rt9245b Richtek Technology Corporation, rt9245b Datasheet - Page 12

• Manufacturer Part Number: rt9245b
• Description: Multi-phase Controller Core Power Supply
• Manufacturer: Richtek Technology Corporation

V
RT9245B
The differential sensing GM amplifier converts the voltage
on the sense component (can be a sense resistor or the
DCR of the inductor) to current signal into internal circuit
(see Figure 2).
Figure 3 is the test circuit for GM. We apply test signal at
GM inputs and observe its signal process output at ADJ
pin. Figure 4 shows the variation of signal processing of
all channels. We observe zero offsets and good linearity
between phases.
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12
ADJ
+
-
DCR
ADJ
L
300
250
200
150
100
50
0
1k
R
ADJ
0
SUM/M
R
Figure 3. The Test Circuit of GM
Figure 2. Current Sense Circuit
Figure 4. The Linearity of GMx
C
25
GMx
V
I
x
C
MUX
+
-
DCR
50
V
I
I
C
GM
L
x
GM
R
75
L
R
(mV)
CSN
+
-
I
X
R
+V
100
DCR
R
C
V
CSN
1k
CSN
C
C
-
125
V
C
CSN
CSPX
150
Figure 5 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
RT9245B uses an external resistor R
programmable over current trip point. OCP comparator
compares each inductor current with this reference current.
RT9245B uses hiccup mode to eliminate fault detection
of OCP or reduce output current when output is shorted
to ground.
1
2
PWM3
V
V
x
and
CSP4
CSN
V
R
IMAX
IMAX
Figure 6. Over Current Comparator
V
V
CSP4
CSN
1
3
x
OCP Comparator
I
L
R
x
Time Sharing of GM
V
CSN
DCR
IMX
Figure 5
Time (1 s/Div)
+
-
Setting
OCP
DS9245B-02 March 2007
1/3 I
1/2 I
R
IMX
X
IMAX
CH1:(2V/Div)
CH2:(50mV/Div)
CH3:(50mV/Div)
IMAX
to set a