MAX16974EVKIT+ Maxim Integrated Products, MAX16974EVKIT+ Datasheet - Page 12

• Manufacturer Part Number: MAX16974EVKIT+
• Description: Power Management Modules & Development Tools MAX16974 EVAL KIT MAX16974 EVAL KIT
• Manufacturer: Maxim Integrated Products

Specifications of MAX16974EVKIT+

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

High-Voltage, 2.2MHz, 2A Automotive Step-
Down Converter with Low Operating Current
During light-load operation, I
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. Because the con-
verter skips unnecessary cycles, the converter efficiency
increases. During skip mode the quiescent current drops
to 35FA.
Thermal-overload protection limits the total power dissipa-
tion in the device. When the junction temperature exceeds
+175°C (typ), an internal thermal sensor shuts down the
internal bias regulator and the step-down controller, allow-
ing the IC to cool. The thermal sensor turns on the device
again after the junction temperature cools by +15°C.
Although the device’s output voltage and reset thresh-
old can be set individually, Figure 3 shows a combined
resistive divider network to set the desired output voltage
and the reset threshold using three resistors. Use the
following formula to determine the R
divider network:
where V
R
output voltage in volts.
where V
table), and V
The precision of the reset threshold function is dependent
on the tolerance of the resistors used for the divider. Care
must be taken to choose the values of the resistors. Too
small a resistor value adds to the device’s quiescent cur-
rent, whereas if the resistors are too large, there is some
noise susceptibility to the FB pin.
12
FB1
_____________________________________________________________________________________
, R
FB2
REF_RES
REF
R
, and R
FB2
= 1V, R
RES
Output Voltage/Reset Threshold
R
Applications Information
=
is 1.2V (see the Electrical Characteristics
FB3
is the desired reset threshold in volts.
FB3
R
Overtemperature Protection
TOTAL
TOTAL
=
Resistive Divider Network
in ohms, and V
R
TOTAL
V
= selected total resistance of
×
RES
V
V
INDUCTOR
REF_RES
OUT
×
V
REF
FB3
OUT
- R
of the resistive
P 240mA, the
is the desired
FB3
Skip Mode
Figure 3. Output Voltage/Reset Threshold Resistive Divider
Network
The device has an internal boost capacitor refresh algo-
rithm for dropout operation. This is required to ensure
proper boost capacitor voltage, which delivers power to
the gate drive circuitry. If the high-side MOSFET is on
consecutively for 3.65 clock cycles, the internal counter
detects this and turns off the high-side MOSFET for 0.35
clock cycles. This is of particular concern when V
falling and approaching V
frequency of 220kHz is used.
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 in the inductor, the LX node
does not go to ground. To solve this issue, an internal
load of approximately 100mA is turned on at the 6th
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
3.65 clock cycles. It must wait for the next 3.65 clock
cycles to finish. This means the soonest the LX node can
go below ground is 4 + 3.65 = 7.65 clock cycles. This
time does not factor in the size of the inductor and the
time it takes for the inductor current to build up to 100mA
(internal load).
So no-load minimum time before refresh is:
dt (no load) = 7.65 clock cycles = 7.65 x 5µs
MAX16974
(at 220kHz) = 34.77µs
RESETI
OUT
FB
and a minimum switching
Boost Capacitor for
Dropout Operation
R
R
R
FB1
FB2
FB3
V
OUT
IN
is