MAX17480GTL+ Maxim Integrated Products, MAX17480GTL+ Datasheet - Page 30

• Manufacturer Part Number: MAX17480GTL+
• Description: IC CTRLR SERIAL VID 40-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX17480GTL+

• Applications: Processor
• Current - Supply: 5mA
• Voltage - Supply: 4.5 V ~ 5.5 V
• Operating Temperature: -40°C ~ 105°C
• Mounting Type: Surface Mount
• Package / Case: 40-TQFN Exposed Pad
• Output Voltage Range: - 10 V to + 10 V
• Input Voltage Range: 4 V to 26 V
• Input Current: 5 mA
• Power Dissipation: 1778 mW
• Operating Temperature Range: - 40 C to + 105 C
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AMD 2-/3-Output Mobile Serial
VID Controller
depending on the external MOSFETs and switching fre-
quency. To maintain high efficiency under light load
conditions, the processor could switch the controller to a
low-power pulse-skipping control scheme.
During soft-start and in power-saving mode—when the
PSI_L bit is set to 0—the MAX17480 operates in pulse-
skipping mode. Pulse-skipping mode enables the driver’s
zero-crossing comparator, so the driver pulls its DL low
when “zero” inductor current is detected (V
0). This keeps the inductor from discharging the output
capacitors and forces the controller to skip pulses under
light load conditions to avoid overcharging the output.
In pulse-skipping operation, the controller terminates
the on-time when the output voltage exceeds the feed-
back threshold and when the current-sense voltage
exceeds the idle-mode current-sense threshold (V
= 0.15 x V
I
conditions, the continuous inductor current remains
above the idle-mode current-sense threshold, so the
on-time depends only on the feedback voltage thresh-
old. Under light load conditions, the controller remains
above the feedback voltage threshold, so the on-time
duration depends solely on the idle-mode current-
sense threshold, which is approximately 15% of the full-
load peak current-limit threshold set by ILIM12 for the
core SMPSs and 25% of the full-load peak current-limit
threshold set by ILIM3 for the NB SMPS.
During downward VID transitions, the controller tem-
porarily sets the OVP threshold of the SMPSs to 1.85V
(typ), preventing false OVP faults. Once the error ampli-
fier detects that the output voltage is in regulation, the
OVP threshold tracks the selected VID DAC code.
Each SMPS can be individually set to operate in pulse-
skipping mode when its PSI_L bit is set to 0, or set to oper-
ate in forced-PWM mode when its PSI_L bit is set to 1.
When the core SMPSs are configured for combined-
mode operation, core supplies operate in 1-phase
pulse-skipping mode when PSI_L = 0, and core sup-
plies are in 2-phase forced-PWM mode when PSI_L = 1.
The idle-mode current-sense threshold forces a lightly
loaded SMPS to source a minimum amount of power
with each on-time since the controller cannot terminate
the on-time until the current-sense voltage exceeds the
idle-mode current-sense threshold (V
V
setting for the NB SMPS). Since the zero-crossing com-
parator prevents the switching SMPS from sinking
30
LX3PK
LIMIT
______________________________________________________________________________________
for the core SMPS and I
setting for the NB SMPS). Under heavy load
LIMIT
for the core SMPS and I
Idle-Mode Current-Sense Threshold
Pulse-Skipping Operation
LX3MIN
= 0.25 x I
LX3MIN
IDLE
GND
= 0.15 x
= 0.25 x
- V
LX3PK
LX
IDLE
=
current, the controller must skip pulses to avoid over-
charging the output. When the clock edge occurs, if the
output voltage still exceeds the feedback threshold, the
controller does not initiate another on-time. This forces
the controller to actually regulate the valley of the out-
put voltage ripple under light load conditions.
In skip mode, the MAX17480 zero-crossing compara-
tors are active. Therefore, an inherent automatic
switchover to PFM takes place at light loads, resulting in
a highly efficient operating mode. This switchover is
affected by a comparator that truncates the low-side
switch on-time at the inductor current’s zero crossing.
The driver’s zero-crossing comparator senses the
inductor current across the low-side MOSFET. Once
V
the driver forces DL low. This mechanism causes the
threshold between pulse-skipping PFM and nonskipping
PWM operation to coincide with the boundary between
continuous and discontinuous inductor-current opera-
tion (also known as the critical conduction point). The
load-current level at which the PFM/PWM crossover
occurs, I
The switching waveforms can appear noisy and asyn-
chronous when light loading causes pulse-skipping
operation, but this is a normal operating condition that
results in high light-load efficiency. Trade-off in PFM
noise vs. light-load efficiency is made by varying the
inductor value. Generally, low inductor values produce a
broader efficiency vs. load curve, while higher values
result in higher full-load efficiency (assuming that the coil
resistance remains fixed) and less output voltage ripple.
Penalties for using higher inductor values include larger
physical size and degraded load-transient response
(especially at low input-voltage levels).
The output current of each phase is sensed differentially.
A low offset voltage and high-gain differential current
amplifier at each phase allows low-resistance current-
sense resistors to be used to minimize power dissipa-
tion. Sensing the current at the output of each phase
offers advantages, including less noise sensitivity, more
accurate current sharing between phases, and the flex-
ibility of using either a current-sense resistor or the DC
resistance of the output inductor.
GND
- V
LOAD(SKIP)
LX
I
LOAD SKIP
drops below the zero-crossing threshold,
Automatic Pulse-Skipping Crossover
(
, is given by:
)
=
V
OUT
Core SMPS Current Sense
2
(
V f
V
IN SW
IN
−
V
L
Current Sense
OUT
)