MAX16993 View Datasheet(PDF) - Maxim Integrated
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MAX16993
Step-Down Controller with
Dual 2.1MHz Step-Down DC-DC Converters
Table 2. Inductor Values vs. (VPV_, VOUT)
VPV_ TO VOUT (V)
INDUCTOR (µH), ILOAD = 1.5A
INDUCTOR (µH), ILOAD = 3.0A
VPV2/3 = 5.5V,
VOUT2/3 = 3.3V
2.2
1.0
VPV2/3 = 5.5V,
VOUT2/3 = 2.5V
1.5
0.68
VPV2/3 = 5.5V,
VOUT2/3 = 1.5V
1.0
0.56
VPV2/3 = 3.0V,
VOUT2/3 = 0.8V
0.56
0.33
Table 3. Output Capacitor Values vs. VOUT
VOUT (V) 3.3
2.5
1.5
0.8
COUT (µF), IMAX = 1.5A ≥ 12 ≥ 15 ≥ 25 ≥ 48
The next equation ensures that the inductor current down
slope is less than the internal slope compensation. For
this to be the case, the following equation needs to be
satisfied:
−m ≥ m2
2
-m
Slope compensation, [0.8 x VREF/(µs x GCS)]
m2
Inductor current downslope, [VOUT/L]
Solving for L:
L= MIN2
VOUT
×
1.6
⋅
µs
VREF
⋅
G CS
The equation that provides the bigger inductor value must
be chosed for proper operation.
LMIN = max(LMIN1, LMIN2)
The maximum inductor value recommended is twice the
chosen value from the above formula.
LMAX = 2 x LMIN
OUT2/OUT3 Input Capacitor
Place a single 4.7µF ceramic bypass capacitor on the
PV2 and PV3 inputs. Phase interleaving of the two low-
voltage buck converters contributes to a lower required
input capacitance by cancelling input ripple currents.
Place the bypass capacitors as close as possible to their
corresponding PV_ input to ensure the best EMI and jitter
performance.
OUT2 /OUT3 Output Capacitor
The minimum capacitor required depends on output volt-
age, maximum device current capability, and the error
amplifier voltage gain. Use the following formula to deter-
mine the required output capacitor value:
C OUT(MIN)
=
VREF ⋅ GCS ⋅ GEAMP
2π ⋅ fCO ⋅ VOUT
VREF
GCS
fCO
GEAMP
Reference voltage, VREF = 1.25V.
Internal current sense conductance. See the
Selector Guide for the value for each specific part
number.
GCS = 0.8S; for 1.5A output channels
GCS = 1.6S; for 3.0A output channels
Target crossover frequency, 250kHz.
Error amplifier voltage gain is 50V/V
GEAMP = 50V/V
where VREF is the crossover frequency.
Table 3 lists some of the capacitor values for 1.5A
output current and several output voltages. For prop-
er functionality, ceramic capacitors must be used.
Make sure that the self-resonance of the ceramic
capacitors at the converters’ output converter is above
1MHz to avoid instability.
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