MAX16975 View Datasheet(PDF) - Maxim Integrated
Part Name
Description
MFG CO.
MAX16975 Datasheet PDF : 17 Pages
| |||
MAX16975
28V, 1.2A Automotive Step-Down Converter
with Low Operating Current
RESETI
MAX16975
FB
VOUT
RFB1
RFB2
RFB3
Figure 1. Output Voltage/Reset Threshold Resistive Divider
Network
Overvoltage Protection
The device includes overvoltage protection circuitry that
protects the device when there is an overvoltage condi-
tion at the output. If the output voltage increases by more
than 12% of its set voltage, the device stops switching.
The device resumes regulation once the overvoltage
condition is removed.
Overload Protection
The overload protection circuitry is activated when the
device is in current limit and VOUT is below the reset
threshold. Under these conditions, the device enters
a soft-start mode. When the overcurrent condition is
removed before the soft-start mode is over, the device
regulates the output voltage to the set value. Otherwise,
the soft-start cycle repeats until the overcurrent condition
is removed.
Skip Mode
During light-load operation, IINDUCTOR P 200mA, the
device enters skip-mode operation. Skip mode turns off
the internal switch and allows the output to drop below
regulation voltage before the switch is turned on again.
The lower the load current, the longer it takes for the
regulator to initiate a new cycle effectively increasing
light-load efficiency. During skip mode, the device qui-
escent current drops to as low as 45FA.
Overtemperature Protection
Thermal-overload protection limits the total power dis-
sipation in the device. When the junction temperature
exceeds +175NC (typ), an internal thermal sensor shuts
down the step-down controller, allowing the device to
cool. The thermal sensor turns on the device again after
the junction temperature cools by +15NC.
Applications Information
Output Voltage/Reset Threshold
Resistive Divider Network
Although the device’s output voltage and reset threshold
can be set individually, Figure 1 shows a combined resis-
tive divider network to set the desired output voltage and
the reset threshold using three resistors. Use the follow-
ing formula to determine the RFB3 of the resistive divider
network:
R FB3
=
R TOTAL × VREF
V OUT
where VREF = 1V, RTOTAL = selected total resistance of
RFB1, RFB2, and RFB3 in ohms, and VOUT is the desired
output voltage in volts.
Use the following formula to calculate the value of RFB2
of the resistive divider network:
RFB2 =
R TOTAL × VREF_RES
V RES
−
RFB3
where VREF_RES is 1.25V (see the Electrical Characteristics
table) and VRES is the desired reset threshold in volts.
The precision of the reset threshold function is depen-
dent on the tolerance of the resistors used for the divider.
BST Capacitor Selection
for Dropout Operation
The device includes an internal boost capacitor refresh
algorithm for dropout operation. This is required to ensure
proper boost capacitor voltage that delivers power to the
gate-drive circuitry. When the HSFET is on consecutively
for 3.65 clock cycles, the internal counter detects this
and turns off the HSFET for 0.35 clock cycles. This is of
particular concern when VIN is falling and approaching
VOUT at the minimum switching frequency (220kHz).
The worst-case condition for boost capacitor refresh time
is with no load on the output. For the boost capacitor
to recharge completely, the LX node must be pulled to
ground. If there is no current through the inductor then
the LX node does not go to ground. To solve this issue,
an internal load of about 100mA turns on at the sixth
clock cycle, which is determined by a separate counter.
In the worst-case condition with no load, the LX node
does not go below ground during the first detect of the
���������������������������������������������������������������� Maxim Integrated Products 11
Share Link: 