MAX15569 Datasheet, PDF (15/41 Pages) Maxim Integrated Products – 2-Phase/1-Phase QuickTune-PWM Controller with Serial I2C Interface

MAX15569
2-Phase/1-Phase QuickTune-PWM Controller with
Serial I²C Interface
Detailed Description
For system power management, the MAX15569
controller includes a current gauge and thermal status
(VRHOT) that can be monitored over the I²C interface.
In addition, the device’s multiple fault-protection fea-
tures include: Output overvoltage protection (OVP),
undervoltage protection (UVP), and thermal protection.
When any of these fault-protection features detect a
fault condition, the controller shuts down.
Free-Running Constant On-Time Controller
with Input Feed-Forward
The QuickTune-PWM control architecture consists of a
pseudofixed frequency, constant on-time, and current-
mode regulator with voltage feed-forward (Figure 2). The
control algorithm is simple; the high-side switch on-time is
determined solely by a one-shot, whose period is inversely
proportional to input voltage and directly proportional to
the feedback voltage or the difference between the main
and secondary inductor currents (see the On-Time One-
Shot section). Another one-shot sets a minimum off-time.
The on-time one-shot triggers when the inverting input
to the error comparator falls below the target voltage,
the inductor current of the selected phase is below the
valley current-limit threshold, and the minimum off-time
one-shot times out. The regulator maintains 180° out-of-
phase operation by alternately triggering the two phases
after the error comparator drops below the output-voltage
set point.
Switching Frequency
Connect a resistor (R_TON) between TON and the input
supply (V_IN) to set the switching period (t_SW = 1/f_SW) per
phase using the following equation:
t_SW (R_TON + 6.5kΩ) x 5pF
High-frequency (600kHz to 1.4MHz) operation optimizes
the application for the smallest component size. A 200kΩ
resistor sets a typical operating frequency of 1MHz.
On-Time One-Shot
The device contains fast, low-jitter, adjustable one-shots
that set the respective high-side MOSFET on-times
through the DRVPWM_ outputs. The one-shot for the
main phase varies the on-time in response to the input
and feedback voltage (V_FB). V_FB equals the SETVOUT
voltage in steady-state. The main high-side switch
on-time is inversely proportional to the input voltage as
measured at V_IN, and proportional to V_FB:
t _ON
=
t _SW (V_FB+ 0.075V)
V_IN
(Ignoring
propagation
delays)
For SETVOUT voltages below 0.9V, the device uses a
fixed 0.9V instead to determine the on-time. Switching
frequency is reduced, improving low-voltage efficiency.
t
ON
=
t
SW
(0.9V + 0.075V)
V_IN
The one-shot for the second phase varies the on-time in
response to the input voltage and the difference between
the main and the second inductor currents. Two identi-
cal transconductance amplifiers integrate the difference
between the first and second current-sense signals. The
respective error signals are used to correct the on-time
of the high-side MOSFETs for the second phase and to
maintain current balanced between the two phases.
On-times translate only roughly to switching frequencies.
The on-times guaranteed in the Electrical Characteristics
section are influenced by parasitics in the conduction
paths and propagation delays. The following equation
shows the effect of the propagation delays on t_ON:
t
ON⁼
t
SW
(V_FB+ 0.075V)₊
V_IN
t
D(OFF)
-
t
D(ON)
where t_D(OFF) is the delay from the falling edge of the PWM
signal to the to the time that the high-side MOSFET turns
off. t_D(ON) is the delay from the rising edge of the PWM
signal to the time that the high-side MOSFET turns on.
For loads above the critical conduction point, where the
dead-time effect (LX flying high and conducting through
the high-side FET body diode) is no longer a factor, the
actual switching frequency (per phase) is:
f_SW
=
(V_OUT + V_DIS )
t _ON(V_IN + V_DIS + V_CHG)
where V_DIS is the sum of the parasitic voltage drops in the
inductor discharge and charge paths, including MOSFET,
inductor, and PCB resistances; V_CHG is the sum of the
parasitic voltage drops in the inductor charge path, includ-
ing high-side switch, inductor, and PCB resistances; and
t_ON is the on-time as determined in the prior equation.
180° Out-of-Phase Operation
The two phases in the device operate 180° out-of-phase
to minimize input and output filtering requirements,
reduce EMI, and improve efficiency. This effectively low-
ers component count—reducing cost, board space, and
component power requirements—making this device
ideal for high-power applications. The device shares the
current between two phases that operate 180° out-of-
phase under steady-state conditions.
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