Check

We can check the result by using the strap widths and other chip specs to calculate the power that can be delivered. We use the procedure shown previously.

Step 1: Estimate Vcore using Ipad=50mA:

Vcore =	Vddmin(1−2× Ipad ×(Rpkg+Rbond+Rpad))   Vdd
=	1.17×(1−2×0.050×(0.022+0.02+0.04)⁄1.2
=	1.162V

Step 2: Calculate the reference power supply conductance G:

G =	7 4×r2
=	7 ⁄ (4 × 0.06) =	29.17 mhos

Step 3 is to set out the values of k_an, k_wn, k_cn and m_n for each metal layer, and use these to calculate the value of L.

metal layer 1 2 3 4 5 6  kan 100% 100% 100% 100% 180% 200% power metal allocated coefficient  kwn  70%  80% 92.5%  80% 132.5% 135% power metal used coefficient  kcn  75%¹ 100% 100% 100% 100% 300%² conductivity coefficient  mn  50%  50%  50%  50%  50%   0% core area blocked

¹75%=.06/.08; ²300%=.06/.02

From which

L =	kw1kc1(1-ps)(1-m1(1-ka2p)(1-ka3p))+
	kw2kc2(1-m2(1-ka2p)(1-ka3p))+
	kw3kc3(1-m3(1-ka2p)(1-ka3p))+
	kw4kc4(1-m4(1-ka2p)(1-ka3p))+
	kw5kc5(1-m5(1-ka2p)(1-ka3p))+
	kw6kc6(1-m6(1-ka2p)(1-ka3p))
=	( 0.20 + 0.44 + 0.50 + 0.44 + 0.72 + 4.05 )
=	6.35

Step 4: Calculate Pnom. Pnom depends on the value of Ipad which we don't know, so we start with Ipad=50mA which gives us Vcore, then Pnom and a new value of Ipad. We use a spreadsheet to iterate to the solution. The yellow squares mark user input and the pink squares are calculated values. The first estimate for Pnom is shown below.

m1′ =

m1×(1-ka2p)(1-ka3p)

Pnom=	{ (Vcore−Vmin)×Vdd2 } ×G×(kc1×ps(1−m1′)+p×L) Vddmin
=	{ (1.162‑1.1)×1.22 } ×29.2×(.75×.3×.045+.046×6.35) 1.17
=	2.226×(0.123+0.289) = 0.916W

The iteration leads to the solution of Pnom=0.921W. This is slightly higher than the 0.9W of the example, which we expect because the power strap allocation percentage has been made slightly higher by the rounding up process.