MAX1956ETI Maxim Integrated Products, MAX1956ETI Datasheet - Page 12

• Manufacturer Part Number: MAX1956ETI
• Description: DC/DC Switching Controllers
• Manufacturer: Maxim Integrated Products

Specifications of MAX1956ETI

• Number Of Outputs: 2
• Output Voltage: 0.8 V to 4.95 V
• Input Voltage: 1.6 V to 5.5 V
• Package / Case: TQFN EP-28
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

1.6V to 5.5V Input, 0.5% Accurate, Dual
180° Out-of-Phase Step-Down Controllers
Foldback current limit is used to reduce power dissipa-
tion during overload and short-circuit conditions. This is
accomplished by lowering the current-limit threshold as
the output voltage drops because of overload.
To use foldback current limit, connect one resistor
(R
connect another resistor (R
values of R
1) First, select the percentage of foldback (P
2) Select P
The MAX1955/MAX1956 do not recover to nominal out-
put voltage at heavy load (near full load) after an over-
load or short-circuit condition, but they might operate at
a voltage below the nominal output until the input
power or EN pin is cycled through the OFF state. If
automatic recovery is mandatory, without cycling EN or
input power, add an RC filter of 1Ω and 0.015µF at
LX_’s pins, as shown in Figure 6. Doing so decreases
the efficiency by 2% to 3%, depending on the input
voltage, output voltage, and current.
Due to high switching frequency and tight output toler-
ance (±0.5%), decoupling between V
recommended. Connect a 10Ω resistor between V
and AV
GND. Place the capacitor as close to AV
When the voltage at IN drops below its undervoltage
lockout (UVLO) threshold (see the Electrical
Characteristics), the MAX1955/MAX1956 determine
that the input supply voltage is too low to power the IC.
12
R
FOBK
percentage corresponds to the current limit when
V
V
15% to 30%. To solve for the resistor values, use the
following equations:
zero.
ILIM
OUT
OUT
______________________________________________________________________________________
) from ILIM_ to the corresponding output, and
DD
Undervoltage Lockout (UVLO)
=
equals zero, divided by the current limit when
equals its nominal voltage. Typical values are
6 67
ILIM
and a 0.47µF capacitor between AV
V
FB
.
OUT
and R
values that provide R
×
R
-
R
FOBK
(
DS ON
6 67
.
FOBK
(
=
×
Recovery from Overload
)
R
Foldback Current Limit
×
are calculated as follows:
ILIM
P
5
DS ON
AV DD Decoupling
FB
µ
I
VALLEY
A
(
) from ILIM_ to GND. The
(
×
1
-
)
V
and Short Circuit
P
OUT
×
FB
I
×
VALLEY
)
ILIM
(
1
DD
DD
-
P
FB
and AV
greater than
as possible.
×
)
×
(
FB
1
R
DD
-
). This
P
FOBK
DD
FB
and
DD
)
)
is
In this event, the main outputs and the internal boost
regulator are disabled. The boost regulator starts up
again once the voltage at IN rises above the UVLO
threshold.
The MAX1955/MAX1956 use a digital soft-start to
reduce input inrush current during startup. In soft-start,
the output voltage is ramped up by increasing the FB_
regulation voltage in 80 steps of 10mV. Total soft-start
time is typically 4.27ms.
Some power supplies exhibit soft regulation during soft-
start. If the MAX1955/MAX1956 are powered from such
a power supply and enabled at or before power-up, the
input voltage might dip below the UVLO threshold, and
the output might not soft-start properly. To avoid such
issues, enable the MAX1955/MAX1956 after the input
supply has stabilized or add an RC filter to the IN pin of
the IC as shown in Figure 6. The value of R20 is ~510Ω,
and the value of capacitor C31 is from 1µF to 10µF,
depending on the startup characteristic of the input
power supply. The capacitor value is chosen to provide
power to the IC (100µA max) and keep it from falling
below the UVLO threshold during the input power-
supply dip.
The outputs can be set to power up at the same time,
or output 1 can be set to power up first and power
down last. Connect SEQ to GND for simultaneous
power up/down. Connect SEQ to IN to make output 1
power up first and power down last. Figure 3 is a timing
diagram.
If there is a fault condition (such as a short circuit) on
output 1 causing its voltage to drop below 90% of its
nominal regulation voltage, and SEQ is connected to
IN, then output 2 shuts down. Once the fault is cleared,
allowing the voltage on output 1 to rise above 90% of
its nominal regulation voltage, output 2 soft-starts and
powers up again.
Figure 3. Timing Diagram
4.27ms
Startup and Output Sequencing
SEQ = GND
4.27ms
OUT1
OUT2
EN
4.27ms
SEQ = IN
4.27ms