Detailed Description

TheMAX17536high-efficiency,high-voltage,synchronously

rectified step-down converter with integrated high-side

MOSFET operates over a 4.5V to 60V input. It delivers

compensation across the output voltage range eliminates

the need for external components. The feedback (FB)

regulation accuracy over -40°C to +125°C is ±1.4%.

The device features a peak-current-mode control

architecture. An internal transconductance error amplifier

produces an integrated error voltage at an internal node

that sets the duty cycle using a PWM comparator, a high-

side current-sense amplifier, and a slope-compensation

generator. At each rising edge of the clock, the high-

side MOSFET turns on and remains on until either

the appropriate or maximum duty cycle is reached, or

the peak current limit is detected. During the high-side

MOSFET’son-time,theinductorcurrentrampsup.During

the second-half of the switching cycle, the high-side

MOSFET turns off and the low-side MOSFET turns on.

The inductor releases the stored energy as its current

ramps down and provides current to the output.

The device features a MODE/SYNC pin that can be used

to operate the device in PWM, PFM, or DCM control

schemesandtosynchronizetheswitchingfreqeuncyto

an external clock. The device also features adjustable-

input undervoltage lockout, adjustable soft-start, open-

drain RESET, auxiliary bootstrap LDO, and DL-to-LX

short-detection features.

Mode Selection (MODE)

The logic state of the MODE/SYNC pin is latched when

rising thresholds and all internal voltages are ready to

allow LX switching. If the MODE/SYNC pin is open at

power-up, the device operates in PFM mode at light

loads. If the MODE/SYNC pin is grounded at power-up,

the device operates in constant-frequency PWM mode

at all loads. Finally, if the MODE/SYNC pin is connected

frequency DCM mode at light loads. State changes on the

MODE/SYNC pin are ignored during normal operation.

PWM Mode Operation

In PWM mode, the inductor current is allowed to go nega-

tive. PWM operation provides constant frequency opera-

tion at all loads, and is useful in applications sensitive to

switchingfrequency.However,thePWMmodeofopera-

tion gives lower efficiency at light loads compared to PFM

and DCM modes of operation.

PFM Mode Operation

PFM mode of operation disables negative inductor current

and additionally skips pulses at light loads for high

efficiency. In PFM mode, the inductor current is forced

to a fixed peak of 2A every clock cycle until the output

rises to 102.3% of the nominal voltage. Once the output

reaches 102.3% of the nominal voltage, both the high-side

and low-side FETs are turned off and the device enters

hibernate operation until the load discharges the output to

101.1% of the nominal voltage. Most of the internal blocks

are turned off in hibernate operation to save quiescent

current. After the output falls below 101.1% of the nominal

voltage, the device comes out of hibernate operation,

turns on all internal blocks, and again commences the

process of delivering pulses of energy to the output until it

reaches 102.3% of the nominal output voltage.

The advantage of the PFM mode is higher efficiency at

light loads because of lower quiescent current drawn from

the supply. The disadvantage is that the output-voltage

ripple is higher compared to PWM or DCM modes of

operation and switching frequency is not constant at light

loads.

DCM Mode Operation

DCM mode of operation features constant-frequency

operation down to lighter loads than PFM mode, by not

skipping pulses but only disabling negative inductor

current at light loads. DCM operation offers efficiency

performance that lies between PWM and PFM modes.

ThedevicehastwointernalLDO(low-dropout)regulators

LDO) and the other LDO is powered from EXTVCC

(EXTVCCLDO).OnlyoneofthetwoLDOsisinoperation

at a time, depending on the voltage levels present at

EXTVCC. If EXTVCC voltage is greater than 4.7V (typ),

EXTVCC increases efficiency at higher input voltages.

EXTVCC voltage should not exceed 24V.

the internal blocks and the low-side MOSFET driver and

re-chargestheexternalbootstrapcapacitor.BothINLDO

and EXTVCC LDO can source up to 45mA for bias

requirements. The MAX17536 employs an undervoltage-

falls below 3.8V (typ). The converter is enabled again

chattering on power-up/power-down.

Maxim Integrated │ 12

MAX17536

4.5V to 60V, 4A, High-Efficiency, Synchronous

Step-Down DC-DC Converter

with Internal Compensation

www.maximintegrated.com