MAX1980ETP+ Maxim Integrated Products, MAX1980ETP+ Datasheet - Page 18

• 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

During startup, the V
circuitry forces the DL and the DH gate drivers low,
inhibiting switching until an adequate supply voltage is
reached. Once V
detected at the trigger input initiate a corresponding
on-time pulse (see the On-Time Control and Active
Current Balancing section). To ensure correct startup,
the MAX1980 slave controller’s undervoltage lockout
voltage must be lower than the master controller’s
undervoltage lockout voltage.
If the V
there is not enough supply voltage to make valid deci-
sions. To protect the output from overvoltage faults, DL
and DH are forced low, effectively disabling the
MAX1980.
The MAX1980 features a thermal-fault-protection circuit.
When the junction temperature rises above +160°C, a
thermal sensor activates the standby logic, which pulls
DL and DH low. The thermal sensor reactivates the
slave controller after the junction temperature cools by
15°C.
Firmly establish the input voltage range and maximum
load current before choosing a switching frequency
and inductor operating point (ripple-current ratio). The
primary design trade-off lies in choosing a good switch-
ing frequency and inductor operating point, and the fol-
lowing four factors dictate the rest of the design:
Input Voltage Range: The maximum value (V
must accommodate the worst-case high AC adapter
voltage. The minimum value (V
the lowest input voltage after drops due to connectors,
fuses, and battery selector switches. If there is a choice
at all, lower input voltages result in better efficiency.
Maximum Load Current: There are two values to con-
sider. The peak load current (I
the instantaneous component stresses and filtering
requirements, and thus drives output capacitor selec-
tion, inductor saturation rating, and the design of the
current-limit circuit. The continuous load current (I
determines the thermal stresses and thus drives the
selection of input capacitors, MOSFETs, and other criti-
cal heat-contributing components. Modern notebook
CPUs generally exhibit I
For multiphase systems, each phase supports a frac-
tion of the load, depending on the current balancing.
The highly accurate current sensing and balancing
Quick-PWM Slave Controller with
Driver Disable for Multiphase DC-DC Converter
18
______________________________________________________________________________________
CC
voltage drops below 3.75V, it is assumed that
CC
rises above 3.75V, valid transitions
CC
Thermal-Fault Protection
LOAD
undervoltage lockout (UVLO)
Undervoltage Lockout
Design Procedure
= I
IN(MIN)
LOAD(MAX)
LOAD(MAX)
) must account for
) determines
✕
80%.
IN(MAX)
LOAD
)
)
implemented by the MAX1980 slave controller evenly
distributes the load among each phase:
where
Switching Frequency: This choice determines the
basic trade-off between size and efficiency. The opti-
mal frequency is largely a function of maximum input
voltage, due to MOSFET switching losses that are pro-
portional to frequency and V
cy also is a moving target, due to rapid improvements
in MOSFET technology that are making higher frequen-
cies more practical.
Setting Switch On Time: The constant on-time control
algorithm in the master results in a nearly constant
switching frequency despite the lack of a fixed-frequen-
cy clock generator. In the slave, the high-side switch on
time is inversely proportional to V+ and directly propor-
tional to the compensation voltage (V
where K is set by the TON pin-strap connection (Table 3).
Set the nominal on time in the slave to match the on
time in the master. An exact match is not necessary
because the MAX1980 have wide t
ranges (±40%). For example, if t
to 250kHz, the slave can be set to either 200kHz or
300kHz and still achieve good performance. Care
should be taken to ensure that the COMP voltage
remains within its output voltage range (0.42V to 2.80V).
Inductor Operating Point: This choice provides trade-
offs between size vs. efficiency and transient response
vs. output noise. Low inductor values provide better
transient response and smaller physical size, but also
result in lower efficiency and higher output noise due to
increased ripple current. The minimum practical induc-
tor value is one that causes the circuit to operate at the
edge of critical conduction (where the inductor current
just touches zero with every cycle at maximum load).
Inductor values lower than this grant no further size-
reduction benefit. The optimum operating point is usu-
ally found between 20% and 50% ripple current.
η
I
LOAD SLAVE
is the number of phases.
(
t
ON
)
=
=
I
LOAD MASTER
K



V
COMP
IN
V
(
IN
2
. The optimum frequen-
ON



in the master is set
COMP
)
=
ON
I
LOAD
):
η
adjustment