LM25011MY/NOPB National Semiconductor, LM25011MY/NOPB Datasheet - Page 12

• Manufacturer Part Number: LM25011MY/NOPB
• Description: IC BUCK ADJ 2A 10MSOP
• Manufacturer: National Semiconductor
• Type: Step-Down (Buck)r

Specifications of LM25011MY/NOPB

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 2.51 ~ 40 V
• Current - Output: 2A
• Frequency - Switching: Up to 2MHz
• Voltage - Input: 6 ~ 42 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP Exposed Pad, 10-HMSOP, 10-eMSOP
• Power - Output: 155mW
• Primary Input Voltage: 42V
• No. Of Outputs: 1
• Output Voltage: 40V
• Output Current: 2A
• No. Of Pins: 10
• Operating Temperature Range: -40°C To +125°C
• Msl: MSL 3 - 168 Hours
• Filter Terminals: SMD
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM25011MYTR

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Ripple Requirements
The LM25011 requires about 25mVp-p of ripple voltage at the
CS pin. Higher switching frequency may require more ripple.
That ripple voltage is generated by the decreasing recirculat-
ing current (the inductor’s ripple current) through R
the off-time. See Figure 3.
The ripple voltage is equal to:
where ΔI is the inductor current ripple amplitude, and R
the current sense resistor at the CS pin.
More ripple can be achieved by decreasing the inductor value.
The LM25011A, with its shorter minimum off-time, typically
will require more ripple than the LM25011. An external circuit
to increase the effective ripple voltage may be needed. Dif-
ferent methods of generating this ripple are explained in the
“Application Information” section.
FIGURE 3. CS Pin Waveform
V
RIPPLE
= ΔI x R
S
FIGURE 2. Normal and Current Limit Operation
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during
S
is
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N-Channel Buck Switch and Driver
The LM25011 integrates an N-Channel buck switch and as-
sociated floating high voltage gate driver. The gate driver
circuit works in conjunction with an external bootstrap capac-
itor (C
pacitor connected between BST and SW provides the supply
voltage for the driver during the on-time. During each off-time,
the SW pin is at approximately -1V, and C
from the internal 5V regulator for the next on-time. The mini-
mum off-time ensures a sufficient time each cycle to recharge
the bootstrap capacitor.
Soft-Start
The soft-start feature allows the converter to gradually reach
a steady state operating point, thereby reducing startup
stresses and current surges. Upon turn-on, when V
its under-voltage lock-out threshold an internal 10 µA current
source charges the external capacitor at the SS pin to 2.51V
(t1 in Figure 1). The ramping voltage at SS ramps the non-
inverting input of the regulation comparator, and the output
voltage, in a controlled manner. For proper operation, the soft-
start capacitor should be no smaller than 1000 pF.
The LM25011 can be employed as a tracking regulator by
applying the controlling voltage to the SS pin. The regulator’s
output voltage tracks the applied voltage, gained up by the
ratio of the feedback resistors. The applied voltage at the SS
pin must be within the range of 0.5V to 2.6V. The absolute
maximum rating for the SS pin is 3.0V. If the tracking function
causes the voltage at the FB pin to go below the thresholds
for the PGD pin, the PGD pin will switch low (see the Power
Good Output section). An internal switch grounds the SS pin
if the input voltage at VIN is below its under-voltage lock-out
threshold or if the Thermal Shutdown activates. If the tracking
function (described above) is used, the tracking voltage ap-
BST
) and an internal high voltage diode. A 0.1 µF ca-
BST
is recharged
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reaches