LM2830XMF/NOPB National Semiconductor, LM2830XMF/NOPB Datasheet - Page 10

• Manufacturer Part Number: LM2830XMF/NOPB
• Description: IC REGULATOR BUCK 1A SOT23-5
• Manufacturer: National Semiconductor
• Type: Step-Down (Buck)r

Specifications of LM2830XMF/NOPB

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.6 ~ 4.5 V
• Current - Output: 1A
• Frequency - Switching: 1.6MHz
• Voltage - Input: 3 ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: SOT-23-5, SC-74A, SOT-25
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: LM2830XMF; LM2830XMFTR

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Applications Information
THEORY OF OPERATION
The LM2830 is a constant frequency PWM buck regulator IC
that delivers a 1.0A load current. The regulator has a preset
switching frequency of 1.6MHz or 3.0MHz. This high frequen-
cy allows the LM2830 to operate with small surface mount
capacitors and inductors, resulting in a DC/DC converter that
requires a minimum amount of board space. The LM2830 is
internally compensated, so it is simple to use and requires few
external components. The LM2830 uses current-mode con-
trol to regulate the output voltage. The following operating
description of the LM2830 will refer to the Simplified Block
Diagram (Figure 1) and to the waveforms in Figure 2. The
LM2830 supplies a regulated output voltage by switching the
internal PMOS control switch at constant frequency and vari-
able duty cycle. A switching cycle begins at the falling edge
of the reset pulse generated by the internal oscillator. When
this pulse goes low, the output control logic turns on the in-
ternal PMOS control switch. During this on-time, the SW pin
voltage (V
tor current (I
by the current sense amplifier, which generates an output
proportional to the switch current. The sense signal is
summed with the regulator’s corrective ramp and compared
to the error amplifier’s output, which is proportional to the dif-
ference between the feedback voltage and V
PWM comparator output goes high, the output switch turns
off until the next switching cycle begins. During the switch off-
time, inductor current discharges through the Schottky catch
diode, which forces the SW pin to swing below ground by the
forward voltage (V
lator loop adjusts the duty cycle (D) to maintain a constant
output voltage.
SW
L
) swings up to approximately V
) increases with a linear slope. I
FIGURE 2. Typical Waveforms
D
) of the Schottky catch diode. The regu-
IN
, and the induc-
REF
L
is measured
. When the
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SOFT-START
This function forces V
ing start up. During soft-start, the error amplifier’s reference
voltage ramps from 0V to its nominal value of 0.6V in approx-
imately 600 µs. This forces the regulator output to ramp up in
a controlled fashion, which helps reduce inrush current.
OUTPUT OVERVOLTAGE PROTECTION
The over-voltage comparator compares the FB pin voltage to
a voltage that is 15% higher than the internal reference
V
reference, the internal PMOS control switch is turned off,
which allows the output voltage to decrease toward regula-
tion.
UNDERVOLTAGE LOCKOUT
Under-voltage lockout (UVLO) prevents the LM2830 from op-
erating until the input voltage exceeds 2.73V (typ). The UVLO
threshold has approximately 430 mV of hysteresis, so the part
will operate until V
vents the part from turning off during power up if V
monotonic.
CURRENT LIMIT
The LM2830 uses cycle-by-cycle current limiting to protect
the output switch. During each switching cycle, a current limit
comparator detects if the output switch current exceeds 1.75A
(typ), and turns off the switch until the next switching cycle
begins.
THERMAL SHUTDOWN
Thermal shutdown limits total power dissipation by turning off
the output switch when the IC junction temperature exceeds
165°C. After thermal shutdown occurs, the output switch
doesn’t turn on until the junction temperature drops to ap-
proximately 150°C.
REF
. Once the FB pin voltage goes 15% above the internal
IN
drops below 2.3V (typ). Hysteresis pre-
OUT
to increase at a controlled rate dur-
IN
is non-