Datasheet
4.5V to 40V Input Automotive
Flyback/Boost/SEPIC Power-Supply Controllers
n-Channel MOSFET Driver
OUT drives the gate of an external n-channel MOSFET.
The driver is powered by the internal regulator (V
CC
),
internally set to approximately 7.4V. If an external voltage
higher than 7.4V is applied at V
CC
(up to 10V), it appears
as the peak gate drive voltage. The regulated V
CC
volt-
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.
Error Amplifier
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
REF
= 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 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
SLOPE
is the external capacitor at SLOPE in
farads.
Current Limit
The current-sense resistor (R
CS
), connected between
the source of the MOSFET and ground, sets the current
limit. The CS input has a voltage trip level (V
CS
) 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 R
S
:
where I
PRI
is the peak current that flows through the
MOSFET at full load and minimum V
IN
.
R
V
I
S
CS
PRI
=
Slope compensation mV s
A
C
SLOPE
()
.()
μ=
×
−
25 10
9
V
R
R
V
OUT
A
B
REF
=+
⎛
⎝
⎜
⎞
⎠
⎟
1
Figure 3a. MAX15005 Maximum Duty Cycle vs. Output
Frequency.
MAX15005 MAXIMUM DUTY CYCLE
vs. OUTPUT FREQUENCY (f
OUT
)
OUTPUT FREQUENCY (kHz)
MAXIMUM DUTY CYCLE (%)
50
55
60
65
70
75
80
85
90
95
100
10 100 1000
CT = 220pF
CT = 1500pF
CT = 1000pF
CT = 560pF
CT = 2200pF
CT = 3300pF
CT = 100pF
Figure 3b. Oscillator Frequency vs. RT/CT
OSCILLATOR FREQUENCY (f
OSC
)
vs. RT/CT
RT (kΩ)
OSCILLATOR FREQUENCY (kHz)
1 10 100 1000
10
100
1000
CT = 220pF
CT = 1500pF
CT = 1000pF
CT = 560pF
CT = 2200pF
CT = 3300pF
CT = 100pF
MAX15004A/B/MAX15005A/B
14
Maxim Integrated