rt9246a Richtek Technology Corporation, rt9246a Datasheet - Page 13

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

Referring to Figure 13, I
where I
RT9246A could sense the valley current, right hand side
of Equation (1) should always be positive:
Since R
could be simplified as:
For example, assuming the negative inductor valley current
is −5A at no load, then for
DS9246A-04 March 2007
I =
V
R
V
R
X
1.31
1.29
1.28
1.27
1.26
1.25
1.24
1.23
OUT
CSN
OUT
CSN
1.3
Load Line without dead zone at light loads
V
R
LX_V
CSN
OUT
CSN
+
0
≥
I
Figure13. Application circuit
w/i Dead Zone Compensation
LX_V
GMx
is the valley of inductor current. To make sure
>> R
+
I
Ix
LX_V
R
R
I
CSN
x R
LX_V
+
-
COMM
COMM
x R
5
R
I
LX
LX
CSN
x R
LX
+
R
in practical application, Equation (2)
R
LX
CSN
Figure 12
X
I
CSN
R
LX_V
R
LX
COMM
is expressed as:
+
10
R
X
w/o Dead Zone Compensation
= 82k
COMM
I
I
x R
OUT
LX_V
R
R
CSN
COMM
+
LX
(A)
x R
R
open
C
15
V
LX
≥
X
X
LX
-
0
of GM
V
20
OUT
25
(1)
(2)
R
R
Choose R
Figure 12 shows that dead zone of load line at light load
is eliminated by applying this technique.
Error Amplifier Characteristic
For fast response of converter to meet stringent output
current transient response, RT9246A provides large slew
rate capability and high gain-bandwidth performance.
Figure 14. EA Rising
COMM
CSN
V
V
1.3V
R
Figure 15. EA
COMP
COMP
V
V
CSN
FB
FB
≤ 85.8kΩ
= 330Ω, R
≥
CSN
-5A 1m
500mV/Div)
(2V/Div)
(500mV/Div)
(2V/Div)
330
= 82kΩ
×
Ω
Falling Transient with 10pF Loading;
ADJ
Slew Rate=8V/us
Ω
EA
EA
= 160Ω, V
Transient with 10pF Loading; Slew
Rate=8V/us
Time (250ns/Div)
Time (250ns/Div)
Falling Slew Rate
Rising Slew Rate
OUT
= 1.300V
RT9246A
www.richtek.com
13