MAX5083ATE datasheet(10/18 Pages) MAXIM

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omitted and the input voltage range is from 7.5V to 40V.

In this situation, the boost diode and the boost capacitor

are still required (see the MAX5083 Typical Operating

Circuit).

Gate Drive Supply (DVREG)

DVREG is the supply input for the internal high-side

MOSFET driver. The power for DVREG is derived from

the output of the internal regulator (REG). Connect

DVREG to REG externally. We recommend the use of an

RC (1Ω and 0.47μF) filter from REG to DVREG to filter

the noise generated by the switching of the charge pump.

In the MAX5082, the high-side drive supply is generated

using the internal charge pump along with the bootstrap

diode and capacitor. In the MAX5083, the high-side

MOSFET driver supply is generated using only the boot-

strap diode and capacitor.

Error Amplifier

The output of the internal error amplifier (COMP) is avail-

able for frequency compensation (see the Compensation

Design section). The inverting input is FB, the noninvert-

ing input SS, and the output COMP. The error amplifier

has an 80dB open-loop gain and a 1.8MHz GBW product.

See the Typical Operating Character-istics for the Gain

and Phase vs. Frequency graph.

Oscillator/Synchronization Input (SYNC)

With SYNC tied to SGND, the MAX5082/MAX5083 use

their internal oscillator and switch at a fixed frequency of

250kHz. For external synchronization, drive SYNC with

an external clock from 150kHz to 350kHz. When driven

with an external clock, the device synchronizes to the ris-

ing edge of SYNC.

PWM Comparator/Voltage Feed-Forward

An internal 250kHz ramp generator is compared against

the output of the error amplifier to generate the PWM

signal. The maximum amplitude of the ramp (VRAMP)

automatically adjusts to compensate for input voltage and

oscillator frequency changes. This causes the VIN/VRAMP

to be a constant 10V/V across the input voltage range of

4.5V to 40V (MAX5082) or 7.5V to 40V (MAX5083) and

the SYNC frequency range of 150kHz to 350kHz.

Output Short-Circuit Protection

(Hiccup Mode)

The MAX5082/MAX5083 protects against an output short

circuit by utilizing hiccup-mode protection. In hiccup mode,

a series of sequential cycle-by-cycle current-limit events

will cause the part to shut down and restart with a soft-start

sequence. This allows the device to operate with a continu-

ous output short circuit.

During normal operation, the current is monitored at the

drain of the internal power MOSFET. When the current

limit is exceeded, the internal power MOSFET turns off until

the next on-cycle and a counter increments. If the counter

counts four consecutive current-limit events, the device

discharges the soft-start capacitor and shuts down for 512

clock periods before restarting with a soft-start sequence.

Each time the power MOSFET turns on and the device

does not exceed the current limit, the counter is reset.

Thermal-Overload Protection

The MAX5082/MAX5083 feature an integrated ther-

maloverload protection. Thermal-overload protection lim-

its the total power dissipation in the device and protects

it in the event of an extended thermal fault condition.

When the die temperature exceeds +160°C, an internal

thermal sensor shuts down the part, turning off the power

MOSFET and allowing the IC to cool. After the tempera-

ture falls by 20°C, the part will restart with a soft-start

sequence.

Applications Information

Setting the Undervoltage Lockout

When the voltage at ON/OFF rises above 1.23V, the

MAX5082/MAX5083 turns on. Connect a resistive divider

from IN to ON/OFF to SGND to set the UVLO threshold

(see Figure 5). First select the ON/OFF to the SGND resis-

tor (R2) then calculate the resistor from IN to ON/OFF (R1)

using the following equation:

ON/OFF

R1 R2

−





× 











where VIN is the input voltage at which the converter

turns on, VON/OFF = 1.23V and R2 is chosen to be less

than 600kΩ.

If the external UVLO divider is not used, connect ON/OFF

to IN directly. In this case, an internal undervoltage lock-

out feature monitors the supply voltage at IN and allows

operation to start when IN rises above 4.1V (MAX5082)

and 7.1V (MAX5083).

Setting the Output Voltage

Connect a resistive divider from OUT to FB to SGND

to set the output voltage (see Figure 5). First calculate

the resistor from OUT to FB using the guidelines in the

Compensation Design section. Once R3 is known, calcu-

late R4 using the following equation:

MAX5082/MAX5083

1.5A, 40V, MAXPower Step-Down

DC-DC Converters

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