MAX17020 Datasheet, PDF (23/34 Pages) Maxim Integrated Products – Dual Quick-PWM Step-Down Controller with Low-Power LDO, RTC Regulator

Dual Quick-PWM Step-Down Controller
with Low-Power LDO, RTC Regulator
Dynamic Output Voltage—OUT2 Only
The MAX17020 regulates OUT2 to the voltage set at
REFIN2, so the MAX17020 supports applications that
require dynamic output-voltage changes between two
set points by adjusting the REFIN2 voltage. For a step-
voltage change at REFIN2, the rate of change of the
output voltage is limited either by the internal slew-rate
circuit, by the REFIN2 slew rate, or by the component
selection—inductor current ramp, the total output
capacitance, the current limit, and the load during the
transition—whichever is the slowest. The total output
capacitance determines how much current is needed to
change the output voltage, while the inductor limits the
current ramp rate. Additional load current slows down
the output voltage change during a positive REFIN2
voltage change, and speeds up the output voltage
change during a negative REFIN2 voltage change.
Figure 5 is the dynamic REFIN transition.
Automatic Fault Blanking
When the MAX17020 automatically detects that the
internal target and REFIN2 are more than ±25mV (typ)
apart, the controller automatically blanks PGOOD2,
blanks the UVP protection, and sets the OVP threshold
to REF + 200mV. The blanking remains until 1) the inter-
nal target and REFIN2 are within ±20mV of each other
and 2) an edge is detected on the error amplifier signi-
fying that the output is in regulation. This prevents the
system or internal fault protection from shutting down
the controller during transitions.
Valley Current-Limit Protection
The current-limit circuit employs a unique “valley” cur-
rent-sensing algorithm that senses the inductor current
through the low-side MOSFET—across LX to AGND. 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 bat-
tery voltage. When combined with the undervoltage
protection circuit, this current-limit method is effective in
almost every circumstance.
In forced-PWM mode, the MAX17020 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.
POR, UVLO
When V_CC rises above the power-on reset (POR) thresh-
old, the MAX17020 clears the fault latches, forces the
low-side MOSFET to turn on (DL high), and resets the
soft-start circuit, preparing the controller for power-up.
However, the V_CC undervoltage lockout (UVLO) circuitry
inhibits switching until V_CC reaches 4.2V (typ). When
V_CC rises above 4.2V and the controller has been
enabled (ON_ pulled high), the controller activates the
enabled PWM controllers and initializes soft-start.
REFIN
OUTPUT
VOLTAGE
LX
PGOOD
OVP
20mV
BLANK HIGH-Z
REF + 140mV
±20mV WINDOW BETWEEN
INTERNAL TARGET AND REFIN2
INTERNAL EA TARGET = ACTUAL V_OUT
20mV
DYNAMIC REFIN WINDOW
EA TARGET + 140mV
BLANK HIGH-Z
EA TARGET + 140mV
Figure 5. Dynamic REFIN Transition
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