MAX16974EVKIT+ Maxim Integrated Products, MAX16974EVKIT+ Datasheet - Page 13

• 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

Figure 4. Switching Frequency vs. R
Assume a full 100mA is needed to refresh the BST
capacitor. Depending on the size of the inductor, the time
it takes to build up a full 100mA in the inductor is given by:
L = inductor value chosen in the design guide
di is the required current = 100mA
dV = voltage across the inductor (assume this to be
0.5V), which means V
If dt (inductor) < 7.65 - 6 (clock cycles), the BST capaci-
tor should be sized as follows:
dt (no load) = 7.65 clock cycles = 34.77µs
dV (BST capacitor) for (3.3V to 5V) output = V
(2.7V is the minimum voltage allowed on the bst capacitor)
If dt (inductor) > 7.65 - 6 clock cycles, then wait for the
next count of 3.65 clock cycles making dt (no load) =
11.65 clock cycles.
Considering the typical inductor values used for 220kHz
operation, the safe way to design the BST capacitor is
to assume:
So the final BST_CAPACITOR equation is:
dt (inductor) = L x di/dV (current buildup starts from the
BST_CAP = I
BST_CAP ≥ I
Down Converter with Low Operating Current
High-Voltage, 2.2MHz, 2A Automotive Step-
dt (no load) as 16 clock cycles
2.8
2.4
2.0
1.6
1.2
0.8
0.4
0
12
BST(DROPOUT)
______________________________________________________________________________________
SWITCHING FREQUENCY vs. R
22 32 42
BST(DROPOUT)
6th clock cycle)
(BST capacitor)
IN
capacitor)
is greater than V
52
R
62 72 82 92
FOSC
x dt (no load)/dV (BST
(k I )
FOSC
x dt (no load)/dV
102
112
FOSC
OUT
122
OUT
by 0.5V
- 2.7V
where
I
dt (no load) = 16 clock cycles
dV (BST capacitor) = V
The device offers a capacitor-adjustable reset timeout
period. Connect up to 0.1FF capacitor from CRES to
GND to set the timeout period. CRES can source 10FA
of current. Use the following formula to set the timeout
period:
where C is the capacitor from CRES to GND in Farads.
The switching frequency, f
(R
select the correct R
frequency.
For example, a 2.2MHz switching frequency is set with
R
with lower inductor values and less output capacitance.
Consequently, peak currents and I
at higher switching frequencies, but core losses, gate-
charge currents, and switching losses increase.
Three key inductor parameters must be specified for
operation with the device: inductance value (L), inductor
saturation current (I
select inductance value, the ratio of inductor peak-to-
peak AC current to DC average current (LIR) must be
selected first. A good compromise between size and
loss is a 30% peak-to-peak ripple current to average
current ratio (LIR = 0.3). The switching frequency, input
voltage, output voltage, and selected LIR determine the
inductor value as follows:
where V
efficiency is optimum for typical conditions. The switch-
ing frequency is set by R
section). The exact inductor value is not critical and can
be adjusted to make trade-offs among size, cost, effi-
ciency, and transient response requirements.
BST(DROPOUT)
FOSC
FOSC
) connected from FOSC to GND. See Figure 4 to
= 12.1kI. Higher frequencies allow designs
SUP
RESET_TIMEOUT
, V
OUT
L
= 3mA (worst case)
=
, and I
FOSC
V
SAT
OUT
V
SUP SW OUT
OUT
), and DC resistance (R
FOSC
(V
value for the desired switching
OUT
f
SUP
- 2.7V.
Reset Timeout Period
=
SW
I
(see the Internal Oscillator
are typical values so that
10 10 A
1.25V C
−
, is set by a resistor
Internal Oscillator
V
×
OUT
LIR
2
Inductor Selection
R losses are lower
×
-6
)
(s),
DCR
). To
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