Manual

MAX17101
Dual Quick-PWM, Step-Down Controller
with Low-Power LDO, RTC Regulator
______________________________________________________________________________________ 23
Adjustable/Fixed Output Voltages
Connect FB1 to GND for fixed 5V operation. Connect FB1
to V
CC
for fixed 1.5V operation. Connect FB1 to an exter-
nal resistive voltage-divider from OUT1 to analog ground
to adjust the output voltage between 0.7V and 5.5V.
During soft-shutdown, application circuits configured for
adjustable feedback briefly switch modes when FB1
drops below the 110mV dual-mode threshold.
Choose R
FBL
(resistance from FB1 to AGND) to be
approximately 49.9kΩ and solve for R
FBH
(resistance
from OUT1 to FB1) using the following equation:
Connect REFIN2 to V
CC
for fixed 3.3V operation.
Connect REFIN2 to RTC (3.3V) for fixed 1.05V operation.
Connect REFIN2 to an external resistive voltage-divider
from REF to analog ground to adjust the output voltage
between 0.8V and 2V.
Choose R
REFINL
(resistance from REFIN2 to GND) to
be approximately 49.9kΩ and solve for R
REFINH
(resis-
tance from REF to REFIN2) using the equation:
Power-Good Outputs (PGOOD)
and Fault Protection
PGOOD is the open-drain output that continuously
monitors the output voltage for undervoltage and over-
voltage conditions. PGOOD_ is actively held low in
shutdown (ON_ = GND), during soft-start or soft-shut-
down. Approximately 20μs (typ) after the soft-start
terminates, PGOOD_ becomes high impedance as long
as the feedback voltage exceeds 85% of the nominal
fixed-regulation voltage or within 150mV of the REFIN2
input voltage. PGOOD_ goes low if the feedback volt-
age drops 16% below the fixed target voltage, or if the
output voltage drops 150mV below the dynamic REFIN2
voltage, or if the SMPS controller is shut down. For a
logic-level PGOOD_ output voltage, connect an external
pullup resistor between PGOOD_ and V
DD
. A 100kΩ
pullup resistor works well in most applications.
Overvoltage Protection (OVP)
When the output voltage rises 16% above the regula-
tion voltage, the controller immediately pulls the
respective PGOOD_ low, sets the overvoltage fault
latch, and immediately pulls the respective DL_ high—
clamping the output to GND. Toggle either ON1 or ON2
input, or cycle V
CC
power below its POR threshold to
clear the fault latch and restart the controller.
Undervoltage Protection (UVP)
When the output voltage drops 30% below the regula-
tion voltage, the controller immediately pulls the respec-
tive PGOOD_ low, sets the undervoltage fault latch, and
begins the shutdown sequence. After the output volt-
age drops below 0.1V, the synchronous rectifier turns
on, clamping the output to GND. Toggle either ON1 or
ON2 input, or cycle V
CC
power below its POR threshold
to clear the fault latch and restart the controller.
Thermal-Fault Protection (T
SHDN
)
The MAX17101 features a thermal-fault protection circuit.
When the junction temperature rises above +160°C, a
thermal sensor activates the fault latch, pulls PGOOD1
and PGOOD2 low, enables the 10Ω discharge circuit,
and disables the controller—DH and DL pulled low.
Toggle ONLDO or cycle IN power to reactivate the con-
troller after the junction temperature cools by 15°C.
RR
V
V
REFINH REFINL
REF
OUT
=−
⎛
⎝
⎜
⎞
⎠
⎟
2
1
RR
V
V
FBH FBL
OUT
=−
⎛
⎝
⎜
⎞
⎠
⎟
1
07
1
.
MODE CONTROLLER STATE DRIVER STATE
Shutdown (ON_ = High to Low);
Output UVP (Latched)
Voltage soft-shutdown initiated. Internal error-amplifier target
slowly ramped down to GND and output actively discharged
(automatically enters forced-PWM mode).
DL driven high and DH pulled
low after soft-shutdown
completed (output < 0.1V).
Output OVP (Latched)
Controller shuts down and EA target internally slewed down.
Controller remains off until ON_ toggled or V
CC
power cycled.
DL immediately driven high,
DH pulled low.
V
CC
UVLO Falling-Edge
Thermal Fault (Latched)
SMPS controller disabled (assuming ON_ pulled high), 10
output discharge active.
DL and DH pulled low.
V
CC
UVLO Rising Edge SMPS controller enabled (assuming ON_ pulled high). DL driven high, DH pulled low.
V
CC
POR SMPS inactive, 10 output discharge active. DL driven high, DH pulled low.
Table 4. Fault Protection and Shutdown Operation Table