rt9246a Richtek Technology Corporation, rt9246a Datasheet - Page 11

• Manufacturer Part Number: rt9246a
• Description: Multi-phase Controller Core Power Supply
• Manufacturer: Richtek Technology Corporation

Droop and Load Line Setting
RT9246A
resistor R
current-dependent voltage V
V
reference voltage at non-inverting input of the error amplifier
as
calculated as:
DS9246A-04 March 2007
Load
V
Figure 4. The
ADJ
V
ADJ
PWM
I
I
CORE
CORE
CORE
shown if Figure 6.
V
V
Figure 5.
SS
SS
is then subtracted form VID_DAC output as the real
=
Line
I 8
X
ADJ
injects averaged phase current
R
(5A/Div)
(1V/Div)
=
ADJ
ΔV
Over Current Protection at steady state
ΔI
connected to ADJ pin to generate a load-
Over Current Protection in the soft start
CORE
CORE
Over Current Protection
Over Current Protection
=
Consequently, load line slope is
8
Time (2.5ms/Div)
Time (5ms/Div)
interval
N
x
R
x
ADJ
ADJ
R
COMM
x
for droop setting:
R
LX
(500mV/Div)
(10A/Div)
I
(5V/Div)
(2V/Div)
X
into the
where N is the phase number of operation.
The averaged current
R
Voltage at IOUT pin V
and is calculated as:
Output Voltage Offset Function
RT9246A provides programmable initial offset function.
External resistor R
generate offset current
, where V
through R
hold the inverting pin equal to V
offset voltage is consequently added to V
Current Ratio Setting
Current ratio adjustment is possible as described below.
It is important for achieving thermal balance in practical
application where thermal conditions between phases are
not identical. Figure 7 shows the application circuit of GM
for current ratio requirement. According to Basic Circuit
Theory, if
V
V
IOUT
IOUT
CORE
V =
R
L
X
LX
X
connected to IOUT pin for monitoring load current.
=
= (R // R ) x C then
=
R +R
I 8
V
Figure 6. Load Line and Offset Function
V
CORE
SX
VOSS
FB1
R
X
DAC
SX
PX
x
as shown in Figure 6. Error amplifier would
R
PX
−
is 1V typical. One quarter of I
IOUT
V
PX
x I x R
DAC
ADJ
VOSS
I
VOSS
=
LX
R
FB1
+
8
IOUT
I
X
4
I
4
I x
and voltage source at VOSS pin
X
VOSS
is also injected into the resistor
x
LX
CORE
R
is proportional to load current
R
N
FB1
VOSS
x
=
R
x
R
R
COMM
V
V
DAC
ADJ
VOSS
VOSS
ADJ
+
-
RT9246A
Error
Amp.
− V
x
R
R
www.richtek.com
ADJ
LX
ADJ
DAC
. A constant
I 8
VOSS
− V
X
ADJ
flows
as :
11