LM2854MH-1000/NOPB National Semiconductor, LM2854MH-1000/NOPB Datasheet - Page 11

• Manufacturer Part Number: LM2854MH-1000/NOPB
• Description: IC REG 4A SYNC SMPL SW 16ETSSOP
• Manufacturer: National Semiconductor
• Series: PowerWise®, SIMPLE SWITCHER®r
• Type: Step-Down (Buck)r

Specifications of LM2854MH-1000/NOPB

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 5 V
• Current - Output: 4A
• Frequency - Switching: 1MHz
• Voltage - Input: 2.95 ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP Exposed Pad, 16-eTSSOP, 16-HTSSOP
• Primary Input Voltage: 5.5V
• No. Of Outputs: 1
• Output Voltage: 5V
• Output Current: 4A
• Voltage Regulator Case Style: TSSOP
• No. Of Pins: 16
• Operating Temperature Range: -40°C To +125°C
• Svhc: No SVHC (15-Dec-2010)
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: *LM2854MH-1000; *LM2854MH-1000/NOPB; LM2854MH-1000

Block Diagram
Applications Information
GENERAL
The LM2854 PowerWise® synchronous DC-DC buck regu-
lator belongs to the National Semiconductor SIMPLE
SWITCHER® family of switching regulators. Integration of the
power MOSFETs and associated drivers, compensation com-
ponent network and the PWM controller reduces the number
of external components necessary for a complete power sup-
ply design, without sacrificing performance.
Operation Description
SWITCHING FREQUENCY
The LM2854 is available in two switching frequency options,
500 kHz and 1 MHz. Generally, a higher switching frequency
allows for faster transient response and a reduction in the
footprint area and volume of the external power stage com-
ponents, while a lower switching frequency affords better
efficiency. These factors should be considered when select-
ing the appropriate switching frequency for a given applica-
tion.
ENABLE
The LM2854 features a enable (EN) pin and associated com-
parator to allow the user to easily sequence the LM2854 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 LM2854 will be disabled when the
system demands it to be.
SOFT-START
The LM2854 begins to operate when both the AVIN and EN
voltages exceed the rising UVLO and enable thresholds, re-
11
spectively. A controlled soft-start eliminates inrush currents
during start-up and allows the user more control and flexibility
when sequencing the LM2854 with other power supplies. An
external soft-start capacitor is used to control the LM2854
start-up time. During soft-start, the voltage on the feedback
pin is connected internally to the non-inverting input of the
error amplifier. The soft-start period lasts until the voltage on
the soft-start pin exceeds the LM2854 reference voltage of
0.8V. At this point, the reference voltage takes over at the non-
inverting amplifier input.
In the event of either AVIN 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 through a 5 kΩ transistor to ground.
TRACKING
The LM2854 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 LM2854 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 can be connected to the SS pin to alleviate
output voltage overshoot when recovering from a current limit
fault.
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