Detailed Description

The MAX25232 family of small, current-mode-controlled buck converters features synchronous rectification and requires

no external compensation network. The devices are designed for 3A output current and can stay in dropout by running

at 99% duty cycle. Each device provides an accurate output voltage of ±2% in FPWM mode within the 6V to 18V

input range. Voltage quality can be monitored by observing the PGOOD signal. The devices operate at 2.1MHz (typ)

frequency, which allows for small external components, reduced output ripple, and guarantees no AM band interference.

The devices are also available at 400kHz (typ) for minimum switching losses and maximum efficiency.

Each device features an ultra-low 3.5μA (typ) quiescent supply current in standby mode. The device enters standby

mode automatically at light loads if the high-side FET (HSFET) does not turn on for eight consecutive clock cycles.

The devices operate from a 3.5V to 36V supply voltage and can tolerate transients up to 40V, making them ideal for

automotive applications. The devices are available in factory-trimmed output voltages (5V, 3.3V). MAX25232ATCF and

MAX25232ATCG configuration can be used to program output voltage between 3V and 10V using an external resistor-

divider. For fixed-output voltages outside of 3.3V and 5V, contact factory for availability.

Enable Input (EN)

Each device 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 the overall quiescent supply current. To realize a programmable undervoltage-lockout level,

use a resistor-divider from SUP to EN to AGND.

Bias/UVLO

Each device features undervoltage lockout. When the device is enabled, an internal bias generator turns on. LX begins

Soft-Start

Each device features an internal soft-start timer. The output voltage soft-start time is 3.5ms (typ), which includes the delay

in PGOOD. If a short circuit or undervoltage is encountered after the soft-start timer has expired, the device is disabled

for 7ms (typ) and then reattempts soft-start again. This pattern repeats until the short circuit has been removed.

Oscillator/Synchronization and Efficiency (SYNC)

Each device has an on-chip oscillator that provides a 2.1MHz (typ) or 400kHz (typ) switching frequency. There are two

operation modes, depending on the condition of SYNC. If SYNC is unconnected or at AGND, the device operates in

highly efficient pulse-skipping mode. If SYNC is connected to BIAS or has a clock applied to it, the device is in forced-

PWM mode (FPWM). The device can be switched during operation between FPWM mode and skip mode by switching

SYNC.

Skip-Mode Operation

The devices enter skip mode when the SYNC pin is connected to ground or is unconnected and the peak load current

is < 600mA (typ). In this mode, the HSFET is turned on until the inductor current ramps up to 600mA (typ) peak value

and the internal feedback voltage is above the regulation voltage (1.0V, typ). At this point, both the HSFETs and low-side

FETs (LSFETs) are turned off. Depending on the choice of the output capacitor and the load current, the HSFET turns

on when OUT (valley) drops below the 1.0V (typ) feedback voltage. When the device is in skip mode, the internal high-

Achieving High Efficiency at Light Loads

Each device operates with very low-quiescent current at light loads to enhance efficiency and conserve battery life. When

the device enters skip mode, the output current is monitored to adjust the quiescent current. The lowest quiescent-current

standby mode is only available for factory-trimmed devices between 3.0V and 5.5V output voltages. When the output

current is < approximately 5mA, the device operates in the lowest quiescent-current mode, also called standby mode. In

MAX25232

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