16

Maximum Current Limit Setpoint

Therefore,

Therefore, the range of load currents that will cause the

internal current sense comparator to detect an overload

condition through a 3mΩ embedded PCB trace is: 14.2A <

ICL 60A, with 28.6A being the nominal overload condition.

Design Rules for Using a Droop Resistor

The basic equation for laying an embedded resistor is:

or R = ρ ×

where:

A= W × t = cross-sectional area

ρ= the copper resistivity (µΩ - mil)

L= length (mils)

W = width (mils)

t = thickness (mils)

For most PCBs the copper thickness, t, is 35µm (1.37 mils)

for one ounce copper. ρ = 717.86µΩ-mil

create a 43mV drop at full load is:

=

= 3.0mΩ

The resistivity of the copper will drift with the temperature

according to the following guidelines:

Droop Resistor Width Calculations

The droop resistor must have the ability to handle the load

current and therefore requires a minimum width which is

calculated as follows (assume one ounce copper thickness):

43mV

14.2A

43mV

L

(W × t)

L

A

Application Information: continued

COMP

IRL3103S

12V

5V

1.2µH

GATE(H)

GATE(L)

PGnd

1200µF/10V x 3

1µF

SS

LGnd

330pF

0.1µF

1200µF

10V x 5

CS5166

PWRGD

3.0mΩ

1000pF

510

3.3K

0.1µF

0.1µF

COMP

IRL3103S

12V

5V

1.2µH

GATE(H)

GATE(L)

PGnd

1200µF/10V x 3

1µF

SS

LGnd

330pF

CS5166

3.0mΩ

1000pF

510

3.3K

0.1µF

0.1µF

PWRGD

2.8V/30A

Power

Supply

IRL3103S

IRL3103S

Figure 23: Current sharing of a 2.8V/30A power supply using two CS5166 synchronous buck regulators.