LM2574MX-ADJ/NOPB National Semiconductor, LM2574MX-ADJ/NOPB Datasheet - Page 21

• Manufacturer Part Number: LM2574MX-ADJ/NOPB
• Description: IC REG SIMPLE SWITCHER 14-SOIC
• Manufacturer: National Semiconductor
• Series: SIMPLE SWITCHER®r
• Type: Step-Down (Buck)r

Specifications of LM2574MX-ADJ/NOPB

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.23 ~ 37 V
• Current - Output: 500mA
• Frequency - Switching: 52kHz
• Voltage - Input: 4 ~ 40 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 14-SOIC (7.5mm Width)
• Power - Output: 750mW
• Dc To Dc Converter Type: Inverting/Step Down
• Pin Count: 14
• Input Voltage: 40V
• Output Voltage: 1.23 to 37V
• Switching Freq: 47 TO 58KHz
• Output Current: 500mA
• Efficiency: 77%
• Package Type: SOIC W
• Output Type: Adjustable
• Switching Regulator: Yes
• Mounting: Surface Mount
• Input Voltage (min): 4V
• Operating Temp Range: -40C to 125C
• Operating Temperature Classification: Automotive
• Leaded Process Compatible: Yes
• Rohs Compliant: Yes
• Peak Reflow Compatible (260 C): Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *LM2574MX-ADJ; *LM2574MX-ADJ/NOPB; LM2574MX-ADJ; LM2574MX-ADJTR

Additional Applications
Note: Pin numbers are for 8-pin DIP package.
Definition of Terms
BUCK REGULATOR
A switching regulator topology in which a higher voltage is
converted to a lower voltage. Also known as a step-down
switching regulator.
BUCK-BOOST REGULATOR
A switching regulator topology in which a positive voltage is
converted to a negative voltage without a transformer.
DUTY CYCLE (D)
Ratio of the output switch’s on-time to the oscillator period.
CATCH DIODE OR CURRENT STEERING DIODE
The diode which provides a return path for the load current
when the LM2574 switch is OFF.
EFFICIENCY ( )
The proportion of input power actually delivered to the load.
CAPACITOR EQUIVALENT SERIES RESISTANCE (ESR)
The purely resistive component of a real capacitor’s imped-
ance (see Figure 17 ). It causes power loss resulting in ca-
pacitor heating, which directly affects the capacitor’s operat-
ing lifetime. When used as a switching regulator output filter,
higher ESR values result in higher output ripple voltages.
Most standard aluminum electrolytic capacitors in the
100 µF–1000 µF range have 0.5
FIGURE 17. Simple Model of a Real Capacitor
FIGURE 16. 1.2V to 55V Adjustable 500 mA Power Supply with Low Output Ripple
DS011394-25
to 0.1
(Continued)
ESR. Higher-
21
grade capacitors (“low-ESR”, “high-frequency”, or “low-
inductance”) in the 100 µF–1000 µF range generally have
ESR of less than 0.15 .
EQUIVALENT SERIES INDUCTANCE (ESL)
The pure inductance component of a capacitor (see Figure
17 ). The amount of inductance is determined to a large ex-
tent on the capacitor’s construction. In a buck regulator, this
unwanted inductance causes voltage spikes to appear on
the output.
OUTPUT RIPPLE VOLTAGE
The AC component of the switching regulator’s output volt-
age. It is usually dominated by the output capacitor’s ESR
multiplied by the inductor’s ripple current ( I
to-peak value of this sawtooth ripple current can be deter-
mined by reading the Inductor Ripple Current section of the
Application hints.
CAPACITOR RIPPLE CURRENT
RMS value of the maximum allowable alternating current at
which a capacitor can be operated continuously at a speci-
fied temperature.
STANDBY QUIESCENT CURRENT (I
Supply current required by the LM2574 when in the standby
mode (ON/OFF pin is driven to TTL-high voltage, thus turn-
ing the output switch OFF).
INDUCTOR RIPPLE CURRENT ( I
The peak-to-peak value of the inductor current waveform,
typically a sawtooth waveform when the regulator is operat-
ing in the continuous mode (vs. discontinuous mode).
CONTINUOUS/DISCONTINUOUS MODE OPERATION
Relates to the inductor current. In the continuous mode, the
inductor current is always flowing and never drops to zero,
vs. the discontinuous mode, where the inductor current
drops to zero for a period of time in the normal switching
cycle.
IND
STBY
)
)
IND
). The peak-
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DS011394-24