MAX15005 Maxim Integrated Products, MAX15005 Datasheet - Page 14

• Manufacturer Part Number: MAX15005
• Description: (MAX15004 / MAX15005) 4.5V to 40V Input Automotive Flyback/Boost/SEPIC Power-Supply Controllers
• Manufacturer: Maxim Integrated Products

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OUT drives the gate of an external n-channel MOSFET.
The driver is powered by the internal regulator (V
internally set to approximately 7.4V. If an external voltage
higher than 7.4V is applied at V
as the peak gate drive voltage. The regulated V
age keeps the OUT voltage below the maximum gate
voltage rating of the external MOSFET. OUT can source
750mA and sink 1000mA peak current. The average cur-
rent sourced by OUT depends on the switching frequen-
cy and total gate charge of the external MOSFET.
The MAX15004A/B/MAX15005A/B include an internal
error amplifier. The noninverting input of the error
amplifier is connected to the internal 1.228V reference
and feedback is provided at the inverting input. High
100dB open-loop gain and 1.6MHz unity-gain band-
width allow good closed-loop bandwidth and transient
response. Moreover, the source and sink current capa-
bility of 2mA provides fast error correction during the
output load transient. For Figure 5, calculate the power-
supply output voltage using the following equation:
where V
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.
4.5V to 40V Input Automotive
Flyback/Boost/SEPIC Power-Supply Controllers
Figure 3a. MAX15005 Maximum Duty Cycle vs. Output
Frequency.
14
______________________________________________________________________________________
REF
= 1.228V. The amplifier’s noninverting input
100
95
90
85
80
75
70
65
60
55
50
10
CT = 3300pF
V
CT = 2200pF
CT = 1500pF
MAX15005 MAXIMUM DUTY CYCLE
OUT
CT = 1000pF
vs. OUTPUT FREQUENCY (f
n-Channel MOSFET Driver
OUTPUT FREQUENCY (kHz)
=
⎛
⎜
⎝
1
CT = 560pF
+
R
R
100
CC
B
A
⎞
⎟
⎠
CT = 220pF
(up to 10V), it appears
V
REF
Error Amplifier
CT = 100pF
OUT
)
1000
CC
CC
volt-
),
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 con-
nected 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:
where C
farads.
The current-sense resistor (R
the source of the MOSFET and ground, sets the current
limit. The CS input has a voltage trip level (V
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 R
where I
MOSFET at full load and minimum V
Figure 3b. Oscillator Frequency vs. RT/CT
Slope compensation mV s
PRI
SLOPE
1000
is the peak current that flows through the
100
10
S
:
1
is the external capacitor at SLOPE in
CT = 1500pF
CT = 2200pF
CT = 3300pF
OSCILLATOR FREQUENCY (f
R
S
10
=
(
vs. RT/CT
RT (kΩ)
V
I
Slope Compensation
PRI
CS
CS
μ
), connected between
)
100
=
CT = 100pF
IN
CT = 220pF
CT = 560pF
CT = 1000pF
2 5 10
.
.
Current Limit
OSC
C
×
SLOPE
)
1000
−
9
( )
A
CS
) of
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