MAX16064 Datasheet, PDF (12/52 Pages) Maxim Integrated Products – ±0.3% Accurate, Quad, Power-Supply Controller with Active-Voltage Output Control and PMBus Interface

±0.3% Accurate, Quad, Power-Supply Controller with
Active-Voltage Output Control and PMBus Interface
MAX16064 Operating Modes
Reference Input (REFIN) Mode
Figure 3 shows how to connect a MAX16064 to the ref-
erence voltage input of a typical power supply, allowing
the MAX16064 to fully control the power-supply output
voltage. Connect a DACOUT_ of the MAX16064 to the
REFIN input of the power supply and connect the out-
put-voltage terminals of the power supply to the RS_+
and RS_- sense inputs of the MAX16064. The sensed
voltage on RS_+ and RS_- is filtered by an internal
200Ω resistor and an external capacitor connected to
RS_C, and is digitized by a 12-bit ADC that uses an
accurate internal reference voltage.
Normal operation begins as follows: upon receiving an
OPERATION ON command or a turn-on signal from
A3/CONTROL, the MAX16064 waits the programmed
t_{ON_DELAY} time, then switches on the associated
ENOUT_ output and ramps up the power-supply output
voltage to its target VOUT_COMMAND value precisely
in the programmed t_{ON_RISE} time. This facilitates easy
implementation of tracking of multiple output rails. On
reaching the target output voltage, the MAX16064 con-
tinuously monitors the power-supply output voltage
obtained at the RS_+ and RS_- inputs, and regulates it
to within ±0.3% by incrementing or decrementing the
DACOUT_ output 1 LSB (0.5mV) at a time. The
MAX16064 output-voltage correction rate is controlled
by MFR_MODE.1, VLTO, and DAC_ACT_CNT, as dis-
cussed in the ADC Conversion, Monitoring, and AVOC
Adjustment Rates section.
Once the requested target power-supply voltage is
reached, it can be margined up or down at a slew rate
programmed by the VOUT_TRANSITION_RATE para-
meter. To achieve this, the MAX16064 increments or
decrements the DACOUT_ output in a suitable number
of steps that depend on the programmed transition
rate. The number of steps is calculated from the
VOUT_SCALE_LOOP parameter, which must be set to
the ratio of the power-supply output voltage to the
power-supply reference voltage. This ratio is the same
as the voltage-divider ratio implemented on the power
supply from its output voltage node to the inverting
input of its error amplifier. This allows the MAX16064 to
correctly calculate the number of DACOUT steps and
voltage increments/decrements per step and thus
achieve the programmed rise time and transition time.
Since the reference voltage input is provided by the
MAX16064, the REFIN mode provides complete control
of the power supply in terms of soft-start, soft-stop, and
margining transitions.
Upon receiving an OPERATION OFF command or a
turn-off signal from A3/CONTROL, the MAX16064 waits
the programmed t_{OFF_DELAY} time, ramps the output
voltage down to zero in the programmed t_{OFF_FALL}
time, then deasserts the ENOUT_ output. Each of the
four power-supply converters has its own set of delay
parameters, so sequencing is accomplished by loading
different delay times for each power supply.
Feedback (FB) Mode
Some power-supply converters do not provide a refer-
ence input. In these applications, the feedback node
can be used instead. Connect a DACOUT_ output of
the MAX16064 to the feedback node (FB) through a
resistor R_FB as shown in Figure 5. In steady-state oper-
ation, the MAX16064 controls the power-supply voltage
as measured between RS_+ and RS_- to 0.3% accura-
cy by adjusting DACOUT_ 1 LSB at a time (0.5mV), up
and down as required. This mode of operation is
termed FB mode. Since the MAX16064 does not have
control over the power-supply error-amplifier reference
voltage, this mode relies on the power-supply soft-start
setting to implement the required soft-start time.
Upon receiving an OPERATION ON command or a
turn-on signal from A3/CONTROL, the MAX16064 waits
the programmed t_{ON_DELAY} time, turns on the ENOUT_
output, causing the power supply to ramp up its output
voltage to its target value. The soft-start time taken by
the power supply to ramp from zero to its commanded
output voltage should be entered into the MAX16064
with the t_{ON_RISE} parameter.
During t_{ON_RISE}, the MAX16064 maintains DACOUT_ in
a high-impedance state by keeping the S_ switches
open. This allows the voltage at DACOUT_ to equal that
of the FB node of the power supply. At the end of the
t_{ON_RISE} delay time, the internal DAC output voltage is
set to match the external voltage measured on
DACOUT_, and then the DACOUT_ switch S_ is closed.
The voltages on either side of the resistor R_FB should
be equal, or very close to equal. Under these condi-
tions, little or no current flows into the FB node from
DACOUT_ and no perturbations are introduced to the
output voltage. From this point on, the MAX16064
adjusts the voltage at DACOUT_ to provide accurate
output-voltage control. In FB mode, the user must sup-
ply t_{ON_DELAY} and t_{ON_RISE}. If those parameters are
not set (the default values are zero), S_ closes prema-
turely and causes the supply voltage to overshoot or
undershoot.
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