Datasheet

Automotive Power-Management IC with
Three Step-Down Converters and Linear Regulator
MAX16920
16
Setting the Undervoltage Output
(UVO) Level
The UVO level is set by using two resistors connected
between the input (before the reverse-polarity protection
diode if used) and the UVI and between UVI and UVS.
The UVS switch has a 1540Ω typical resistance that
must be taken into account when calculating the external
resistor values to maintain accuracy. Use the following
equation to calculate the value of the upper resistor, R1:
R1 = (V
BT
– 1.205)/(1.205/(R2 + R
UVS
))
where V
BT
is the desired undervoltage level at the
battery, and R2 is the value of the lower resistor (a good
starting value is 100kΩ). R
UVS
is 1540Ω. See the typical
operating circuits in Figures 4 and 5.
PCB Layout Guidelines
Grounding
Establish a “quiet” ground for all analog ground (GND)
connections. Sources of switching current and other
noisy signals should be connected to their respective
power grounds (PGNDA and PGNDB). GND, PGNDA,
and PGNDB should be connected together at the GND
pin of the MAX16920. If needed, use multiple vias to
connect ground planes between different board layers
to keep the ground impedance low.
The following should be connected to analog GND:
1) The GND pin of the MAX16920.
2) The ground connection of the V
L
capacitor.
3) The grounds for any feedback resistor-dividers used.
4) The ground side of the OUTA output capacitor.
All other ground connections should be to their respec-
tive PGNDA and PGNDB grounds.
General Guidelines
1) Minimize the area of high-current loops by placing
each DC-DC converter’s inductor and output capaci-
tors near its input capacitors and its LX_ and PGND_
pins. OUT1 and OUT2 converters share PGNDB for
ground return, while OUT3 has PGNDA for ground
return.
2) Keep the power traces and load connections as
short and wide as possible, especially at the ground
terminals. This practice is essential for high efficiency
and jitter-free operation.
3) Use thick copper PCBs (2oz. vs. 1oz.) if possible to
enhance efficiency.
4) Keep the LX_ connections short and wide and place
the inductors as close as possible to the associated
LX pin.
Figure 3. Typical Application Circuit for Setting OUT1 or OUT3 Above 3.3V
Ri1 = 212kI
Ri2 = 121kI
FBi
V
FB_
= 1.21V
~750mV
USE INTERNAL
R1 = 100kI
OUT1/OUT3
DC-DC3 OUTPUT
7.4V
FB1/FB3
R2 = 50kI
R
TOP
R
BOT