4.5V to 40V Input Automotive

Flyback/Boost/SEPIC Power-Supply Controllers

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Detailed Description

The MAX15004A/B/MAX15005A/B are high-perfor-

mance, current-mode PWM controllers for wide input-

voltage range isolated/nonisolated power supplies.

These controllers are for use as general-purpose boost,

flyback, and SEPIC controllers. The input voltage range

of 4.5V to 40V makes it ideal in automotive applications

such as vacuum fluorescent display (VFD) power sup-

tor) enables the MAX15004A/B/MAX15005A/B to

operate directly from an automotive battery input. The

input operating range can be as low as 2.5V when an

external source (e.g. bootstrap winding output) is

range allows device operation from cold crank to auto-

motive load dump.

The undervoltage lockout (ON/

OFF) allows the devices

to program the input-supply startup voltage and ensures

predictable operation during brownout conditions.

and REG5 regulator output voltage at 5V ±2%. The

sinking up to 30mA current. The input undervoltage

below 3.5V (typ). See the

REG5 section for a method to obtain lower than 4.5V

input operation with the MAX15004/MAX15005.

An external resistor and capacitor network programs

the switching frequency from 15kHz to 500kHz. The

MAX15004A/B/MAX15005A/B provide a SYNC input for

synchronization to an external clock. The OUT (FET-dri-

ver output) duty cycle for the MAX15004A/B is 50%.

The maximum duty cycle can be set on MAX15005A/B

by selecting the right combination of RT and CT. The

RTCT discharge current is trimmed to 2%, allowing

accurate setting of the duty cycle for the MAX15005.

An internal slope-compensation circuit stabilizes the

current loop when operating at higher duty cycles and

can be programmed externally.

The MAX15004/MAX15005 include an internal error

amplifier with 1% accurate reference to regulate the

output in nonisolated topologies using a resistive

divider. The internal reference connected to the nonin-

verting input of the error amplifier can be increased in a

controlled manner to obtain soft-start. A capacitor con-

nected at SS to ground programs soft-start to reduce

inrush current and prevent output overshoot.

The MAX15004/MAX15005 include protection features

like hiccup current limit, output overvoltage, and thermal

shutdown. The hiccup current-limit circuit reduces the

power delivered to the electronics powered by the

MAX15004/MAX15005 converter during severe fault con-

ditions. The overvoltage circuit senses the output using

the path different from the feedback path to provide

meaningful overvoltage protection. During continuous

high input operation, the power dissipation into the

MAX15004/MAX15005 could exceed its limit. Internal

thermal shutdown protection safely turns off the converter

when the junction heats up to 160°C.

Current-Mode Control Loop

The advantages of current-mode control overvoltage-

mode control are twofold. First, there is the feed-for-

ward characteristic brought on by the controller’s ability

to adjust for variations in the input voltage on a cycle-

by-cycle basis. Secondly, the stability requirements of

the current-mode controller are reduced to that of a sin-

gle-pole system unlike the double pole in voltage-mode

control.

The MAX15004/MAX15005 offer peak current-mode

control operation to make the power supply easy to

design with. The inherent feed-forward characteristic is

useful especially in an automotive application where the

input voltage changes fast during cold-crank and load

dump conditions. While the current-mode architecture

offers many advantages, there are some shortcomings.

For higher duty-cycle and continuous conduction mode

operation where the transformer does not discharge

during the off duty cycle, subharmonic oscillations

appear. The MAX15004/MAX15005 offer programmable

slope compensation using a single capacitor. Another

issue is noise due to turn-on of the primary switch that

may cause the premature end of the on cycle. The cur-

rent-limit and PWM comparator inputs have leading-

edge blanking. All the shortcomings of the

current-mode control are addressed in the MAX15004/

MAX15005, making it ideal to design for automotive

power conversion applications.

The internal LDO converts the automotive battery volt-

put is set at 7.4V and operates in a dropout mode at

input voltages below 7.5V. The internal LDO is capable

of delivering 20mA current, enough to provide power to

internal control circuitry and the gate drive. The regulat-

absolute maximum gate voltage rating of the MOSFET

especially during the double battery and load dump

conditions. An auxiliary winding output can be fed to

The bootstrap winding is not necessary for proper