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between SYNC and BIAS, so it is important when driving

SYNC with an external source that the voltage be less

than or equal to BIAS (or OUT in the case of switchover).

If this cannot be guaranteed, place a series resistor in-line

with SYNC ≥ 20kΩ to limit the input current. If EN is low,

BIAS is turned off so a voltage should not be present on

SYNC without the series resistor.

System Enable (EN)

An enable control input (EN) activates the devices from

their low-power shutdown mode. EN is compatible with

inputs from automotive battery level down to 3.5V.

EN turns on the internal linear (BIAS) regulator. Once

VBIAS is above the internal lockout threshold (VUVBIAS =

3V (typ)), the converter activates and the output voltage

ramps up with the programmed soft-start time.

A logic-low at EN shuts down the device. During shut-

down, the BIAS regulator and gate drivers turn off.

Shutdown is the lowest power state and reduces the

quiescent current to 5μA (typ). Drive EN high to bring the

device out of shutdown.

For safe startup, ensure that VSUP > 7.5V when EN is

toggled high. In all applications, BIAS capacitance guide-

lines must be followed to ensure safe operation of the IC.

Note: In all applications, BIAS must start from < 0.3V or

> 1.6V during startup.

Spread-Spectrum Option

The devices can be ordered with spread spectrum

enabled. See the Ordering Information/Selector Guide

section. When the spread spectrum is factory enabled,

the operating frequency is varied ±3% centered on FOSC.

The modulation signal is a triangular wave with a fre-

quency of 4.5kHz at 2.2MHz.

For operations at FOSC values other than 2.2MHz, the

modulation signal scales proportionally (e.g., at 400kHz,

the modulation frequency reduces by 0.4MHz/2.2MHz).

The internal spread spectrum is disabled if the devices

are synchronized to an external clock. However, the

devices do not filter the input clock on the SYNC pin and

pass any modulation (including spread spectrum) present

driving the external clock.

Internal Oscillator (FOSC)

The switching frequency (fSW) is set by a resistor

(RFOSC) connected from FOSC to GND. To determine

the approximate value of RFOSC for a given fSW, use the

graph in the Typical Operating Characteristics section or

the following equation:

FOSC

29,600

1.48

−

where fSW is in kHz and RFOSC is in kΩ. For example, a

400kHz switching frequency is set with RFOSC = 72.5kΩ.

Higher frequencies allow designs with lower inductor

values and less output capacitance at the expense of

reduced efficiency and higher EMI.

Thermal-Shutdown Protection

Thermal shutdown protects the device from excessive

operating temperature. When the junction temperature

exceeds the specified threshold, an internal sensor shuts

down the internal bias regulator and the step-down con-

verter, allowing the IC to cool. The sensor turns the IC on

again after the junction temperature cools by the specified

hysteresis.

Current Limit/Short-Circuit Protection

The devices feature a current limit that protects them

against short-circuit and overload conditions at the out-

put. In the event of a short-circuit or overload condition,

the high-side MOSFET remains on until the inductor

current reaches the specified LX current-limit threshold.

The converter then turns the high-side MOSFET off and

the low-side MOSFET on to allow the inductor current to

ramp down. Once the inductor current crosses below the

current-limit threshold, the converter turns on the high-

side MOSFET again. This cycle repeats until the short or

overload condition is removed.

A hard short is detected when the output voltage falls

below 50% of the target while in current limit. If this

occurs, hiccup mode activates, and the output turns off

for four times the soft-start time. The output then enters

soft-start and powers back up. This repeats indefinitely

while the short circuit is present. Hiccup mode is disabled

during soft-start.

Overvoltage Protection

If the output voltage exceeds the OV protection rising

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

side MOSFET turns on. Normal operation resumes when

the output voltage goes below the falling OV threshold.

MAX20004/MAX20006/

MAX20008

36V, 220kHz to 2.2MHz, 4A/6A/8A

Fully Integrated Automotive

Step-Down Converters

www.maximintegrated.com

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