MAX17080GTL+ Maxim Integrated Products, MAX17080GTL+ Datasheet - Page 29

• Manufacturer Part Number: MAX17080GTL+
• Description: IC CONTROLLER AMD SVI 40-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX17080GTL+

• Applications: Controller, AMD SVI
• Voltage - Input: 2.7 ~ 5.5 V
• Number Of Outputs: 3
• Operating Temperature: -40°C ~ 105°C
• Mounting Type: Surface Mount
• Package / Case: 40-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -

Figure 5. VID Transition Timing
Each SMPS can be individually set to operate in pulse-
skipping mode when its PSI_L bit is set to 0, or set to
operate 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
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 MAX17080 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
LIMIT
GND
- V
for the core SMPS and I
LX
drops below the zero-crossing threshold,
PWRGD UPPER THRESHOLD
SMPS VOLTAGE
(SMPS TARGET)
Automatic Pulse-Skipping Crossover
SMPS LOAD
Idle-Mode Current-Sense Threshold
______________________________________________________________________________________
SVC/SVD
PWRGD
PWRGD LOWER
THRESHOLD
LX3MIN
HIGH-Z
BLANK
UPPER THRESHOLD BLANKED
= 0.25 x I
20µs
IDLE
AMD 2-/3-Output Mobile Serial
LIGHT LOAD
BUS IDLE
= 0.15 x
LX3PK
SMPS TARGET
BLANK
HIGH-Z
the driver forces DL low. This mechanism causes the
threshold between pulse-skipping PFM and nonskip-
ping PWM operation to coincide with the boundary
between continuous and discontinuous inductor-current
operation (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.
20µs
BUS IDLE
LOAD(SKIP)
I
LOAD SKIP
(
, is given by:
HIGH-Z
BLANK
VID Controller
)
=
20µs
V
OUT
HEAVY LOAD
Core SMPS Current Sense
BUS IDLE
2
(
V f
V
IN SW
IN
−
V
L
Current Sense
OUT
)
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