MAX16974 Datasheet, PDF (11/19 Pages) Maxim Integrated Products – High-Voltage, 2.2MHz, 2A Automotive Step- Down Converter with Low Operating Current

High-Voltage, 2.2MHz, 2A Automotive Step-
Down Converter with Low Operating Current
Linear Regulator Output (BIAS)
The device includes a 5V linear regulator, VBIAS, that
provides power to the internal circuitry. Connect a 1FF
ceramic capacitor from BIAS to GND. If the output
voltage is set between 3.0V and 5.6V, the internal lin-
ear regulator only provides power until the output is in
regulation. The internal linear regulator turns off once the
output is in regulation and load current is below 50mA,
allowing the output to provide power to the device.
External Clock Input (FSYNC)
The device synchronizes to an external clock signal
applied at FSYNC. The signal at FSYNC must have a
10% shorter period than the internal clock period for
proper synchronization. The internal clock signal takes
over if the externally applied signal has a frequency
lower than the internal clock frequency.
Adjustable Reset Level
The device features a programmable reset threshold
using a resistive divider between OUT, RESETI, and
GND. Connect RESETI to GND for the internal threshold.
RES asserts low when the output voltage falls to 85% of
its programmed level. RES deasserts when the output
voltage goes above 90% of its set voltage.
Some microprocessors have a wide input voltage range
(5V to 3.3V) and can operate during device dropout. Use
a resistive divider at RESETI to adjust the reset activation
level (RES goes low) to lower levels. The reference volt-
age at RESETI is 1.2V (typ).
The device also offers a capacitor-programmable reset
timeout period. Connect a capacitor from CRES to GND
to adjust the reset timeout period. When the output volt-
age goes out of regulation, RES asserts low, and the
reset timing capacitor discharges with a 1mA pulldown
current. Once the output is back in regulation, the reset
timing capacitor recharges with 10FA (typ) current. RES
stays low until the voltage at CRES reaches 1.25V (typ).
Dropout Operation
The device has an effective maximum duty cycle to help
refresh the BST capacitor when continuously operated
in dropout. When the high-side switch is on for three
consecutive clock cycles, the device forces the high-
side switch off during the final 35% of the fourth clock
cycle. When the high-side switch is off, the LX node
is pulled low by current flowing through the external
Schottky diode. This increases the voltage across the
BST capacitor. To ensure that the inductor has enough
current to pull LX to ground, an internal load sinks cur-
rent from VOUT when the device is close to dropout and
when the external load is small. Once the input voltage
is increased above the dropout region, the device con-
tinues to regulate without restarting.
If the device has neither external clock nor external load,
the effective maximum duty cycle is 92% when operating
deep into dropout. This effective maximum duty cycle is
influenced by the external load and by the external syn-
chronized clock, if any.
System Enable (EN)
An enable-control input (EN) activates the device from its
low-power shutdown mode. EN is compatible with inputs
from automotive battery level down to 3.3V. The high-
voltage compatibility allows EN to be connected to SUP,
KEY/KL30, or the INH pin of a CAN transceiver.
EN turns on the internal regulator. Once VBIAS is above
the internal lockout level, VUVL = 3.05V (typ), the con-
troller activates and the output voltage ramps up within
2048 cycles of the switching frequency.
A logic-low at EN shuts down the device. During shut-
down, the internal linear regulator and gate drivers turn
off. Shutdown is the lowest power state and reduces the
quiescent current to 5FA (typ). Drive EN high to bring the
device out of shutdown.
Overvoltage Protection
The device includes an overvoltage protection
circuit that protects the device when there is an over-
voltage condition at the output. If the output voltage
increases by more than 10% of its set voltage, the device
stops switching. The device resumes regulation once the
overvoltage condition is removed.
Overload Protection
The overload protection circuitry is activated when the
device is in current limit and VOUT is below the reset
threshold. Under these conditions the device enters a
soft-start mode. If the overcurrent condition is removed
before the soft-start mode is over, the device regulates
the output voltage to its set value. Otherwise, the soft-
start cycle repeats until the overcurrent condition is
removed.
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