LM25088MH-1/NOPB National Semiconductor, LM25088MH-1/NOPB Datasheet - Page 14

• Manufacturer Part Number: LM25088MH-1/NOPB
• Description: IC CTLR BUCK NON-SYNC 16-TSSOP
• Manufacturer: National Semiconductor
• Series: PowerWise®r
• Type: Step-Down (Buck)r

Specifications of LM25088MH-1/NOPB

• Design Resources: LM(2)5088-1/2 QS Component Calculator
• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.21 ~ 45 V
• Current - Output: 10A
• Frequency - Switching: 200kHz, 500kHz
• Voltage - Input: 4.5 ~ 42 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP Exposed Pad, 16-eTSSOP, 16-HTSSOP
• Primary Input Voltage: 42V
• No. Of Outputs: 1
• Output Voltage: 1.2V
• Output Current: 10A
• No. Of Pins: 16
• Operating Temperature Range: -40°C To +125°C
• Msl: MSL 1 - Unlimited
• Filter Terminals: SMD
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: LM25088MH-1

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Figure 6 shows the conducted emissions on the LM25088
evaluation board input power line. It can be seen from the
above picture that, the peak emissions with non-dithering op-
eration are centered narrowly at the operating frequency of
the converter. With dithering operation, the conducted emis-
sions are spread around the operating frequency and the
maximum amplitude is reduced by approximately 10dB. (Fig-
ure 6 was captured using a Chroma DC power supply model
number 62006P and an Agilent network analyzer model num-
ber 4395A).
FIGURE 6. Conducted Emissions Measured at the Input
of a LM25088 Based Buck Converter
FIGURE 5. Frequency Dithering Scheme
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Cycle-by-Cycle Current Limit
The LM25088 contains a current limit feature that protects the
circuit from extended over current conditions. The emulated
current signal is directly proportional to the buck switch cur-
rent and is applied to the current limit comparator. If the
emulated current exceeds 1.2V, the PWM cycle is terminated.
The peak inductor current required to trigger the current limit
comparator is given by:
Where, A = 10V/V is the current sense amplifier gain, C
is the Ramp capacitor, R
is the voltage ramp added for slope compensation and 1.2V
is the reference of the current limit comparator.
Since the current that charges the RAMP capacitor is propor-
tional to VIN-VOUT, if the output is suddenly shorted, the
VOUT term is zero and the RAMP charging current increases.
The increased RAMP charging current will immediately re-
duce the PWM duty cycle.The LM25088 also includes a buck
switch protection scheme. A dedicated comparator monitors
S
is the sense resistor,
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RAMP