RT9245A View Datasheet(PDF) - Richtek Technology

Part Name

Description

View to exact match

RT9245A

Multi-Phase PWM Controller for CPU Core Power Supply

Richtek Technology 

RT9245A

1. Compensation Setting

a. Modulator Gain, Pole and Zero :

From the following formula:

Modulator Gain = VIN/VRAMP = 12/1.9 = 6.3 (i.e 16dB)

where VRAMP : Ramp amplitude of saw-tooth wave

LC Filter Pole = 3.88kHz and

ESR Zero = 28kHz

b. EA Compensation Network :

Select RB1 = 1.5k, RB2 = 15k, C1 = 2.7nF, C2 = 5.6pF,

C3 = 680pF and use the Type 3 compensation scheme

shown in Figure 28. By calculation.

FZ1 =

2π

1

x RB1 x C3

= 156kHz

FZ2

=

2π

x

1

RB2

x

C1

=

3.9kHz

FP

=

2π

1

x RB2 x

(C2//C1)

=

5.8kHz

Middle Band Gain = 10 (i.e. 20dB)

C3 680pF

RB1

1.5k

C2 5.6pF

RB2 C1

15k 2.7nF

-

+EA

Figure 28. Type 3 compensation network of EA

The over all loop gain with load is shown in Figure 29 to

Figure 31.

3. Over-Current Protection Setting

Consider the temperature coefficient of copper

3900ppm/°C,

1

2

×

VIMAX

RIMAX

⇔

1

3

×

IL

× DCR

R CSN

1

2

×

1V

RIMAX

⇔

1

3

×

40A

× 1.39m

330Ω

Ω

⇒ RIMAX = 8.9kΩ

4. Soft-Start Capacitor Selection

For most application cases, 0.1µF is a good engineering

value.

DS9245A-05 March 2007

Figure 29. The Frequency Response with No Load

www.richtek.com

21

Share Link: