ADP3164 Analog Devices, ADP3164 Datasheet - Page 10

• Manufacturer Part Number: ADP3164
• Description: 5-Bit Programmable 4-Phase Synchronous Buck Controller
• Manufacturer: Analog Devices

ADP3164
R
The value of R
current. The current comparator of the ADP3164 has a mini-
mum current limit threshold of 143 mV. Note that the 143 mV
value cannot be used for the maximum specified nominal cur-
rent, as headroom is needed for ripple current and tolerances.
The current comparator threshold sets the peak of the inductor
current yielding a maximum output current, I
twice the peak inductor current value less half of the peak-to-
peak inductor ripple current. From this, the maximum value of
R
In this case, 5 mΩ was chosen as the closest standard value.
Once R
where current limit is reached, I
the maximum current sense threshold of 173 mV:
At output voltages below 750 mV, the current sense threshold is
reduced to 108 mV, and the ripple current is negligible. There-
fore, at dead short the output current is reduced to:
To safely carry the current under maximum load conditions, the
sense resistor must have a power rating of at least:
where:
In this formula, n is the number of phases, and η is the con-
verter efficiency, in this case assumed to be 85%. Combining
Equations 6 and 7 yields:
Output Resistance
This design requires that the regulator output voltage measured
at the CPU drop when the output current increases. The speci-
fied voltage drop corresponds to a dc output resistance of:
SENSE
SENSE
R
OUT
R
I
I
I
P
I
OUT CL
OUT CL
OUT SC
SENSE RMS
R
SENSE
is calculated as:
SENSE
SENSE
=
P
(
(
(
R
V
(
SENSE
=
ONL
≤
)
)
)
has been chosen, the output current at the point
= ×
= ×
= ×
I
SENSE
SENSE RMS
I
I
)
n
=
n
4
n
O
O
2
−
V
∆
V
80
=
+
CSCL MIN
OFL
V
173
V
4
R
(
I
is based on the maximum required output
I
5
CSCL MAX
CS SC
O
n
A
SENSE
L RIPPLE
R
2
(
(
m
(
2
SENSE
=
mV
)
×
2
Ω
2
×
(
1 4605
)
×
η
.
0 85 12
)
V
= ×
.
1 475
R
×
−
OUT
)
4
.
V
SENSE
)
4 10 8
=
IN
OUT(CL)
−
×
×
V
108
80
80
n I
V
5
2
−
4
×
V
143
.
m
1 3845
A
A
mV
.
Ω
, can be calculated using
L RIPPLE
×
+
A
(
2
5
mV
10 8
=
=
m
116 8
.
V
2
86 4
Ω
O
)
, which equals
A
=
=
.
.
1 2
0 95
=
A
.
.
A
5 6
W
.
m
m
Ω
Ω
(5)
(6)
(7)
(3)
(4)
(8)
The required dc output resistance can be achieved by terminating
the g
tion resistance that will yield the correct dc output resistance:
where n
the g
transconductance of the g
of phases.
Output Offset
Intel’s VRM 9.1 specification requires that at no load the nominal
output voltage of the regulator be offset to a lower value than the
nominal voltage corresponding to the VID code to make sure that
circuit tolerances never cause the output voltage to exceed the
VID value. The offset is introduced by realizing the total termina-
tion resistance of the g
the REF pin and ground. The resistive divider introduces an
offset to the output of the g
through the gain of the g
voltage near its allowed maximum at light load. Furthermore, the
output of the g
At no load, the current sense threshold is increased by the peak of
the ripple current in the inductor and reduced by the delay between
sensing when the current threshold has been reached and when
the high side MOSFET actually turns off. These two factors are
combined with the inherent voltage (V
g
The divider resistors (R
can now be calculated, assuming that the internal resistance of
the g
Choosing the nearest 1% resistor value gives R
Finally, R
Choosing the nearest 1% resistor value gives R
R
R
R
m
B
B
A
V
V
R
n t
amplifier that commands a current sense threshold of 0 mV:
4 60
=
=
=
GNL
GNL
T
×
m
m
m
×
V
3
R
=
1
REF
V
amplifier with a resistor. The value of the total termina-
amplifier (R
D
amplifier to the PWM comparator CMP1, g
T
I
7 48
=
=
n
×
−
.
is the division ratio from the output voltage signal of
−
R
n
V
1
A
ns
−
×
1 074
T
I
R
R
V
GNL
V
.
is calculated:
g
×
SENSE
k
OGM
×
GNL
1
1
m
Ω
+
R
m
5
0
×
10 8
V
SENSE
m
amplifier sets the current sense threshold voltage.
+
−
−
R
V
Ω ×
−
.
g
×
OUT
I
REF
R
OGM
m
2 2
1
L RIPPLE
n
B
.
(
×
A
I
m
12 5 1 074
(
=
mmho
V
=
×
) is 1 MΩ:
amplifier with a divider connected between
A
ONL
.
m
7 48
5
3
4 2 2
2
for the upper and R
.
m
V
stage, accurately positions the output
m
=
×
m
)
−
1
amplifier itself, and n is the number
×
×
Ω ×
V
amplifier that, when reflected back
k
2
( .
.
.
VID
1 4605
R
Ω
12 5 5
SENSE
12 5
mmho
−
)
.
1
V
.
M
×
1
1
V
−
×
Ω
GNL0
−
×
12
m
n
1 475
−
0 95
I
.
Ω
10 5
.
V
−
), at the output of the
600
.
V
−
1
V
m
B
IN
1 475
k
)
B
A
Ω
Ω
.
nH
for the lower)
=
−
= 10.5 kΩ.
= 26.7 kΩ.
L
10 37
=
=
V
26 7
OUT
7 48
.
V
.
m
.
×
k
is the
k
×
Ω
k
Ω
Ω
(12)
(10)
(11)
(9)