MAX16046A Datasheet, PDF (61/71 Pages) Maxim Integrated Products – 12-Channel/8-Channel EEPROM-Programmable System Managers with Nonvolatile Fault Registers

12-Channel/8-Channel EEPROM-Programmable
System Managers with Nonvolatile Fault Registers
Set the DACOUT_ range bits (see the DAC Outputs
section) such that V_REF falls approximately halfway
within the DACOUT range. Set R₅ to vary the amount of
control the DAC has on the output voltage of the power
supply. Large values of R₅ correspond to higher
degree of resolution control over the output voltage,
and small values of R₅ correspond to lesser degree of
resolution control. Be sure to respect the minimum and
maximum output voltages that the DC-DC converter is
capable of generating.
The following is an example that illustrates the use of
the formulas for calculating the margin up and margin
down values. This example uses a generic 3.3V DC-DC
converter with a trim input. Below are the margin up
and margin down formulas taken from the data sheet
for the power supply:
TRIM
DOWN:R _{ADJ_DOWN}
=
⎛
⎝⎜
100
Δ%
−
2 ^{⎞⎠⎟}
(kΩ)
TRIM UP:R _{ADJ_UP} =
⎛ V_{OUT_NOM} (100 +
⎝⎜
1.225Δ%
Δ%)
−
100 + 2Δ%
Δ%
⎞
⎠⎟
(kΩ
)
By inspecting these formulas, V_REF = 1.225V, R₃ =
1kΩ, and R₄ = 1kΩ. Set the DACOUT_ range from 0.8V
to 1.6V to fit the reference voltage. The output voltage
of the DC-DC converter is 3.3V; therefore the ratio (1 +
R₁/R₂) = V_OUT/V_REF = 3.3/1.225 = 2.69.
Set R₅ to zero to use the widest trim range possible
(increase R₅ to decrease the trim range). Insert these
values into the equations for the output voltage:
( ) _VOUT
=
( 2.69 ) ^{⎛⎝⎜}
1kΩ
×
V_DACOUT + 1kΩ
2kΩ
× 1.225 ⎞
⎠⎟
=
(2.69)
V_{DACOUT_} + 1.225
2
For V_{DACOUT_} = 0.8V, V_OUT = 2.72V, and for
V_{DACOUT_} = 1.6V, V_OUT = 3.80V. These output volt-
ages correspond with a margin down limit of -17.6%
and a margin up limit of 15.2%. Since the reference
voltage is not exactly in the center of the DACOUT_
range, the margin limits are not symmetrical. To
decrease the margin limits, increase the value of R₅.
Maintaining Power During a Fault
Condition
Power to the MAX16046A/MAX16048A must be main-
tained for a specific period of time to ensure a success-
ful EEPROM fault log operation during a fault that
removes power to the circuit. The amount of time
required depends on the settings in the fault control
register (r47h[1:0]) according to Table 36.
DC-DC OR LDO
OUT
R₁
R₅
R₂
R₃
R_{4 TRIM}
V_REF
MAX16046A
MAX16048A
V_{DACOUT_}
Figure 17. Connections for Margining Using Trim Input Method
Table 36. EEPROM Fault Log Operation
Period
FAULT CONTROL
REGISTER VALUE
r47h [1:0]
DESCRIPTION
REQUIRED
PERIOD
t_{FAULT_SAVE}
(ms)
00
Failed lines and
306
ADC values saved
01
Failed lines saved
90
10
ADC values saved
252
11
No information
saved
—
Maintain power for shutdown during fault conditions in
applications where the always-on power supply cannot
be relied upon by placing a diode and a large capaci-
tor between the voltage source, V_IN, and V_CC (Figure
18). The capacitor value depends on V_IN and the time
delay required, t_{FAULT_SAVE}. Use the following formula
to calculate the capacitor size:
C = ^{tFAULT_SAVE × ICC(MAX)}
V_IN − V_DIODE − V_UVLO
where the capacitance is in Farads and t_{FAULT_SAVE} is
in seconds. I_CC(MAX) is 6.5mA, V_DIODE is the voltage
drop across the diode, and V_UVLO is 2.85V. For exam-
ple, with a V_IN of 14V, a diode drop of 0.7V, and a
t_{FAULT_SAVE} of 0.306s, the minimum required capaci-
tance is 190μF.
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