Detailed Description
The MAX20002/MAX20003 are 2A/3A current-mode step-
down converters with integrated high-side and low-
side MOSFETs. The low-side MOSFET enables fixed-
frequency, forced-PWM operation in light-load applica-
tions. The devices operate with input voltages from 3.5V
to 36V while using only 15µA quiescent current at no
load. The switching frequency is resistor programmable
from 220kHz to 2.2MHz and can be synchronized to an
external clock. The devices’ output voltage is available
as 5V/3.3V fixed or adjustable from 1V to 10V. The wide
input voltage range, along with its ability to operate at
99% duty cycle during undervoltage transients, makes the
devices ideal for automotive applications.
In light-load applications, a logic input (FSYNC) allows
the devices to operate either in skip mode for reduced
current consumption, or fixed-frequency, forced-PWM
mode to eliminate frequency variation and help minimize
EMI. Protection features include cycle-by-cycle current
limit, and thermal shutdown with automatic recovery. See
Figure 1 for an internal block diagram.
Wide Input Voltage Range
The devices include two separate supply inputs (SUP and
SUPSW) specified for a wide 3.5V to 36V input voltage
range. V
SUP
provides power to the device and V
SUPSW
provides power to the internal switch. When the device
is operating with a 3.5V input supply, conditions such as
cold crank can cause the voltage at the SUP and SUPSW
pins to drop below the programmed output voltage. Under
such conditions, the devices operate in a high duty-cycle
mode to facilitate minimum dropout from input to output.
Maximum Duty-Cycle Operation
The devices have a maximum duty cycle of 98% (typ).
The IC monitors the off-time (time for which the low-side
FET is on) in both PWM and skip modes every switch-
ing cycle. Once the off time of 100ns (typ) is detected
continuously for 12µs, the low-side FET is forced on for
150ns (typ) every 12µs. The input voltage at which the
devices enter dropout changes depending on the input
voltage, output voltage, switching frequency, load current,
and the efficiency of the design.
The input voltage at which the devices enter dropout can
be approximated as:
OUT OUT ON_H
SUP
V (I R )
V
0.98
+×
=
Note: The previous equation does not take into account
the efficiency and switching frequency but is a good
first-order approximation. Use the R
ON_H
number from
the maximum column in the Electrical Characteristics
table.
Linear Regulator Output (BIAS)
The devices include a 5V linear regulator (V
BIAS
) that
provides power to the internal circuit blocks. Connect a
2.2µF ceramic capacitor from BIAS to AGND.
Power-Good Output (PGOOD)
The devices feature an open-drain power-good output
(PGOOD). PGOOD asserts when V
OUT
rises above 95%
of its regulation voltage. PGOOD deasserts when V
OUT
drops below 92.5% of its regulation voltage. Connect
PGOOD to BIAS with a 10kΩ resistor.
Synchronization Input (FSYNC)
FSYNC is a logic-level input useful for operating-mode
selection and frequency control. Connecting FSYNC to
BIAS or to an external clock enables fixed-frequency,
forced-PWM operation. Connecting FSYNC to AGND
enables skip-mode operation.
The external clock frequency at FSYNC can be higher
or lower than the internal clock by 20%. If the external
clock frequency is greater than 120% of the internal clock,
contact the factory applications team to verify the design.
The devices synchronize to the external clock in two
cycles. When the external clock signal at FSYNC is
absent for more than two clock cycles, the devices use
the internal clock.
System Enable (EN)
An enable control input (EN) activates the devices from
their low-power shutdown mode. EN is compatible with
inputs from automotive battery level down to 3.5V. The
high-voltage compatibility allows EN to be connected
to SUP, KEY/KL30, or the inhibit pin (INH) of a CAN
transceiver.
EN turns on the internal regulator. Once V
BIAS
is above
the internal lockout threshold, V
UVBIAS
= 3.15V (typ),
the converter activates and the output voltage ramps up
within 8ms.
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 5µA (typ). Drive EN high to bring the
devices out of shutdown.
www.maximintegrated.com
Maxim Integrated
│
12
MAX20002/MAX20003 36V, 220kHz to 2.2MHz, 2A/3A Fully
Integrated Step-Down Converters
with 15μA Operating Current
