
Introduction
1.10 VDD/VSS Rules And Guidelines
Samsung ASIC
1-37
STD130
The number of VDD1I/VSS1I pad pairs required for a design can be calculated from the following expression:
The number of VDD1I/VSS1I pad pairs =
where,
G = The core (excluding hard macro blocks) size in the gate counts,
S = The switching ratio (typically = 0.1),
F = Operating frequency (MHz),
Pi = Characterized current for the i-th hard macro block (mA/MHz),
Fi = Operating frequency for the i-th hard macro block (MHz),
I
em
= Current limit per V
DD
/V
SS
pad pairs based on electromigration rule. (40mA)
For reliable device operation and to minimize IR drop, no device should have fewer than 4 VDD1I/VSS1I power
pad pairs.
Extra power pad pairs may be needed for high power consuming macro blocks (SRAM, analog blocks, etc.).
1.10.3 VDD1P/VSS1P (VDD2P, 3P/VSS2P, 3P) ALLOCATION GUIDELINES.
These guidelines ensure that adequate input threshold voltage margin is maintained during I/O switching.
The number of VDD1P/VSS1P, VDD2P/VSS2P, VDD3P/VSS3P pads required for a design can be calculated from
the following expression:
In the above expression,
I
eq_p
=
∑
(Average current of input/output buffers and bi-direction pre-drivers at maximum operational I/O
frequency) [mA] (Refer to Table 1-12, Table 1-13 and Table 1-14)
0.001
0.0441 S 0.005
+
(
)
×
G F
Pi Fi
(
)
i
N_macro
∑
+
×
l
em
round up
–
Number_ of_VDD1P/VSS1P(VDD2P, 3P/VSS2P, 3P) pairs
eq_p
l
em
l
–
=
where,
N_input is the number of input buffers used,
N_output is the number of output buffers used,
N_bi is the number of bi-directional buffers used,
F is the operating frequency in MHz,
S
out
is the output mode ratio of bi-directional buffers, (typically 0.5).
I
em
= Current limit per V
DD
/V
SS
pad pairs based on electromigration rules. (40mA)
I
eq_p
I
eq_p_in
F
i
100
×
i
N_input
∑
I
j_eq_p_out
F
j
100
×
j
N_output
∑
I
k_eq_p_in
F
k
100
×
1 S
out
–
(
)
k
N_bi
∑
I
k_eq_p_out
F
k
100
×
S
out
×
+
+
+
=