LMZ10504TZ-ADJ/NOPB National Semiconductor, LMZ10504TZ-ADJ/NOPB Datasheet - Page 12

• Manufacturer Part Number: LMZ10504TZ-ADJ/NOPB
• Description: IC BUCK SYNC ADJ 4A TO-PMOD-7
• Manufacturer: National Semiconductor
• Series: SIMPLE SWITCHER®r
• Type: Point of Load (POL) Non-Isolated with UVLOr

Specifications of LMZ10504TZ-ADJ/NOPB

• Output: 0.8 ~ 5 V
• Number Of Outputs: 1
• Power (watts): 20W
• Mounting Type: Surface Mount
• Voltage - Input: 2.95 ~ 5.5 V
• Package / Case: TO-PMOD-7, Power Module
• 1st Output: 0.8 ~ 5 VDC @ 4A
• Size / Dimension: 0.40" L x 0.54" W x 0.18" H (10.16mm x 13.77mm x 4.57mm)
• Power (watts) - Rated: 20W
• Operating Temperature: -40°C ~ 125°C
• Efficiency: 96%
• Approvals: EN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• 3rd Output: -
• 2nd Output: -
• Other names: LMZ10504TZ-ADJTR

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ADDITIONAL FEATURES
Enable
The LMZ10504 features an enable (EN) pin and associated
comparator to allow the user to easily sequence the
LMZ10504 from an external voltage rail, or to manually set
the input UVLO threshold. The turn-on or rising threshold and
hysteresis for this comparator are typically 1.23V and 0.15V
respectively. The precise reference for the enable comparator
allows the user to guarantee that the LMZ10504 will be dis-
abled when the system demands it to be.
The EN pin should not be left floating. For always-on opera-
tion, connect EN to VIN.
Enable AND UVLO
Using a resistor divider from VIN to EN as shown in the
schematic diagram below, the input voltage at which the part
begins switching can be increased above the normal input
UVLO level according to
For example, suppose that the required input UVLO level is
3.69V. Choosing R
kΩ.
Alternatively, the EN pin can be driven from another voltage
source to cater to system sequencing requirements common-
ly found in FPGA and other multi-rail applications. The fol-
lowing schematic shows an LMZ10504 that is sequenced to
start based on the voltage level of a master system rail
(V
Soft-Start
The LMZ10504 begins to operate when both the VIN and EN,
voltages exceed the rising UVLO and enable thresholds, re-
spectively. A controlled soft-start eliminates inrush currents
during startup and allows the user more control and flexibility
when sequencing the LMZ10504 with other power supplies.
OUT1
).
enb
= 10 kΩ, then we calculate R
30088244
ent
30088245
= 20
12
In the event of either VIN or EN decreasing below the falling
UVLO or enable threshold respectively, the voltage on the
soft-start pin is collapsed by discharging the soft-start capac-
itor by a 14 µA (typ.) current sink to ground.
Soft-Start Capacitor
Determine the soft-start capacitance with the following rela-
tionship
where V
I
C
Thus, the required soft-start capacitor per unit output voltage
startup time is given by
For example, a 4 ms soft-start time will yield a 10 nF capaci-
tance. The minimum soft-start capacitance is 680 pF.
Tracking
The LMZ10504 can track the output of a master power supply
during soft-start by connecting a resistor divider to the SS pin.
In this way, the output voltage slew rate of the LMZ10504 will
be controlled by a master supply for loads that require precise
sequencing. When the tracking function is used, a small value
soft-start capacitor should be connected to the SS pin to al-
leviate output voltage overshoot when recovering from a cur-
rent limit fault.
Tracking - Equal Soft-Start Time
One way to use the tracking feature is to design the tracking
resistor divider so that the master supply output voltage,
V
gether and reach their target values at the same time. This is
termed ratiometric startup. For this case, the equation gov-
erning the values of tracking divider resistors R
given by
The above equation includes an offset voltage, of 200 mV, to
ensure that the final value of the SS pin voltage exceeds the
reference voltage of the LMZ10504. This offset will cause the
LMZ10504 output voltage to reach regulation slightly before
the master supply. A value of 33 kΩ 1% is recommended for
R
SS
OUT1
SS
trkt
is the soft-start charging current (nominally 2 µA) and
is the external soft-start capacitance.
as a compromise between high precision and low quies-
, and the LMZ10504 output voltage, V
FB
is the internal reference voltage (nominally 0.8V),
C
SS
= 2.5 nF / ms
OUT2
trkb
, both rise to-
and R
30088257
trkt
is