MAX15004AAUE データシートの表示（PDF） - Maxim Integrated

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MAX15004AAUE

4.5V to 40V Input Automotive Flyback/Boost/SEPIC Power-Supply Controllers

Maxim Integrated 

MAX15004A/B-MAX15005A/B

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 supplies. The

internal low-dropout regulator (VCC regulator) enables the

MAX15004A/B/MAX15005A/B to operate directly from an

automotive battery input. The input voltage can go lower

than 4.5V after startup if IN is bootstrapped to a boosted

output voltage.

The undervoltage lockout (ON/OFF) allows the devices

to program the input-supply startup voltage and ensures

predictable operation during brownout conditions.

The devices contain two internal regulators, VCC and

REG5. The VCC regulator output voltage is set at 7.4V

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

undervoltage lockout (UVLO) circuit monitors the VCC

voltage and turns off the converter when the VCC voltage

drops below 3.5V (typ).

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-driver

output) duty cycle for the MAX15004A/B is 50%. The maxi-

mum 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-compen-

sation 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 noninverting input

of the error amplifier can be increased in a controlled

manner to obtain soft-start. A capacitor connected 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 shut-

down. The hiccup current-limit circuit reduces the power

delivered to the electronics powered by the MAX15004/

MAX15005 converter during severe fault conditions. The

overvoltage circuit senses the output using the path differ-

ent from the feedback path to provide meaningful overvolt-

age protection. During continuous high input operation, the

4.5V to 40V Input Automotive

Flyback/Boost/SEPIC

Power-Supply Controllers

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-forward

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 single-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 con-

ditions. 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 current-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.

Internal Regulators VCC and REG5

The internal LDO converts the automotive battery voltage

input to a 7.4V output voltage (VCC). The VCC output is

set at 7.4V and operates in a dropout mode at input volt-

ages 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 regulated VCC keeps the

driver output voltage well below the absolute maximum

gate voltage rating of the MOSFET especially during the

double battery and load dump conditions.

The second 5V LDO regulator from VCC to REG5 provides

power to the internal control circuits. This LDO can also be

used to source 15mA of external load current.

Bypass VCC and REG5 with a parallel combination of 1µF

and 0.1µF low-ESR ceramic capacitors. Additional capaci-

tors (up to 22µF) at VCC can be used although they are

not necessary for proper operation of the MAX15004/

MAX15005.

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