ISL6277A Datasheet, PDF (22/38 Pages) Intersil Corporation – Multiphase PWM Regulator for AMD Fusion Mobile CPUs Using SVI 2.0

ISL6277A
TABLE 3. COMP & COMP_NB OUTPUT VOLTAGE OFFSET
SELECTION
RESISTOR VALUE [kΩ]
1%
COMP
COMP_NB
MIN
TOLERANCE
MAX
V_{CORE OFFSET} OFFSET
TOLERANCE VALUE TOLERANCE
[mV]
[mV]
5.54
5.62
5.70
-43.75
18.75
7.76
7.87
7.98
-37.5
31.25
11.33
11.5
11.67
-31.25
43.76
16.65
16.9
17.15
-25
50
19.3
19.6
19.89
-18.75
37.5
24.53
24.9
25.27
-12.5
25
33.49
34.0
34.51
-6.25
12.5
40.58
41.2
41.81
6.25
0
51.52
52.3
53.08
18.75
18.75
72.10
73.2
74.29
31.25
31.25
93.87
95.3
96.72
43.76
43.76
119.19
121
122.81
50
50
151.69
154
156.31
37.5
37.5
179.27
182
184.73
25
25
206.85
210
213.15
12.5
12.5
OPEN
0
0
Floating DriverX & PWM_Y Configuration
The ISL6277A allows for one internal driver and one PWM output
to be configured to opposite VRs depending on the desired
configuration of the Northbridge VR. Internal DriverX can be used
as Channel 1 of the Northbridge VR with PWM_Y used for
Channel 3 of the Core VR. Using this partitioning, a 2+1 or 1+1
configured ISL6277A would not require an external driver.
If routing of the driver signals would be a cause of concern due to
having an internal driver on the Northbridge VR, then the
ISL6277A can be configured to use PWM_Y as Channel 1 on the
Northbridge VR. DriverX would then be used as Channel 3 of the
Core VR. This allows the placement of the external drivers for the
Northbridge VR to be closer to the output stage(s) depending on
the number of active Phases, providing placement and layout
flexibility to the Northbridge VR.
The floating internal driver and PWM output are configured
based on the programming resistor from FCCM_NB to GND. The
FCCM_NB programming resistor value also sets the slew rate and
switching frequency of the Core and Northbridge VRs. These
features are outlined in the following sections. Table 4 shows
which resistor values sets the configuration and slew rate for the
ISL6377. The resistor value shown in the table must be used and
the resistor tolerance must be 1%. The MIN and MAX tolerance
around each resistor value is the same as Table 3 and provides
margin to insure the 1% tolerance resistor will be read correctly.
TABLE 4. FCCM_NB RESISTOR SELECTION
RESISTOR VALUE
[kΩ]
SLEW RATE FOR CORE
AND NORTHBRIDGE
[mV/µs]
DriverX
PWM_Y
5.62
20
7.87
15
11.5
12.5
16.9
19.6
10
Core VR NB VR
20
Channel 3 Channel 1
24.9
15
34.0
12.5
41.2
10
52.3
20
73.2
15
95.3
12.5
121
10
NB VR Core VR
154
20
Channel 1 Channel 3
182
15
210
12.5
OPEN
10
VID-on-the-Fly Slew Rate Selection
The FCCM_NB resistor is also used to select the slew rate for VID
changes commanded by the processor. Once selected, the slew
rate is locked in during soft-start and is not adjustable during
operation. The lowest slew rate which can be selected is
10mV/µs which is above the minimum of 7.5mV/µs required by
the SVI2 specification. The slew rate selected sets the slew rate
for both Core and Northbridge VRs; they cannot be independently
selected.
CCM Switching Frequency
The Core and Northbridge VR switching frequency is set by the
programming resistors on COMP_NB and FCCM_NC. When the
ISL6277A is in continuous conduction mode (CCM), the switching
frequency is not absolutely constant due to the nature of the R³â„¢
modulator. As explained in “Multiphase R3™ Modulator” on
page 15, the effective switching frequency increases during load
insertion and decreases during load release to achieve fast
response. Thus, the switching frequency is relatively constant at
steady state. Variation is expected when the power stage
condition, such as input voltage, output voltage, load, etc.
changes. The variation is usually less than 10% and does not
have any significant effect on output voltage ripple magnitude.
Table 5 defines the switching frequency based on the resistor
values used to program the COMP_NB and FCCM_NB pins. Use
the previous tables related to COMP_NB and FCCM_NB to
determine the correct resistor value in these ranges to program
the desired output offset, Slew Rate and DriverX/PWM_Y
configuration.
22
FN8322.0
December 19, 2012