Spread-Spectrum Option
The spread spectrum can be enabled on the device
using a pin. When the SPS pin is pulled high the spread
spectrum is enabled and the operating frequency is varied
±3% centered on FOSC. The modulation signal is a trian-
gular wave with a period of 110μs at 2.2MHz. Therefore,
FOSC ramps down 3% and back to 2.2MHz in 110μs and
also ramps up 3% and back to 2.2MHz in 110μs. The
cycle repeats.
For operations at FOSC values other than 2.2MHz, the
modulation signal scales proportionally (e.g., at 400kHz,
the 110μs modulation period increases to 110μs x
2.2MHz/0.4MHz = 550μs).
The internal spread spectrum is disabled if the devices
are synchronized to an external clock. However, the
devices do not filter the input clock on the FSYNC pin and
pass any modulation (including spread spectrum) present
on the driving external clock.
Internal Oscillator (FOSC)
The switching frequency (f
SW
) is set by a resistor (R
FOSC
)
connected from FOSC to AGND. For example, a 400kHz
switching frequency is set with R
FOSC
= 73.2kΩ. Higher
frequencies allow designs with lower inductor values and
less output capacitance. Consequently, peak currents and
I
2
R losses are lower at higher switching frequencies, but
core losses, gate-charge currents, and switching losses
increase.
Overtemperature Protection
Thermal overload protection limits the total power
dissipation in the device. When the junction temperature
exceeds 175°C (typ), an internal thermal sensor shuts
down the internal bias regulator and the step-down
converter, allowing the IC to cool. The thermal sensor
turns on the IC again after the junction temperature cools
by 15°C.
Overvoltage Protection (OVP)
If the output voltage reaches the OVP threshold, the
high-side switch is forced off and the low-side switch
is forced on until the negative-current limit is reached.
After negative-current limit is reached, both the high-side
and low-side switches are turned off. The MAX20002C
and MAX20003C feature an additional clamp and lower
OVP threshold to limit the output-voltage overshoot for
automotive conditions. Contact the Maxim Applications
team to determine if the MAX20002C/MAX20003C are
needed for your application.
Applications Information
Setting the Output Voltage
Connect FB to BIAS for a fixed +5V/3.3V output voltage.
To set the output to other voltages between 1V and 10V,
connect a resistive divider from output (OUT) to FB to
AGND (Figure 2). Select R
FB2
(FB to AGND resistor)
less than or equal to 500kΩ. Calculate R
FB1
(OUT to FB
resistor) with the following equation:
OUT
FB1 FB2
FB
V
R R -1
V
=
where VFB = 1V (see the
Electrical Characteristics
table).
Forced-PWM and Skip Modes
In PWM mode of operation, the devices switch at
a constant frequency with variable on-time. In skip
mode of operation, the converter’s switching frequency
is load dependent. At higher load current, the switching
frequency does not change and the operating mode is
similar to the PWM mode. Skip mode helps improve
efficiency in light-load applications by allowing the
converters to turn on the high-side switch only when the
output voltage falls below a set threshold. As such, the
converters do not switch MOSFETs on and off as often
as in the PWM mode. Consequently, the gate charge and
switching losses are much lower in skip mode.
Figure 2. Adjustable Output-Voltage Setting
R
FB1
R
FB2
V
OUT
MAX20002
MAX
20003
FB
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Maxim Integrated
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13
MAX20002/MAX20003 36V, 220kHz to 2.2MHz, 2A/3A Fully
Integrated Step-Down Converters
with 15μA Operating Current