MAX16920 Datasheet, PDF (11/20 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
Detailed Description
The MAX16920 power-management IC integrates three
high-voltage step-down DC-DC converters, one high-
voltage linear regulator, and an overvoltage protection
block. The three step-down converters deliver up to
150mA, 600mA, and 1.5A, while the linear regulator is
capable of up to 150mA. The MAX16920 is designed
to operate with input voltages between 5.5V to 28V and
survive voltage transients to 45V, making it ideal for
automotive applications.
The MAX16920 is optimized for high efficiency and
low standby current. The MAX16920A features 400kHz
switching frequency, while the MAX16920B features
2MHz switching frequency. The DC-DC converters can
also be synchronized to an external frequency reference
to ensure low EMI. The MAX16920 includes power-good
outputs (PG_) for DC-DC2, DC-DC3, LDOA, and a
power-on-reset (POR) output for DC-DC1. All regulators
other than DC-DC1 have an enable input (EN_).
DC-DC1
DC-DC1 is an always-on, high-efficiency, step-down
converter that outputs up to 150mA. The DC-DC1 has
a 5.5V to 28V wide input voltage range and provides
a fixed 3.3V output, or provides an adjustable output
between 1.22V to 5.5V. DC-DC1 operates in PWM mode
or in skip mode.
Soft-Start
DC-DC1 features an internal soft-start timer. The out-
put voltage soft-start ramp time is 10ms (typ) for the
MAX16920A, and 7.5ms to 8ms (typ) for the MAX16920B.
If a short circuit is encountered, after the soft-start timer
has expired, the device is disabled for 40ms (typ) (for
MAX16920A) or 28ms (typ) (for MAX16920B) and then
reattempts soft-start. This pattern repeats until the short
circuit has been removed.
Adjusting Output Voltage
DC-DC1 provides a fixed 3.3V output or an adjustable
output between 1.22V to 5.5V. Connect FB1 to GND to
set the OUT1 voltage to a fixed 3.3V voltage. Connect a
resistive divider between OUT1, FB1, and GND to adjust
the output voltage. When OUT1 is set to a voltage greater
than 3.3V, additional resistors are needed between the
converter output, OUT1 and GND. See the Setting the
Output Voltage (DC-DC1, DC-DC2, DC-DC3) section for
more information.
Overcurrent Protection
DC-DC1 limits the peak output current to 300mA
(typ). The accuracy of the current limit is ±20%,
which makes selection of external components very
easy. To protect against short-circuit events, the
MAX16920 shuts off if the current limit is exceeded
and OUT1 is below 1.5V. DC-DC1 attempts a soft-
start restart every 40ms (typ) (for MAX16920A) or
28ms (typ) (for MAX16920B) and stays off if the short
circuit has not been removed. When the short circuit is
no longer present, normal operation resumes with the
output voltage following the normal soft-start sequence.
If the MAX16920 die reaches the thermal limit of
+170˚C (typ), all outputs except OUT1 are immediately
shut off.
Power-On Reset
DC-DC1 features an open-drain reset output (POR).
If OUT1 exceeds 91.5% of its nominal output voltage,
the POR output goes high after a delay time of 5.1ms
(typ) for the MAX16920A, or 7.5ms to 8ms (typ) for the
MAX16920B. Contact the factory for other POR delay
options.
Standby and Skip Mode
When EN2, EN3, and ENA are all logic-low, the MAX16920
consumes a standby current of 25μA (typ) with no load
on OUT1. If IOUT1 < 170mA (typ), DC-DC1 operates
in skip mode. Also, the power-good outputs (PG_) are
high impedance and the undervoltage circuit is inactive
in standby mode. When any other channel (DC-DC2,
DC-DC3, or LDOA) is enabled, DC-DC1 operates in con-
stant PWM mode to improve EMI performance.
Holding Up the OUT1 During Input
Undervoltage Events
It is possible to make DC-DC1 more immune to input
voltage dropouts by adding extra capacitance buff-
ered by means of a diode on the VINA pin as shown
in Figure 1. This is useful if OUT1 powers the main
system processor, which needs to remain powered for
as long as possible. Estimate the size of the hold-up
capacitor needed on VINA using the following formula:
C_VINA = (I_IN1 x t_H)/δV
where I_IN1 is the estimated input current to DC-DC1, t_H is
the hold-up time, and ΔV is the drop-in voltage on CVINA
that can be tolerated. To prolong the hold-up time, the
LDO should be disabled during undervoltage events. If
this is not possible, the supply and load current of the
LDO should be taken into account in the calculation.
DC-DC2
DC-DC2 is a high-efficiency step-down converter that
outputs up to 600mA. DC-DC2 has a 5.5V to 28V
input voltage range and provides a fixed 5V output or
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