
RC5037
PRODUCT SPECIFICATION
10
P
top and bottom signal layers of the PCB, it is not recom-
mended to use these layers to route the high current portions
of the regulator design. Since it is more common to use 1 oz.
copper on the PCB inner layers, it is recommended to use
those layers to route the high current paths in the design.
Power and Ground Connections
The connection of VCCA to the 5V power supply plane
should be short and bypassed with a 0.1
m
F directly at the
VCCA pin of the RC5037. The ideal connection would be a
via down to the 5V power plane. A similar arrangement
should be made for the VCCP pin that connects to +12V.
Each ground should have a separate via connection to the
ground plane below.
A 12V power supply is used to bias the VCCP. A 47
W
resistor is used to limit the transient current into VCCP.
A 1uF capacitor filter is used to filter the VCCP supply and
source the transient current required to charge the MOSFET
gate capacitance. This method provides sufficiently high gate
bias voltage to the MOSFET (V
GS
), and therefore reduces
R
DS(ON)
of the MOSFET and its power loss.
Figure 12 provides about 5V of gate bias which works well
when using typical logic-level MOSFETs, as shown in
Figure 13. Non-logic-level MOSFETs should not be used
because of their higher R
DS(ON)
.
MOSFET Gate Bias
Figure 12. 12V Gate Bias Configuration
VI/O
+5V
VCCP
47
Q1
L2
RSENSE
CBULK
D1
1
μ
F
GNDP
+12V
65-5037-12
Figure 11. Examples of good and poor layouts
5
6
7
8
5
= "Quiet" Pins
65-5037-10
6
7
4
3
2
8
1
4
3
2
1
Example of
a Good Layout
Example of
a Problem Layout
Noisy signal radiates
onto quiet pins and the
trace is too long.
Gate resistor is far away
from the MOSFET.
Noisy signal is routed
away from quiet pins and the
trace length is kept under 0.5in.
The gate resistor is as close
as possible to the MOSFET.
Figure 13. R
DS(ON)
vs. V
GS
for Selected Logic-Level MOSFETs
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
1.5
2
2.5
3
3.5
4
5
6
7
8
9
10
11
V
GS
R
D
2SK1388
NDP7060
NDP706A
NDP706AEL