MAX16920 Datasheet, PDF (17/20 Pages) Maxim Integrated Products – Automotive Power-Management IC with Three Step-Down Converters and Linear Regulator

Automotive Power-Management IC with
Three Step-Down Converters and Linear Regulator
5) Route high-speed switching nodes (BST_ and LX_)
away from sensitive analog areas (SYNC and FB_)
and keep their area as small as possible.
6) Place the VINA, VINB, and VL bypass capacitors as
close as possible to the device. If using multiple
bypass capacitors, place the lowest value capacitor
closest to the pin. The ground connection of the VL
bypass capacitor should be connected directly to the
GND pin with a wide trace.
7) Keep any feedback traces as short and small as
possible to prevent noise pickup. Make feedback
connections directly to the positive terminal of the
output capacitor to ensure good regulation.
Thermal Considerations
The power dissipation of the MAX16920 is made up of
three components: power dissipation due to the DC-DC
converters, power dissipation due to the linear regulator,
and internal power dissipation. The DC-DC converter
power dissipation can be estimated as follows:
PDCDC = PRESISTIVE + PSWITCHING
PRESISTIVE = D x IOUT2 x RH + (1 - D) x IOUT2 x
RL
where D is the duty cycle (approximately VOUT/VIN),
IOUT is the output current, RH is the resistance of
the high-side switch, and R_L is the resistance of the
low-side switch.
PSWITCHING = fSW x (0.25 x VIN x IOUT x tRISE + 0.25 x
VIN x IOUT x tFALL)
where V_IN is the input voltage, t_RISE is the rise time of
the LX node (approximately 5ms (MAX16920B) and
10ms (MAX16920A)), and tFALL is the fall time of the
LX node (approximately 5ms (MAX16920B) and 10ms
(MAX16920A)).
The linear regulator power dissipation is:
PLIN = (VIN - 5V) x ILIN
The internal power dissipation can be approximately
calculated as VIN_ x 35mA during normal operation. In
many applications, the power dissipation of the linear
regulator (LDOA) is a large contributor to the overall
power dissipation. Note that although the linear regula-
tor can provide up to 150mA of output current, in most
cases the permitted output current is lower due to power
dissipation limitations.
The total power dissipation leads to an increase in the
chip temperature, which is dependent on the thermal
resistance of the board upon which the MAX16920 is
mounted. The maximum permitted junction temperature
is +150°C and a junction temperature above this eventu-
ally leads to overtemperature shutdown of the chip.
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