MAX6841IUKD3+T Maxim Integrated, MAX6841IUKD3+T Datasheet - Page 19

• Manufacturer Part Number: MAX6841IUKD3+T
• Description: Supervisory Circuits
• Manufacturer: Maxim Integrated
• Series: MAX6841, MAX6842, MAX6843, MAX6844, MAX6845r

Specifications of MAX6841IUKD3+T

• Number Of Voltages Monitored: 1
• Monitored Voltage: 0.9 V to 1.5 V
• Undervoltage Threshold: 1.35 V
• Overvoltage Threshold: 1.425 V
• Output Type: Active High, Active Low, Push-Pull
• Manual Reset: Resettable
• Watchdog: No Watchdog
• Battery Backup Switching: No Backup
• Power-up Reset Delay (typ): 280 ms
• Supply Voltage - Max: 1.8 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: SOT-23
• Chip Enable Signals: No
• Maximum Power Dissipation: 571 mW
• Minimum Operating Temperature: - 40 C
• Power Fail Detection: No
• Supply Current (typ): 8.1 uA
• Supply Voltage - Min: 0.75 V

(V
from stored inductor energy can be calculated as:
where I
The undershoot at the rising load edge of a load tran-
sient is calculated from:
where ΔI
4µs.
To ensure stability, make sure that the zero frequency
created by the output capacitance, and the ESR of the
output capacitor do not exceed 50kHz. The zero fre-
quency is found from:
Currently, aluminum electrolytic, Sanyo POSCAP, and
Panasonic SP capacitors have ESR zero frequencies
well below 50kHz. When using ceramic capacitors, it
might be necessary to use a series resistance to
ensure that the ESR zero is below 50kHz.
The input capacitor reduces peak currents drawn from
the power source and reduces noise and voltage ripple
on the input caused by the circuit’s switching. The input
capacitor must meet the ripple current requirement
(I
the following equation:
I
equals twice the output voltage (V
I
lum capacitors (ceramic, aluminum electrolytic, poly-
mer, or OS-CON) are preferred at the input because of
their robustness with high inrush currents typical of sys-
RMS(MAX)
RMS
V
RMS
SAG
SAG
) imposed by the switching currents as defined by
) is no longer a problem. The amount of overshoot
has a maximum value when the input voltage
=
PEAK
2
LOAD
I
RMS
×
= I
C
is the peak inductor current.
f
V
OUT
zESR
LOAD
SOAR
L
=
is the change in load current, and K is
× Δ
I
LOAD
×
______________________________________________________________________________________
=
I
2
2
V
/ 2. For most applications, nontanta-
=
LOAD
2π
OUT
2
Input Capacitor Selection
Controllers with Controlled VID Change
×
×
ESR
V
×
C
I
2
OUT
×
⎡
⎢
⎣
PEAK
OUT
Two-Phase Desktop CPU Core Supply
⎡
⎢
⎣
(
V
V
COUT
IN
OUT
×
1
×
V
−
(
V
×
IN
V
V
V
IN
V
L
IN
OUT
×
OUT
IN
×
K
C
−
V
IN
+
OUT
)
OUT
t
×
OFF MIN
= 2V
K
)
(
−
t
OFF MIN
OUT
)
⎤
⎥
⎦
(
), so
)
tems that may be powered from very low impedance
sources.
Multiple smaller value capacitors can be used in paral-
lel to satisfy the ESR and capacitance requirements.
The BST capacitors must be large enough to handle
the gate-charging requirements of the high-side
MOSFETs. For most applications, 0.22µF ceramic
capacitors are recommended.
BST capacitors are needed to keep the voltage on the
BST_ pins from dropping too much when the high-side
MOSFET gates are charged. A capacitor value that
prevents V
200mV is adequate. The capacitance needed for the
BST_ capacitor is calculated from:
where Q
MOSFET and ΔV
the BST_ pin drops when the gate is charged. If using
multiple MOSFETs in parallel, use the sum of all the
gate charges for Q
Current limit sets the maximum value of the inductor
“valley” current. I
equation:
The current-limit threshold (I
than the valley current:
The current-limit threshold is set by the voltage at ILIM
and the value of the current-sense resistors:
where V
and R
on-resistance of the low-side MOSFET is used for cur-
rent sensing, then the maximum value of the on-resis-
tance (overtemperature and part-to-part variation) must
be used for R
CS
ILIM
GH
is the value of the current-sense resistor. If the
I
VALLEY
BST
is the voltage on the ILIM pin (0.1V to 2V)
is the total gate charge of the high-side
CS
_ from dropping more than 100mV to
.
BST_
VALLEY
C
I
GH
=
LIMIT
BST
I
I
LIMIT
LOAD MAX
Selecting a BST Capacitor
.
is the amount that the voltage on
Setting the Current Limit
_
is calculated from the following
=
=
2
>
(
10
Δ
I
VALLEY
V
Q
V
×
LIMIT
ILIM
BST
GH
R
)
CS
×
_
⎛
⎜
⎝
) must be set higher
1
−
LIR
2
⎞
⎟
⎠
19