ir3084a International Rectifier Corp., ir3084a Datasheet - Page 34

• Manufacturer Part Number: ir3084a
• Description: Xphase Tm Vr 10/11 Control Ic
• Manufacturer: International Rectifier Corp.

DESIGN EXAMPLE: VRM 11 7íPHASE CONVERTER
SPECIFICATIONS
Input Voltage: V
DAC Voltage: V
No Load Output Voltage Offset: V
Output Current: I
Maximum Output Current: I
Load Line Slope: R
VRM11 Startup Boot Voltage = 1.100V
Soft Start Time: TD2 = 1.1ms
VCC Ready to VCC Power Good Delay: TD5 = 1.0ms
Over Current Delay: T
Dynamic VID Negative Slew Rate: SR
Over Temperature Threshold: T
POWER STAGE
Phase Number: n = 7
Switching Frequency: f
Output Inductors: L = 220 nH, R
Output Capacitors: C = 560uF, R
IR3084A EXTERNAL COMPONENTS
Oscillator Resistor Rosc
The switching frequency sets the value of R
the switching frequency of 400kHz per phase requires R
VDAC Slew Rate Programming Capacitor C
From Figure 17 on page 23, the sink current of the VDAC pin at 400kHz (R
VDAC slew-rate programming capacitor from the specified negative slew rate using Equation (1).
Calculate the VDAC compensation resistor from Equation (2);
From Figure 17 on page 23, the source current of the VDAC pin is 90uA at R
slew rate is can be calculated using Equation (3);
Page 34 of 45
C
R
SR
VDAC
VDAC
UP
=
=
=
DAC
I
O
= 12V
I
0.5
C
SR
SOURCE
= 130 ADC
O
I
VDAC
= 1.3V
SINK
= 1.20 m
DOWN
+
OCDEL
SW
3.2*10
=400 kHz
C
=
VDAC
OMAX
=
90*10
33*10
= 250µs
2
5 .
−
2
PCB
L
15
C
80
= 150 ADC
*
= 0.60 m
O_NLOFST
= 7m
10
=
−
−
= 115 ºC
*
6
9
0.5
10
−
DOWN
=
3
/
−
2.7mV/uS
10
+
6
(33*10
= 15mV
−
= 2.5mV/us
OSC
3.2*10
6
VDAC
=
32
as shown by the curve in Figure 13 on page 23. In this design,
−
0 .
and Resistor R
−
9
15
nF
)
2
= 10
OSC
=
,
3.5
to be 30.1k .
Choose C
VDAC
VDAC
OSC
OSC
= 33nF
= 30.1K . The VDAC positive
=30.1k
IR3084A
10/30/2006