MAX1845 Maxim, MAX1845 Datasheet - Page 22

• Manufacturer Part Number: MAX1845
• Description: Dual / High-Efficiency / Step-Down Controller with Accurate Current Limit
• Manufacturer: Maxim

Dual, High-Efficiency, Step-Down
Controller with Accurate Current Limit
Figure 8. Feedback Mux
mount all of the power components on the top side of
the board, with connecting terminals flush against one
another.
Keep the high-current paths short, especially at the
ground terminals. This practice is essential for stable,
jitter-free operation. Short power traces and load con-
nections are essential for high efficiency. Using thick
copper PC boards (2oz vs. 1oz) can enhance full-load
efficiency by 1% or more. Correctly routing PC board
traces is a difficult task that must be approached in
terms of fractions of centimeters, where a single mil-
liohm of excess trace resistance causes a measurable
efficiency penalty.
Place the current-sense resistors close to the top-side
star-ground point (where the IC ground connects to the
top-side ground plane) to minimize current-sensing
errors. Avoid additional current-sensing errors by using
a Kelvin connection from CS_ pins to the sense resis-
tors.
The following guidelines are in order of importance:
• Keep the space between the ground connection of
• Minimize the resistance on the low-side path. The
• Minimize the resistance in the high-side path. This
22
0.1V
FB1
OUT1
the current-sense resistors short and near the via to
the IC ground pin.
low-side path starts at the ground of the low-side
FET, goes through the low-side FET, through the
inductor, through the output capacitor, and returns
to the ground of the low-side FET. Minimize the resis-
tance by keeping the components close together
and the traces short and wide.
path starts at V
2V
______________________________________________________________________________________
FIXED
1.5V
FIXED
1.8V
IN
, goes through the high-side FET,
TO ERROR
AMP1
TO ERROR
AMP2
MAX1845
FIXED
2.5V
0.1V
OUT2
FB2
Figure 9. Setting V
Figure 10. PC Board Layout Example
USE AGND PLANE TO:
- BYPASS V
- TERMINATE EXTERNAL FB, ILIM,
- PIN-STRAP CONTROL
INPUTS
OVP DIVIDERS, IF USED
MAX1845
L1
VIA TO OUT1
CC
AND REF
OUT_
Q2
GND
DH_
CS_
DL_
FB_
C1
D1
Q1
OUT
AGND PLANE
VIA TO CS1
with a Resistor-Divider
C
IN
V
BATT
NOTCH
V
C
IN
IN
C
IN
AGND PLANE
TOP-SIDE GROUND PLANE
PGND PLANE
VIA TO PGND PLANE AND IC GND
Q3
C2
D2
R1
R2
USE PGND PLANE TO:
Q4
- BYPASS V
- CONNECT IC GROUND
TO TOP-SIDE STAR GROUND
VIA TO TOP-SIDE
GROUND
DD
L2
V
OUT