Datasheet

R1 = 100 k:
C1 = 1.7 pF
C2 = 9 pF
8 30 Ps
3.4V
3.4V
3.4V
EN
VCON
V
OUT
I
LOAD
0V
0A
< 200 mA
8 30 Ps
7 20 Ps
7 20 Ps
7 20 Ps
1V
1.7A
7 20 Ps
VCON = 0.4V
LM3243
www.ti.com SNVS782B –OCTOBER 2010–REVISED FEBRUARY 2013
Figure 22. Dynamic Adjustment of Output Voltage with GPIO
VCON Pin
Figure 23 shows the equivalent CRC circuit for the VCON pin. This circuit is internal to the part and should be
taken into consideration when driving this pin.
Figure 23. VCON Pin Equivalent CRC Circuit
Inductor Selection
A 1.5 µH inductor is needed for optimum performance and functionality of the LM3243. In the case of 2G
transmission current bursts, the effective overall RMS current requirements are reduced. Therefore, please
consult with the inductor manufacturers to determine if some of their smaller components will meet your
application needs even though the classical inductor specification does not appear to meet the LM3243 RMS
current specifications.
LM3243 automatically manages the inductor peak and RMS (or steady current peak) current through the SW pin.
The SW pin has two positive current limits. The first is the 1.45A typical (or 1.65A maximum.) over-limit current
protection. It sets the upper steady-state inductor peak current (as detailed in the Electrical Characteristics Table
- I
LIM,PFET,SteadyState
). It is the dominant factor limiting the inductor's I
SAT
requirement. The second is a over-limit
current protection. It limits the maximum peak inductor current during large signal transients (i.e., < 20 µs) to
1.9A typical (or 2.1A maximum). A minimum inductance of 0.3 µH should be maintained at the second current
limit.
The ACB circuit automatically adjusts its output current to keep the steady-state inductor current below the
steady-state peak current limit. Thus, the inductor RMS current will effectively always be less than the
I
LIM,PFET,SteadyState
during the transmit burst. In addition, as in the case with 2G where the output current comes in
bursts, the effective overall RMS current would be much lower.
For good efficiency, the inductor’s resistance should be less than 0.2Ω; low DCR inductors (<0.2Ω) are
recommended. Table 3 suggests some inductors and suppliers.
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