MAX20004 datasheet(10/20 Pages) MAXIM

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Detailed Description

The MAX20004/MAX20006/MAX2008 are 4A, 6A, and

8A current-mode step-down converters, respectively,

with integrated high-side and low-side MOSFETs. The

low-side MOSFET enables fixed-frequency FPWM opera-

tion in light-load applications. The devices operate with

3.5V to 36V input voltages, while using only 25μA (typ)

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 devices’

output voltage is available as fixed 5V or 3.3V, or adjust-

able between 1V and 10V. The wide input voltage range,

along with the ability to operate at 99% duty cycle during

undervoltage transients, make these devices ideal for

automotive applications.

In light-load applications, a logic input (SYNC) allows

the devices to operate either in skip mode for reduced

current consumption, or fixed-frequency FPWM mode

to eliminate frequency variation and help minimize EMI.

Protection features include cycle-by-cycle current limit,

and thermal shutdown with automatic recovery.

Thermal Considerations

The devices are available in 4A, 6A, or 8A versions; how-

ever, the average output-current capability is dependent on

several factors. Some of the key factors include the maxi-

mum ambient temperature (TA(MAX)), switching frequency

(fSW), and the number of layers and the size of the PCB.

See the Typical Operating Characteristics for a guideline.

Wide Input Voltage Range

The devices include two separate supply inputs (SUP and

SUPSW) specified for a wide 3.5V to 36V input voltage

range. VSUP provides power to the device and VSUPSW

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 the SUP and SUPSW pins

to drop below the programmed output voltage. Under such

conditions, the devices operate in a high duty-cycle mode

to facilitate minimum dropout from input to output.

Maximum Duty-Cycle Operation

The devices have an effective maximum duty cycle of 98%

(typ). The IC continuously monitors the time between low-

side FET switching cycles in both PWM and skip modes.

Whenever the low-side FET has not switched for more than

13.5µs (typ), the low-side FET is forced on for 150ns (typ)

to refresh the BST capacitor. The input voltage at which

the device enters dropout changes depending on the input

voltage, output voltage, switching frequency, load current,

and the efficiency of the design.

The input voltage at which the device enters dropout can

be approximated as:

OUT

SUP

OUT

0.98

+×

where RHS is the high-side switch on-resistance, which

should also include the inductor DC resistance for better

accuracy.

Linear Regulator Output (BIAS)

The devices include a 5V linear regulator (VBIAS) that

provides power to the internal circuit blocks. Connect

a 2.2μF ceramic capacitor from BIAS to GND. Under

certain conditions, the BIAS regulator turns off and the

BIAS pin switches to OUT (i.e., switches over) after

startup to increase efficiency. For IC versions that are

factory trimmed for 3.3V fixed output, BIAS switches to

OUT under light load conditions in skip mode only. For IC

versions that are factory trimmed for 5V fixed output, the

BIAS pin switches to OUT after startup regardless of load

or skip/PWM mode. In any case, BIAS only switches over

if OUT is between 2.8V and 5.6V. In summary, BIAS can

transition from 5V to VOUT after startup depending on

load, mode and IC version.

Soft-Start

The devices include a fixed, internal soft-start. Soft-start

limits startup inrush current by forcing the output voltage

to ramp up towards its regulation point.

Reset Output (RESET)

The devices feature an open-drain reset output (RESET).

RESET

asserts when VOUT drops below the specified

falling threshold. RESET deasserts when VOUT rises

above the specified rising threshold after the specified

hold time. Connect RESET to the output or I/O voltage

of choice (within pin voltage limits) with a pullup resistor.

Synchronization Input (SYNC)

SYNC is a logic-level input used for operating-mode

selection and frequency control. Connecting SYNC to

BIAS or to an external clock enables forced fixed-frequen-

cy (FPWM) operation. Connecting SYNC to GND enables

automatic skip-mode operation for light load efficiency.

The external clock frequency at SYNC can be higher or

lower than the internal clock by 20%. If the external clock

frequency is greater than 120% of the internal clock, con-

tact the factory to verify the design. The devices synchro-

nize to the external clock in two cycles. When the external

clock signal at SYNC is absent for more than two clock

cycles, the devices use the internal clock. There is a diode

MAX20004/MAX20006/

MAX20008

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

Fully Integrated Automotive

Step-Down Converters

www.maximintegrated.com

Maxim Integrated │ 10

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