rt9245c Richtek Technology Corporation, rt9245c Datasheet - Page 18

• Manufacturer Part Number: rt9245c
• Description: Multi-phase Controller Core Power Supply
• Manufacturer: Richtek Technology Corporation

RT9245C
PGOOD Function
During start-up, RT9245C will detect 5V
(through DVD pin). In Figure 21, 5V
during T1. V
V
follow V
during T1. During T2, both 5V
FAULT = low, OPSS starts charging up C
of RT9245C, I
capability of OPSS) is limited and time-variant. During T2
(V1 = 0.4V > V
After V
speed of V
In Figure 20, MOSFET N1 will turn on only if V
(threshold voltage of N1)
on, V
After V
I
V
increases with higher V
is 1.4V, V
beginning of T4 and equal to about 1.1V at the end of T4.
At the end of T4, V
the range of ±40mV). An internal 1ms timer starts. After
about 1ms(T5), The open-drain output PGOOD releases.
After PGOOD releases, I
accelerate OPSS. RT9245C enters normal operation mode
and is capable to follow VID on the fly.
When any of the fault conditions happens, V
PGOOD will be pulled low immediately. If the fault condition
is one of 5V
will try to turn off both high side MOSFET and low side
MOSFET. V
typical waveform is shown in Figure 22.
www.richtek.com
18
T2
T3
T4
SS
(EAP)
TH_N1
(T4) is still equal to about 20uA. V
=
=
=
C
C
(EAP)
C
. Due to the body effect of MOSFET N1, V
is also equal to GND. V
(SS)
SS
SS
(SS)
SS
(EAP)
x
x
x
> V2, MOSFET N1 turns on, V
is still 0V.
(SS,EAP)
> V1, I
(SS)
I
(V4
(V2
OUT
CC
(SS)
SS(T2)
thus both V
I
I
V1
SS(T4)
SS(T3)
SS
becomes about 2 times faster than in T1.
low, DVD low, OC or VID_OFF, RT9245C
(SS)
-
-
will fall slowly to avoid negative V
(in Figure 20) is pulled to GND by FAULT.
V1)
V2)
(the maximal current sink and source
SS
≅
> 0), I
will be equal to about 0.7V at the
OUT
4x10
changes to about 20uA. The rising
≅
≅
1.5x10
9x10
is very close to the target (within
(EAP)
SS
(FB)
SS
4
≅
(T6) becomes about 320uA to
(T2) is equal to about 10uA.
x
. For example, if V
and V
4
0.7V = V2. Before N1 turns
C
x
4
SS
CC
C
x
(FB)
SS
C
CC
OUT
and 12V
SS
and V
or 12V
(SS,EAP)
are equal to GND
(EAP)
SS
OUT
CC
. In the design
IN
IN
starts rising.
(SS)
is not ready
is equal to
and 12V
are ready,
OUT
will try to
OUT
> V
(SS)
target
TH_N1
TH_N1
. The
and
IN
V4
V3
V2
V1
If the fault condition is OV, V
low immediately also. RT9245C will try to turn on low
side MOSFET and turn off high side MOSFET. V
fall quickly to protect CPU from high voltage. The typical
waveform is shown in Figure 23.
Figure 22. Waveform for 5V
PGOOD
T1
FAULT
V
V
V
5V
V
OUT
(SS)
OUT
DAC
CC
T2
Figure 21. Soft Start Waveform
Figure 20. Soft Start Circuit
5V
+
-
Z1
CC
T3
OPSS
_Low + DVD_Low + OC + VID_OFF
C
SS
SS
VID_OFF
T4
(SS)
CC
FB
N1
DS9245C-02 March 2007
and PGOOD will be pulled
_Low, DVD_Low, OC or
EAP
Z2
+
-
EA
T5
5V
and DVD_ready
COMP
T6
CC
_ready
OUT
PGOOD
V
V
(SS)
OUT
will