MAX16903SAUE View Datasheet(PDF) - Maxim Integrated
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MAX16903SAUE Datasheet PDF : 15 Pages
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MAX16903
2.1MHz, High-Voltage,
1A Mini-Buck Converter
Detailed Description
The MAX16903 is a small, current-mode buck convert-
er that features synchronous rectification and requires
no external compensation network. The MAX16903 is
designed for 1A output current. The MAX16903 can stay
in dropout by running at 97% duty cycle. It provides an
accurate output voltage within the input range of +6.5V to
+18V. Voltage quality can be monitored by observing the
PGOOD signal. The MAX16903 operates at 2.1MHz (typ)
frequency, which allows for small external components,
reduced output ripple, and guarantees no AM band inter-
ference.
The MAX16903 features an ultra-low 25μA (typ) quiescent
supply current in standby mode. Standby mode is entered
when load currents are below 5mA and when SYNC
is low. The MAX16903 operates from a +3.5V to +28V
supply voltage and tolerates transients up to +42V,
making it ideal for automotive applications. The MAX16903
is available in factory-trimmed output voltages from 1.8V
to 10.7V in 100mV steps. Contact factory for availability
of voltage options.
Enable (EN)
The MAX16903 is activated by driving EN high. EN
is compatible from a +3.3V logic level to automotive
battery levels. EN can be controlled by microcontrollers
and automotive KEY or CAN inhibit signals. The EN input
has no internal pullup/pulldown current to minimize over-
all quiescent supply current. To realize a programmable
undervoltage lockout level, use a resistor-divider from
SUP to EN to GND.
BIAS/UVLO
The MAX16903 features undervoltage lockout. When the
device is enabled, an internal bias generator turns on. LX
begins switching after VBIAS has exceeded the internal
undervoltage lockout level VUVLO = 3V (typ).
Soft-Start
The MAX16903 features an internal soft-start timer. The
output voltage soft-start ramp time is 8ms (typ). If a short
circuit or undervoltage is encountered, after the soft-start
timer has expired, the device is disabled for 30ms (typ)
and it reattempts soft-start again. This pattern repeats
until the short circuit has been removed.
Oscillator/Synchronization and
Efficiency (SYNC)
The MAX16903 has an on-chip oscillator that provides a
switching frequency of 2.1MHz (typ). Depending on the
condition of SYNC, two operation modes exist. If SYNC is
unconnected or at GND, the device must operate in highly
efficient pulse-skipping mode if the load current is below
the SKIP mode current threshold. If SYNC is at BIAS or
has a frequency applied to it, the device is in forced PWM
mode. The MAX16903 offers the best of both worlds. The
device can be switched during operation between forced
PWM mode and SKIP mode by switching SYNC.
SKIP Mode Operation
SKIP mode is entered when the SYNC pin is connected
to ground or is unconnected and the peak load current
is < 350mA (typ). In this mode, the high-side FET is
turned on until the current in the inductor is ramped up
to 350mA (typ) peak value and the internal feedback
voltage is above the regulation voltage (1.2V typ). At this
point, both the high-side and low-side FETs are turned
off. Depending on the choice of the output capacitor and
the load current the high-side FET turns on when OUTS
(valley) drops below the 1.2V (typ) feedback voltage.
Achieving High Efficiency at Light Loads
The MAX16903 operates with very low quiescent current
at light loads to enhance efficiency and conserve battery
life. When the MAX16903 enters SKIP mode the output
current is monitored to adjust the quiescent current.
When the output current is < 5mA, the MAX16903 oper-
ates in the lowest quiescent current mode also called the
standby mode. In this mode, the majority of the internal
circuitry (excluding that necessary to maintain regulation)
in the MAX16903, including the internal high-voltage
LDO, is turned off to save current. Under no load and with
SKIP mode enabled, the IC draws only 25μA (typ) current.
For load currents > 5mA, the IC enters normal SKIP mode
still maintaining very high efficiency.
Controlled EMI with Forced-Fixed Frequency
In forced PWM mode, the MAX16903 attempts to operate
at a constant switching frequency for all load currents. For
tightest frequency control, apply the operating frequency
to SYNC. The advantage of this mode is a constant
switching frequency, which improves EMI performance;
the disadvantage is that considerable current can be
thrown away. If the load current during a switching cycle
is less than the current flowing through the inductor, the
excess current is diverted to GND. With no external load
present, the operating current is in the 10mA range.
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