MAX17009 Datasheet, PDF (22/45 Pages) Maxim Integrated Products – AMD Mobile Serial VID Dual-Phase Fixed-Frequency Controller

AMD Mobile Serial VID Dual-Phase
Fixed-Frequency Controller
Interleaved Multiphase Operation
The MAX17009 interleaves both phases—resulting in
180° out-of-phase operation that minimizes the input and
output filtering requirements, reduces electromagnetic
interference (EMI), and improves efficiency. The high-
side MOSFETs do not turn on simultaneously during nor-
mal operation. The instantaneous input current is
effectively reduced by the number of active phases,
resulting in reduced input-voltage ripple, ESR power loss,
and RMS ripple current (see the Input-Capacitor
Selection section). Therefore, the controller achieves high
performance while minimizing the component count,
which reduces cost, saves board space, and lowers
component power requirements, making the MAX17009
ideal for high-power, cost-sensitive applications.
Transient-Phase Repeat
When a transient occurs, the output-voltage deviation
depends on the controller’s ability to quickly detect the
transient and slew the inductor current. A fixed-fre-
quency controller typically responds only when a clock
edge occurs, resulting in a delayed transient response.
To minimize this delay time, the MAX17009 includes
enhanced transient detection and transient- phase-
repeat capabilities. If the controller detects that the out-
put voltage has dropped by 25mV, the transient-
detection comparator immediately retriggers the phase
that completed its on-time last. The controller triggers
the subsequent phases as normal on the appropriate
oscillator edges. This effectively triggers a phase a full
cycle early, increasing the total inductor-current slew
rate and providing an immediate transient response.
The OPTION pin setting enables or disables the tran-
sient phase-repeat feature. Keep OPTION OPEN or
connected to GND to enable transient-phase repeat.
Connect OPTION to V_CC or REF to disable transient-
phase repeat. See the Offset and Transient-Phase
Repeat (OPTION) section.
Feedback Adjustment Amplifiers
Steady-State Voltage-Positioning
Amplifier (DC Droop)
Each of the MAX17009 SMPS controllers includes two
transconductance amplifiers—one for steady-state DC
droop, and another for AC droop. The amplifiers’ inputs
are generated by summing their respective current-sense
inputs, which differentially sense the voltage across either
current-sense resistors or the inductor’s DCR.
The DC droop amplifier’s output (FBDC) connects to
the remote-sense point of the output through a resistor
that sets each phase’s DC voltage-positioning gain:
V_OUT = V_TARGET − R_FBDCI_FBDC
where the target voltage (V_TARGET) is defined in the
Nominal Output-Voltage Selection section, and the
FBDC amplifier’s output current (I_FBDC) is determined
by each phase’s current-sense voltage:
I_FBDC = G_m(FBDC)V_CS
where V_CS = V_CSP - V_CSN is the differential current-
sense voltage, and G_M(FBDC) is typically 1mS as
defined in the Electrical Characteristics table.
DC droop is typically used together with the +12.5mV
offset feature to keep within the DC tolerance window of
the application. See the Offset and Transient-Phase
Repeat (OPTION) section. The ripple voltage on FBDC
must be less than the 18mV (min) transient phase
repeat threshold:
ΔI_LR_SENSEG_m(FBDC)R_FBDC + ΔI_LR_ESR ≤ 18mV
R_FBDC
≤
⎛ 18mV
⎝⎜ ΔI_L
− R_ESR^{⎞⎠⎟}
− R_SENSEG_m(FBDC)
where ΔI_L is the inductor ripple current, R_ESR is the
effective output ESR at the remote sense point, R_SENSE is
the current-sense element, and G_m(FBDC) is 1.03mS
(max) as defined in the Electrical Characteristics table.
The worst-case inductor ripple occurs at the maximum
input voltage and the minimum output-voltage conditions:
( ) _ΔIL(MAX)
=
V_OUT(MIN) V_IN(MAX) − V_OUT(MIN)
V_IN(MAX)f_OSCL
To disable voltage positioning, set R_FBDC to zero.
Transient Voltage-Positioning Amplifier (AC Droop)
The AC droop amplifier’s output (FBAC) connects to
the remote-sense point of the output through a resistor
that sets each phase’s AC voltage-positioning gain:
V_OUT = V_TARGET − R_FBACI_FBAC
where the target voltage (V_TARGET) is defined in the
Nominal Output-Voltage Selection section, and the
FBAC amplifier’s output current (I_FBAC) is determined
by each phase’s current-sense voltage:
I_FBAC = G_m(FBAC)V_CS
where V_CS = V_CSP - V_CSN is the differential current-
sense voltage, and G_M(FBAC) is 1.03mS (max), as
defined in the Electrical Characteristics table.
AC droop is required for stable operation of the
MAX17009. A minimum of 1mV/A is recommended. AC
droop must not be disabled.
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