆IL

2

= 18.36A , GM

Amp S/H

IX(MAX )

=

RDS(ON) × 18.36A

RSP

,

suggested

IX

at full = 40µA〜50µA, choose RSP = RSN = 2.7KΩ,

IX(MAX) = 40.8µA, required Droop = 120mV =

40.8µA×3×2/3×RADJ ，RADJ = 1.47KΩ.

Take the temperature rising for consideration, if

MOSFET working temperature=70°C and the

temperature coefficient =5000ppm/°C, the

RDS(ON)(70°C) = 6mΩ × {1+(70°C-27°C) ×

5000ppm/°C} = 7.3 mΩ, RADJ(70°C) = RADJ(27°C)

× {RDS(ON)(27°C)/RDS(ON)(70°C)} = 1.21KΩ

3. Over Current Protection setting

OCP trip point current = 30A (at Sample/Hold)，

IX

=

RDS(ON) × 30A

RSP

=

3

2

0.6V

× RIMAX

，RIMAX=13.6KΩ

Take the temperature rising for consideration,

RIMAX(70°C) = RIMAX(27°C) ×

{RDS(ON)(27°C)/RDS(ON)(70°C)} = 11.2KΩ

4. SS capacitor

CSS = 0.1µF is the suitable value for most

application.

DS9237-00 January 2002

www.richtek-ic.com.tw

11

Share Link: