MAX15035 Datasheet, PDF (17/27 Pages) Maxim Integrated Products – 15A Step-Down Regulator with Internal Switches

15A Step-Down Regulator with Internal Switches
REFIN
DYNAMIC REFIN WINDOW
OUTPUT
VOLTAGE
INTERNAL
PWM CONTROL
LX
PGOOD
OVP
PWM
BLANK HIGH-Z
SET TO REF +
300mV
INTERNAL EA TARGET = ACTUAL V_OUT
SKIP
PWM
SKIP
EA TARGET + 300mV
BLANK HIGH-Z
EA TARGET + 300mV
DYNAMIC TRANSITION WHEN SKIP = REF
Figure 5. Dynamic Transition when SKIP = REF
Valley Current-Limit Protection
The current-limit circuit employs a unique “valley”
current-sensing algorithm that senses the inductor
current through the low-side MOSFET. If the current
through the low-side MOSFET exceeds the valley
current-limit threshold, the PWM controller is not
allowed to initiate a new cycle. The actual peak current
is greater than the valley current-limit threshold by an
amount equal to the inductor ripple current. Therefore,
the exact current-limit characteristic and maximum load
capability are a function of the inductor value and input
voltage. When combined with the undervoltage protec-
tion circuit, this current-limit method is effective in
almost every circumstance.
In forced-PWM mode, the MAX15035 also implements
a negative current limit to prevent excessive reverse
inductor currents when V_OUT is sinking current. The
negative current-limit threshold is set to approximately
120% of the positive current limit.
Integrated Output Voltage
The MAX15035 regulates the valley of the output ripple,
so the actual DC output voltage is higher than the slope-
compensated target by 50% of the output ripple voltage.
Under steady-state conditions, the MAX15035’s internal
integrator corrects for this 50% output ripple-voltage
error, resulting in an output voltage that is dependent
only on the offset voltage of the integrator amplifier pro-
vided in the Electrical Characteristics table.
Dynamic Output Voltages
The MAX15035 regulates FB to the voltage set at REFIN.
By changing the voltage at REFIN (Figure 1), the
MAX15035 can be used in applications that require
dynamic output-voltage changes between two set
points. For a step-voltage change at REFIN, the rate of
change of the output voltage is limited either by the
internal 9.45mV/µs slew-rate circuit or by the component
selection—inductor current ramp, the total output
capacitance, the current limit, and the load during the
transition—whichever is slower. The total output capaci-
tance determines how much current is needed to
change the output voltage, while the inductor limits the
current ramp rate. Additional load current may slow
down the output voltage change during a positive REFIN
voltage change, and may speed up the output voltage
change during a negative REFIN voltage change.
______________________________________________________________________________________ 17