MAX1980ETP+ Maxim Integrated Products, MAX1980ETP+ Datasheet - Page 23

• Manufacturer Part Number: MAX1980ETP+
• Description: IC CNTRLR QUICK-PWM 20-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX1980ETP+

• Pwm Type: Controller
• Number Of Outputs: 1
• Frequency - Max: 550kHz
• Duty Cycle: 50%
• Voltage - Supply: 4 V ~ 28 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: 0°C ~ 85°C
• Package / Case: 20-TQFN Exposed Pad
• Frequency-max: 550kHz
• Input Voltage: 4 V to 28 V
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 100 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

For in-phase operation, the maximum ESR to meet rip-
ple requirements is:
The actual capacitance value required relates to the
physical size needed to achieve low ESR, as well as to
the chemistry of the capacitor technology. Thus, the
capacitor is usually selected by ESR and voltage rating
rather than by capacitance value (this is true of tanta-
lums, OS-CONs, and other electrolytics).
When using low-capacity filter capacitors such as
ceramic or polymer types, capacitor size is usually
determined by the capacity needed to prevent V
and V
sients. Generally, once enough capacitance is added to
meet the overshoot requirement, undershoot at the ris-
ing load edge is no longer a problem (see the V
V
For Quick-PWM controllers, stability is determined by
the value of the ESR zero relative to the switching fre-
quency. The boundary of instability is given by the fol-
lowing equation:
For a standard 300kHz application, the ESR zero fre-
quency must be well below 95kHz, preferably below
50kHz. Tantalum, Sanyo POSCAP, and Panasonic SP
capacitors in wide-spread use at the time of publication
have typical ESR zero frequencies below 30kHz. In the
standard application used for inductor selection, the
ESR needed to support a 30mV
x 0.3) = 2.5mΩ. Eight 270µF/2.0V Panasonic SP capac-
itors in parallel provide 1.9mΩ (max) ESR. Their typical
combined ESR results in a zero at 39kHz.
Do not put high-value ceramic capacitors directly
across the output without taking precautions to ensure
stability. Ceramic capacitors have a high ESR zero fre-
quency and may cause erratic, unstable operation.
However, it’s easy to add enough series resistance by
placing the capacitors a couple of centimeters down-
stream from the junction of the inductor and FB pin.
SOAR
Output Capacitor Stability Considerations
R
ESR
Driver Disable for Multiphase DC-DC Converter
SOAR
equations in the Transient Response section).
≤
I
LOAD MAX
V
from causing problems during load tran-
RIPPLE
where f
(
______________________________________________________________________________________
)
LIR
ESR
f
ESR
=
=



≤
f
2
SW
π
η
f
SW
R
π
L
ESR OUT
P-P






1
V
C
V
ripple is 30mV/(40A
OUT
V
Quick-PWM Slave Controller with
RIPPLE
IN



(
V
IN
−
V
SAG
OUT
SAG
and
)
Unstable operation manifests itself in two related but
distinctly different ways: double-pulsing and feedback
loop instability. Double-pulsing occurs due to noise on
the output or because the ESR is so low that there isn’t
enough voltage ramp in the output voltage signal. This
“fools” the error comparator into triggering a new cycle
immediately after the minimum off-time period has
expired. Double-pulsing is more annoying than harmful,
resulting in nothing worse than increased output ripple.
However, it can indicate the possible presence of loop
instability due to insufficient ESR. Loop instability can
result in oscillations at the output after line or load
steps. Such perturbations are usually damped, but can
cause the output voltage to rise above or fall below the
tolerance limits.
The easiest method for checking stability is to apply a
very fast zero-to-max load transient and carefully
observe the output voltage ripple envelope for over-
shoot and ringing. It can help to simultaneously monitor
the switching waveforms (V
allow more than one cycle of ringing after the initial
step-response under/overshoot.
The input capacitor must meet the ripple current require-
ment (I
MAX1980 multiphase slave controllers operate out-of-
phase (POL = V
of each phase. This minimizes the input ripple current by
dividing the load current among independent phases:
for out-of-phase operation.
When operating the MAX1980 in-phase (POL = GND),
the high-side MOSFETs turn on simultaneously, so
input capacitors must support the combined input rip-
ple currents of each phase:
for in-phase operation.
For most applications, nontantalum chemistries (ceramic,
aluminum, or OS-CON) are preferred because of their
resilience to inrush surge currents typical of systems with
a mechanical switch or connector in series with the input.
RMS
I
RMS
I
RMS
) imposed by the switching currents. The
=
=



CC
I
LOAD
I
LOAD
or float), staggering the turn-on times
η




Input Capacitor Selection







V
OUT IN
V
LX
OUT IN
and/or I
(
V
V
(
IN
V
V
IN
−
V
−
OUT
V
INDUCTOR
OUT
)




)




). Don’t
23