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LM21215AMHE-1 Datasheet(PDF) 18 Page - Texas Instruments

Part No. LM21215AMHE-1
Description  15-A Ultra High-Efficiency Synchronous Buck Converter
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Maker  TI1 [Texas Instruments]
Homepage  http://www.ti.com
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LM21215AMHE-1 Datasheet(HTML) 18 Page - Texas Instruments

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EN
AVIN
REN1
LM21215A-1
Input Power
Supply
REN2
FB1
OUT
FB2
R
V
0.6V
1
R
§
·
˜ ¨
¸
©
¹
RFB1
RFB2
FB
VOUT
LM21215A-1
0.6V
LM21215A
SNOSB87C – MARCH 2011 – REVISED JANUARY 2016
www.ti.com
Table 1. Design Parameters
DESIGN PARAMETER
EXAMPLE VALUE
VIN
5 V
VOUT
1.2 V
IOUT
15 A
FSW
500 kHz
fcrossover
100 kHz
ΔVOUT(pk-pk)
10 mV
8.2.1.2 Detailed Design Procedure
8.2.1.2.1
Output Voltage Setpoint
The first step in designing an LM21215A application is to configure the output voltage setpoint by using a voltage
divider between VOUT and AGND, with the middle node connected to FB. When operating under steady state
conditions, the LM21215A regulates VOUT such that the FB voltage is driven to 0.6 V.
Figure 29. Setting the Output Voltage by Feedback Resistor Divider
A good starting point for the lower feedback resistor, RFB2, is 10 kΩ. Calculate RFB1 using Equation 3.
(3)
8.2.1.2.2
Precision Enable
The Enable (EN) pin of the LM21215A allows the output to be toggled on and off. This pin is a precision analog
input. When the voltage exceeds 1.35 V, the converter begins to regulate the output voltage as long as AVIN has
exceeded the UVLO threshold voltage of 2.7 V. There is an internal pullup current source of 2 µA connected to
EN. If enable is not used, the device turns on automatically. Also, if EN is not toggled directly, the device can be
set to turn on at a certain input voltage higher than the internal UVLO rising threshold. This is achieved with an
external resistor divider from AVIN to EN and EN to AGND as shown in Figure 30.
Figure 30. Input Voltage Turn-on Setpoint Configured by Enable Resistor Divider
The resistances of REN1 and REN2 are chosen to allow EN to reach its rising threshold voltage at the desired the
input supply voltage. With the enable current source included, use Equation 4 to solve for REN1.
18
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Product Folder Links: LM21215A


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