Datasheet

MAX16936
36V, 220kHz to 2.2MHz Step-Down Converter
with 28µA Quiescent Current
9Maxim Integrated
Pin Descriptions (continued)
Detailed Description
The MAX16936 is a 2.5A current-mode step-down
converter with integrated high-side and low-side MOSFETs
designed to operate with an external Schottky diode for
better efficiency. The low-side MOSFET enables fixed-
frequency forced-PWM (FPWM) operation under light-load
applications. The device operates with input voltages from
3.5V to 36V, while using only 28FA 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 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 98% duty cycle
during undervoltage transients make the device ideal for
automotive and industrial applications.
Under light-load applications, the FSYNC logic input
allows the device to either operate in skip mode for
reduced current consumption or fixed-frequency FPWM
mode to eliminate frequency variation to minimize EMI.
Fixed frequency FPWM mode is extremely useful for
power supplies designed for RF transceivers where tight
emission control is necessary. Protection features include
cycle-by-cycle current limit, overvoltage protection, and
thermal shutdown with automatic recovery. Additional
features include a power-good monitor to ease power-supply
sequencing and a 180N out-of-phase clock output relative to the
internal oscillator at SYNCOUT to create cascaded power
supplies with multiple devices.
Wide Input Voltage Range
The device includes 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 SUP and SUPSW to
drop below the programmed output voltage. Under such
conditions, the device operates 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
switching cycle. Once the off time of 25ns (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 depend-
ing on the input voltage, output-voltage, switching fre-
quency, load current, and the efficiency of the design.
The input voltage at which the devices enter dropout
PIN
NAME FUNCTION
TSSOP TQFN
10 9 EN
SUP Voltage Compatible Enable Input. Drive EN low to disable the device. Drive EN high
to enable the device.
11 10 SUP
Voltage Supply Input. SUP powers up the internal linear regulator. Bypass SUP to PGND
with a 4.7FF ceramic capacitor. It is recommended to add a placeholder for an RC filter
to reduce noise on the internal logic supply (see the Typical Application Circuit)
12 11 SUPSW
Internal High-Side Switch Supply Input. SUPSW provides power to the internal switch.
Bypass SUPSW to PGND with 0.1FF and 4.7FF ceramic capacitors.
13, 14 12, 13 LX Inductor Switching Node. Connect a Schottky diode between LX and AGND.
15 14 PGND Power Ground
16 15 PGOOD
Open-Drain, Active-Low Power-Good Output. PGOOD asserts when VOUT is above 95%
regulation point. PGOOD goes low when VOUT is below 92% regulation point.
— — EP
Exposed Pad. Connect EP to a large-area contiguous copper ground plane for effective
power dissipation. Do not use as the only IC ground connection. EP must be connected
to PGND.