MAX15004A 데이터 시트보기 (PDF) - Maxim Integrated

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MAX15004A

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

Maxim Integrated 

MAX15004A/B-MAX15005A/B

VIN

REG5

MAX15004A/B

MAX15005A/B

R1

N

RCS

0.3V

CURRENT-LIMIT

COMPARATOR

CCS

RS

Figure 4. Reducing Current-Sense Threshold

The low 305mV current-limit threshold reduces the power

dissipation in the current-sense resistor. The current-limit

threshold can be further reduced by adding a DC offset

to the CS input from REG5 voltage. Do not reduce the

current-limit threshold below 150mV as it may cause

noise issues. See Figure 4. For a new value of the

current-limit threshold (VILIM_LOW), calculate the value of

R1 using the following equation:

R1 = 4.75 × R CS

0.290 − VILIM_LOW

Applications Information

Boost Converter

The MAX15004A/B/MAX15005A/B can be configured for

step-up conversion. The boost converter output can be

fed back to IN through a Schottky diode (see Figure 5) so

the controller can function during low voltage conditions

such as cold-crank. Use a Schottky diode (DVIN) in the

VIN path to avoid backfeeding the input source. Use the

equations in the following sections to calculate inductor

(LMIN), input capacitor (CIN), and output capacitor (COUT)

when using the converter in boost operation.

4.5V to 40V Input Automotive

Flyback/Boost/SEPIC

Power-Supply Controllers

Inductor Selection in Boost Configuration

Using the following equation, calculate the minimum

inductor value so that the converter remains in continuous

mode operation at minimum output current (IOMIN):

where:

and

L MIN

=

2×

VIN2 × D ×

fOUT × VOUT

η

× IOMIN

D = VOUT + VD − VIN

VOUT + VD − VDS

IOMIN = (0.1× IO ) to (0.25 × IO )

The higher value of IOMIN reduces the required

inductance; however, it increases the peak and RMS

currents in the switching MOSFET and inductor. Use

IOMIN from 10% to 25% of the full load current. The VD is

the forward voltage drop of the external Schottky diode,

D is the duty cycle, and VDS is the voltage drop across

the external switch. Select the inductor with low DC

resistance and with a saturation current (ISAT) rating

higher than the peak switch current limit of the converter.

Input Capacitor Selection in Boost

Configuration

The input current for the boost converter is continuous

and the RMS ripple current at the input capacitor is

low. Calculate the minimum input capacitor value and

maximum ESR using the following equations:

where :

CIN

=

4

×

∆IL × D

fOUT × ∆VQ

ESR = ∆VESR

∆IL

∆IL

=(VIN − VDS ) × D

L × fOUT

VDS is the total voltage drop across the external MOSFET

plus the voltage drop across the inductor ESR. ΔIL is

peak-to-peak inductor ripple current as calculated above.

ΔVQ is the portion of input ripple due to the capacitor

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