RT9245PC datasheet(12/22 Pages) RICHTEK

12 / 22 page

RT9245

DS9245-06

March 2007

www.richtek.com

Figure 2 is the test circuit for GM. We apply test signal at

GM inputs and observe its signal process output at ADJ

pin. Figure 3 shows the variation of signal processing of

all channels. We observe zero offsets and good linearity

between phases.

Figure 3. The Linearity of GMx

Figure 4 shows the time sharing technique of GM amplifier.

We apply test signal at phase 4 and observe the waveforms

at both pins of GM amplifier. The waveforms show time

sharing mechanism and the perfomance of GM to hold

both input pins equal when the shared time is on.

Over Current Protection

RT9245 uses an external resistor RIMAX to set a

programmable over current trip point. OCP comparator

compares each inductor current with this reference current.

RT9245 uses hiccup mode to eliminate fault detection of

OCP or reduce output current when output is shorted to

ground.

Figure 5. Over Current Comparator

Figure 6. The Over Current Protection in the soft start

interval

1/3 IX

1/2 IIMAX

OCP Comparator

COMMON

IMAX

DCR

⇔

100

150

200

250

300

100

125

150

Vx (mV)

CH1:(5V/Div)

CH2:(5V/Div)

Over Current Protection

Time (25ms/Div)

PWM

VSS

Figure 2. The Test Circuit of GM

DCR

ESR

RCSN

GMx

VCSP

VCSN

Figure 4

Time Sharing of GM

Time (1

μs/Div)

PWM3

VCSP4

and

VCSN

CH1:(2V/Div)

CH2:(50mV/Div)

CH3:(50mV/Div)

VCSP4

VCSN

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