LM2733YEVAL National Semiconductor, LM2733YEVAL Datasheet - Page 12

• Manufacturer Part Number: LM2733YEVAL
• Description: BOARD EVALUATION LM2733Y
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM2733YEVAL

• Main Purpose: DC/DC, Step Up
• Outputs And Type: 1, Non-Isolated
• Current - Output: 1A
• Voltage - Input: 2.7 ~ 14V
• Regulator Topology: Boost
• Frequency - Switching: 600kHz
• Board Type: Fully Populated
• Utilized Ic / Part: LM2733
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Voltage - Output: -
• Power - Output: -

www.national.com
There will be some switching losses as well, so some derating
needs to be applied when calculating IC power dissipation.
MINIMUM INDUCTANCE
In some applications where the maximum load current is rel-
atively small, it may be advantageous to use the smallest
possible inductance value for cost and size savings. The con-
verter will operate in discontinuous mode in such a case.
The minimum inductance should be selected such that the
inductor (switch) current peak on each cycle does not reach
the 1A current limit maximum. To understand how to do this,
an example will be presented.
In the example, the LM2733X will be used (nominal switching
frequency
1.15 MHz). This means the maximum cycle period is the re-
ciprocal of the minimum frequency:
We will assume the input voltage is 5V, V
0.2V, V
Duty Cycle = 60.3%
Therefore, the maximum switch ON time is 0.524 µs. An in-
ductor should be selected with enough inductance to prevent
the switch current from reaching 1A in the 0.524 µs ON time
interval (see below):
Discontinuous Design, 5V–12V Boost (LM2733X)
DIODE
1.6
= 0.3V. The duty cycle is:
T
ON(max)
MHz,
= 1/1.15M = 0.870 µs
minimum
switching
OUT
= 12V, V
frequency
20055413
SW
=
12
The voltage across the inductor during ON time is 4.8V. Min-
imum inductance value is found by:
In this case, a 2.7 µH inductor could be used assuming it pro-
vided at least that much inductance up to the 1A current value.
This same analysis can be used to find the minimum induc-
tance for any boost application. Using the slower switching
“Y” version requires a higher amount of minimum inductance
because of the longer switching period.
INDUCTOR SUPPLIERS
Some of the recommended suppliers of inductors for this
product include, but not limited to are Sumida, Coilcraft, Pana-
sonic, TDK and Murata. When selecting an inductor, make
certain that the continuous current rating is high enough to
avoid saturation at peak currents. A suitable core type must
be used to minimize core (switching) losses, and wire power
losses must be considered when selecting the current rating.
SHUTDOWN PIN OPERATION
The device is turned off by pulling the shutdown pin low. If this
function is not going to be used, the pin should be tied directly
to V
must be used to V
ed). The SHDN pin must not be left unterminated.
V = L X dl/dt, L = V X (dt/dl) = 4.8 (0.524µ/1) = 2.5 µH
IN
. If the SHDN function will be needed, a pull-up resistor
IN
(approximately 50k-100kΩ recommend-