MAX5092EVKIT+ Maxim Integrated Products, MAX5092EVKIT+ Datasheet - Page 18

• Manufacturer Part Number: MAX5092EVKIT+
• Description: KIT EVALUATION FOR MAX5092
• Manufacturer: Maxim Integrated Products

Specifications of MAX5092EVKIT+

• Main Purpose: DC/DC, Step Up with LDO
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 5V
• Current - Output: 250mA
• Voltage - Input: 4 ~ 72V
• Regulator Topology: Buck-Boost
• Board Type: Fully Populated
• Utilized Ic / Part: MAX5092B
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Frequency - Switching: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

The input current waveform of the boost converter is
continuous, and usually does not demand high capaci-
tance at its input. However, the MAX5092_/MAX5093_
boost converter is designed to fully turn on as soon as
the input drops below a certain voltage in order to ride
out cold-crank droops. This operation demands low
input source impedance for proper operation. If the
source (battery) is located far from the IC, high-capaci-
ty, low-ESR capacitors are recommended for C
worst-case peak capacitor current could be as high as
3A. Use a 47µF, 100mΩ low-ESR capacitor placed as
close as possible to the input of the device. Note that
the aluminum electrolytic capacitor ESR increases sig-
nificantly at cold temperatures. In the cold temperature
case, choose an electrolyte capacitor with ESR lower
than 40mΩ or connect a low-ESR ceramic capacitor
(10µF) in parallel with the electrolytic capacitor.
The boost converter output (BSOUT) is fed to the input
of the internal 250mA LDO. The boost-converter output
current waveform is discontinuous and requires high-
capacity, low-ESR capacitors at BSOUT to ensure low
V
the BSOUT capacitor supplies 250mA current to the
LDO input. During the off-time, the inductor dumps cur-
rent into the output capacitor while supplying the output
load current. The internal 250mA LDO is designed with
high PSRR; however, high-frequency spikes may not be
rejected by the LDO. Thus, high-value, low-ESR elec-
trolytic capacitors are recommended for C
Peak-to-peak V
electrolyte capacitor. Use the following equation to cal-
culate the required ESR (ESR
capacitor:
4V to 72V Input LDOs with Boost Preregulator
18
BSOUT
______________________________________________________________________________________
ripple. During the on-time of the internal MOSFET,
Boost Capacitor (C
BSOUT
ESR
BSOUT
ripple depends on the ESR of the
Input Capacitor (C
Design Guidelines
=
I
LIM
Δ
V
BSOUT
ESRBS
−
BSOUT
I
OUT
) of the BSOUT
) Selection
IN
BSOUT
IN
) and
. The
.
where ΔV
BSOUT, I
and I
lower ESR electrolytic capacitor. Make sure the ESR at
cold temperatures does not cause excessive ripple
voltage. Alternately, use a 10µF ceramic capacitor in
parallel with the electrolyte capacitor.
During the switch on-time, the BSOUT capacitor dis-
charges while supplying I
the capacitor discharge (ΔV
the following equation:
where I
the BSOUT capacitance.
The control scheme of the MAX5092/MAX5093 permits
flexibility in choosing an inductor value. Smaller induc-
tance values typically offer smaller physical size for a
given series resistance, allowing the smallest overall
circuit dimensions. Circuits using larger inductance
may provide higher efficiency and exhibit less ripple,
but also may reduce the maximum output current. This
occurs when the inductance is sufficiently large to pre-
vent the LX current limit (I
before the maximum on-time (t
For maximum output current, choose the inductor value
so that the controller reaches the current limit before
the maximum on-time is reached:
where t
(I
Characteristics ). Choose an inductor with the maximum
saturation current (I
LIM
OUT
) is a maximum of 3A (see the Electrical
ON-MAX
OUT
LIM
ESRBS
is the LDO output current. Use a 100mΩ or
is the LDO output current and C
is the internal switch current limit (3A max),
ΔV
CBS
is typically 2.25µs, and the current limit
is 75% of total peak-to-peak ripple at
L
SAT
≤
=
V
I
OUT
) greater than 3A.
IN
×
C
I
t
OUT
LIM
×
ON MAX
BSOUT
CBS
LIM
2 7 10
.
ON-MAX
−
. The ripple caused by
Inductor Selection
) is estimated by using
) from being reached
×
−
6
) expires.
BSOUT
is