Rainbow Electronics MAX17036 - Manual (Page 23)

MAX17030/MAX17036
1/2/3-Phase Quick-PWM
IMVP-6.5 VID Controllers
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Current Limit
The current-limit circuit employs a unique “valley” cur-
rent-sensing algorithm that senses the voltage across
the current-sense resistors or inductor DCR at the cur-
rent-sense inputs (CSP_ to CSN_). If the current-sense
signal of the selected phase is above the current-limit
threshold, the PWM controller does not initiate a new
cycle until the inductor current of the selected phase
drops below the valley current-limit threshold. When
any one phase exceeds the current limit, all phases are
effectively current limited since the interleaved con-
troller does not initiate a cycle with the next phase.
Since only the valley current is actively limited, the actu-
al peak current is greater than the current-limit thresh-
old by an amount equal to the inductor ripple current.
Therefore, the exact current-limit characteristic and
maximum load capability are a function of the current-
sense resistance, inductor value, and battery voltage.
The positive valley current-limit threshold voltage at
CSP to CSN equals precisely 1/10 of the differential
TIME to ILIM voltage over a 0.1V to 0.5V range (10mV
to 50mV current-sense range). Connect ILIM directly to
V
CC to set the default current-limit threshold setting of
22.5mV (typ).
The negative current-limit threshold (forced-PWM mode
only) is nominally -125% of the corresponding valley
current-limit threshold. When the inductor current drops
below the negative current limit, the controller immedi-
ately activates an on-time pulse—DL turns off, and DH
turns on—allowing the inductor current to remain above
the negative current threshold.
Carefully observe the PCB layout guidelines to ensure
that noise and DC errors do not corrupt the current-sense
signals seen by the current-sense inputs (CSP_, CSN_).
Feedback Adjustment Amplifiers
Voltage-Positioning Amplifier
(Steady-State Droop)
The MAX17030/MAX17036 include a transconductance
amplifier for adding gain to the voltage-positioning sense
path. The amplifier’s input is generated by summing the
current-sense inputs, which differentially sense the volt-
age across either current-sense resistors or the induc-
tor’s DCR. The amplifier’s output connects directly to the
regulator’s voltage-positioned feedback input (FB), so
the resistance between FB and the output-voltage sense
point determines the voltage-positioning gain:
where the target voltage (V TARGET ) is defined in the
Nominal Output Voltage Selection section, and the FB
amplifier’s output current (I FB ) is determined by the
sum of the current-sense voltages:
where V CSX = V CSP - V CSN is the differential current-
sense voltage, and G m(FB) is typically 400µS as
defined in the Electrical Characteristics .
Differential Remote Sense
The MAX17030/MAX17036 include differential, remote-
sense inputs to eliminate the effects of voltage drops
along the PCB traces and through the processor’s
power pins. The feedback-sense node connects to the
voltage-positioning resistor (R
FB
). The ground-sense
(GNDS) input connects to an amplifier that adds an off-
set directly to the target voltage, effectively adjusting
the output voltage to counteract the voltage drop in the
ground path. Connect the voltage-positioning resistor
(R
FB ) and ground sense (GNDS) input directly to the
processor’s remote sense outputs as shown in Figure 1.
Integrator Amplifier
An internal integrator amplifier forces the DC average of
the FB voltage to equal the target voltage, allowing
accurate DC output-voltage regulation regardless of the
output ripple voltage.
The MAX17030/MAX17036 disable the integrator by
connecting the amplifier inputs together at the begin-
ning of all VID transitions done in pulse-skipping mode
(DPRSLPVR = high). The integrator remains disabled
until 20µs after the transition is completed (the internal
target settles) and the output is in regulation (edge
detected on the error comparator).
Transient Overlap Operation
When a transient occurs, the response time of the con-
troller depends on how quickly it can slew the inductor
current. Multiphase controllers that remain 120
° out-of-
phase when a transient occurs actually respond slower
than an equivalent single-phase controller. In order to
provide fast transient response, the MAX17030/
MAX17036 support a phase overlap mode, which
allows the triple regulators to operate in-phase when
heavy load transients are detected, effectively reducing
the response time. After any high-side MOSFET turns
off, if the output voltage does not exceed the regulation
voltage when the minimum off-time expires, the con-
troller simultaneously turns on all high-side MOSFETs
with the same on-time during the next on-time cycle.
The phases remain overlapped until the output voltage
exceeds the regulation voltage after the minimum
I G V
FB m FB CSX
X
PH
= ∑
=
( )
1
η
V V R I
OUT TARGET FB FB
= −