LM3100MH/NOPB National Semiconductor, LM3100MH/NOPB Datasheet - Page 12

• Manufacturer Part Number: LM3100MH/NOPB
• Description: IC REG SIMPLE SW 1.5A 20-TSSOP
• Manufacturer: National Semiconductor
• Series: PowerWise®, SIMPLE SWITCHER®r
• Type: Step-Down (Buck)r

Specifications of LM3100MH/NOPB

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 7 V
• Current - Output: 1.5A
• Frequency - Switching: 1MHz
• Voltage - Input: 4.5 ~ 36 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 20-TSSOP Exposed Pad, 20-eTSSOP, 20-HTSSOP
• Dc To Dc Converter Type: Step Down
• Pin Count: 20
• Input Voltage: 36V
• Output Voltage: 0.8 to 7V
• Switching Freq: 1000KHz
• Output Current: 1.5A
• Efficiency: 86%
• Package Type: TSSOP EP
• Output Type: Adjustable
• Switching Regulator: Yes
• Mounting: Surface Mount
• Input Voltage (min): 4.5V
• Operating Temp Range: -40C to 125C
• Operating Temperature Classification: Automotive
• For Use With: LM3100EVAL - BOARD EVAL LM3100
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Lead Free Status / Rohs Status: Compliant
• Other names: *LM3100MH; *LM3100MH/NOPB; LM3100MH

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nal pull-up resistor. For all cases, this voltage must be limited
not to exceed 7V.
FIGURE 1. Shutdown Implementation
FIGURE 2. Inductor Current - Current Limit Operation
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Current Limit
Current limit detection occurs during the off-time by monitor-
ing the re-circulating current through the low-side syn-
chronous switch. Referring to Functional Block Diagram,
when the buck switch is turned off, inductor current flows
through the load, into PGND, and through the internal low-
side synchronous switch. If that current exceeds 1.9A the
current limit comparator toggles, forcing a delay to the start of
the next on-time period. The next cycle starts when the re-
circulating current falls back below 1.9A and the voltage at FB
is below 0.8V. The inductor current is monitored during the
low-side switch on-time. As long as the overload condition
persists and the inductor current exceeds 1.9A, the high-side
switch will remain inhibited. The operating frequency is lower
during an over-current due to longer than normal off-times.
Figure 2
inductor current is equal to the output current, I
state. When an overload occurs, the inductor current will in-
crease until it exceeds the current limit threshold, 1.9A. Then
the control keeps the high-side switch off until the inductor
current ramps down below 1.9A. Within each on-time period,
the current ramps up an amount equal to:
During this time the LM3100 is in a constant current mode,
with an average load current (I
illustrates an inductor current waveform, the average
OCL
) equal to 1.9A +ΔI/2.
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OUT
in steady
(6)