MAX15004A 데이터 시트보기 (PDF) - Maxim Integrated
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MAX15004A Datasheet PDF : 27 Pages
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MAX15004A/B-MAX15005A/B
4.5V to 40V Input Automotive
Flyback/Boost/SEPIC
Power-Supply Controllers
MAX15005 MAXIMUM DUTY CYCLE
vs. OUTPUT FREQUENCY (fOUT)
100
95
CT = 100pF
90
85
80
75 CT = 3300pF
70 CT = 2200pF
65 CT = 1500pF
60
55
CT = 1000pF CT = 560pF
CT = 220pF
50
10
100
1000
OUTPUT FREQUENCY (kHz)
Figure 3a. MAX15005 Maximum Duty Cycle vs. Output
Frequency.
Moreover, the source and sink current capability of 2mA
provides fast error correction during the output load
transient. For Figure 5, calculate the power-supply output
voltage using the following equation:
VOUT=
1 +
R
R
A
B
VREF
where VREF = 1.228V. The amplifier’s noninverting input
is internally connected to a soft-start circuit that gradu-
ally increases the reference voltage during startup. This
forces the output voltage to come up in an orderly and
well-defined manner under all load conditions.
Slope Compensation
The MAX15004A/B/MAX15005A/B use an internal ramp
generator for slope compensation. The internal ramp
signal resets at the beginning of each cycle and slews at
the rate programmed by the external capacitor connected
to SLOPE. The amount of slope compensation needed
depends on the downslope of the current waveform.
Adjust the MAX15004A/B/MAX15005A/B slew rate up to
110mV/μs using the following equation:
Slope compensation (mV µs) = 2.5 × 10 −9(A)
C SLOPE
where CSLOPE is the external capacitor at SLOPE in
farads.
OSCILLATOR FREQUENCY (fOSC)
vs. RT/CT
1000
CT = 100pF
CT = 220pF
CT = 560pF
100
CT = 1500pF
CT = 2200pF
CT = 1000pF
CT = 3300pF
10
1
10
100
1000
RT (kΩ)
Figure 3b. Oscillator Frequency vs. RT/CT
Current Limit
The current-sense resistor (RCS), connected between the
source of the MOSFET and ground, sets the current limit.
The CS input has a voltage trip level (VCS) of 305mV. The
current-sense threshold has 5% accuracy. Set the current-
limit threshold 20% higher than the peak switch current at
the rated output power and minimum input voltage. Use
the following equation to calculate the value of RS:
= R S VCS (IPK ×1.2)
where IPRI is the peak current that flows through the
MOSFET at full load and minimum VIN.
When the voltage produced by this current (through the
current-sense resistor) exceeds the current-limit com-
parator threshold, the MOSFET driver (OUT) quickly
terminates the on-cycle. In most cases, a short-time
constant RC filter is required to filter out the leading-edge
spike on the sense waveform. The amplitude and width
of the leading edge depends on the gate capacitance,
drain capacitance (including interwinding capacitance),
and switching speed (MOSFET turn-on time). Set the RC
time constant just long enough to suppress the leading
edge. For a given design, measure the leading spike at
the highest input and rated output load to determine the
value of the RC filter.
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