MAX15046 Datasheet, PDF(10/23 Page) Maxim Integrated Products – 40V, High-Performance, Synchronous Buck Controller

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40V, High-Performance, Synchronous

Buck Controller

Detailed Description

The MAX15046 synchronous step-down controller oper-

ates from a 4.5V to 40V input-voltage range and gener-

ates an adjustable output voltage from 85% of the input-

voltage down to 0.6V while supporting loads up to 25A.

As long as the device supply voltage is within 5.0V to

5.5V, the input power bus (VIN) can be as low as 3.3V.

The MAX15046 offers adjustable switching frequency

from 100kHz to 1MHz with an external resistor. The

adjustable switching frequency provides design flex-

ibility in selecting passive components. The MAX15046

adopts an adaptive synchronous rectification to elimi-

nate external freewheeling Schottky diodes and improve

efficiency. The device utilizes the on-resistance of the

external low-side MOSFET as a current-sense element.

The current-limit threshold voltage is resistor-adjustable

from 30mV to 300mV and is temperature-compensated,

so that the effects of the MOSFET RDS(ON) variation

over temperature are reduced. This current-sensing

scheme protects the external components from damage

during output overloaded conditions or output short-

circuit faults without requiring a current-sense resistor.

Hiccup-mode current limit reduces power dissipation

during short-circuit conditions. The MAX15046 includes

a power-good output and an enable input with precise

turn-on/-off threshold to be used for monitoring and for

power sequencing.

The MAX15046 features internal digital soft-start that

allows prebias startup without discharging the output. The

digital soft-start function employs sink current limiting to

prevent the regulator from sinking excessive current when

the prebias voltage exceeds the programmed steady-

state regulation level. The digital soft-start feature prevents

the synchronous rectifier MOSFET and the body diode of

the high-side MOSFET from experiencing dangerous lev-

els of current while the regulator is sinking current from the

output. The MAX15046 shuts down at a +150NC junction

temperature to prevent damage to the device.

DC-DC PWM Controller

The MAX15046 step-down controller uses a PWM volt-

age-mode control scheme (see the Functional Diagram).

Control-loop compensation is external for providing max-

imum flexibility in choosing the operating frequency and

output LC filter components. An internal transconduc-

tance error amplifier produces an integrated error volt-

age at COMP that helps to provide higher DC accuracy.

The voltage at COMP sets the duty cycle using a PWM

comparator and a ramp generator. On the rising edge

of an internal clock, the high-side n-channel MOSFET

turns on and remains on until either the appropriate duty

cycle or the maximum duty cycle is reached. During

the on-time of the high-side MOSFET, the inductor cur-

rent ramps up. During the second-half of the switching

cycle, the high-side MOSFET turns off and the low-side

n-channel MOSFET turns on. The inductor releases the

stored energy as the inductor current ramps down, pro-

viding current to the output. Under overload conditions,

when the inductor current exceeds the selected valley

current-limit threshold (see the Current-Limit Circuit (LIM)

section), the high-side MOSFET does not turn on at the

subsequent clock rising edge and the low-side MOSFET

remains on to let the inductor current ramp down.

Internal 5.25V Linear Regulator

An internal linear regulator (VCC) provides a 5.25V nomi-

nal supply to power the internal functions and to drive the

low-side MOSFET. Connect IN and VCC together when

using an external 5V Q10% power supply. The maximum

regulator input voltage (VIN) is 40V. Bypass IN to GND

with a 1FF ceramic capacitor. Bypass the output of the

linear regulator (VCC) with a 4.7FF ceramic capacitor to

GND. The VCC dropout voltage is typically 180mV. When

VIN is higher than 5.5V, VVCC is typically 5.25V. The

MAX15046 also employs an undervoltage lockout circuit

that disables the internal linear regulator when VVCC

falls below 3.6V (typical). The 400mV UVLO hysteresis

prevents chattering on power-up/power-down.

MOSFET Gate Drivers (DH, DL)

DH and DL are optimized for driving large-size n-channel

power MOSFETs. Under normal operating conditions and

after startup, the DL low-side drive waveform is always

the complement of the DH high-side drive waveform,

with controlled dead time to prevent crossconduction or

âshoot-through.â An adaptive dead-time circuit monitors

the DH and DL outputs and prevents the opposite-side

MOSFET from turning on until the MOSFET is fully off.

Thus, the circuit allows the high-side driver to turn on

only when the DL gate driver has turned off preventing

the low side (DL) from turning on until the DH gate driver

has turned off.

The adaptive driver dead time allows operation without

shoot-through with a wide range of MOSFETs, minimiz-

ing delays and maintaining efficiency. There must be a

low-resistance, low-inductance path from DL and DH to

the MOSFET gates for the adaptive dead-time circuits

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