LM5022LEDEVAL National Semiconductor, LM5022LEDEVAL Datasheet - Page 3

• Manufacturer Part Number: LM5022LEDEVAL
• Description: BOARD EVALUATION FOR LM5022
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM5022LEDEVAL

• Current - Output / Channel: 1A
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 40V
• Features: Dimmable
• Voltage - Input: 10 ~ 14V
• Utilized Ic / Part: LM5022
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Testing The Converter
Figure 5 shows a block diagram of connections for making
measurements of efficiency. The wires used for making con-
nections at the input should be rated to at least 5A of contin-
uous current and should be no longer than is needed for
convenient testing. A series ammeter capable of measuring
10A or more should be used for both the input and the output
lines. Dedicated voltmeters should be connected with their
positive and negative leads right at the four power terminals
Permanent Components
The following components should remain the same for any
new circuits tested on the LM5022 boost LED evaluation
board:
Name
Cinx
Rpd
Rs1
Ccs
Cf
FIGURE 5. Efficiency Measurement Setup
0.1 µF
Value
10 kΩ
100Ω
1 µF
1 nF
3
at the sides of the board. This measurement technique mini-
mizes the resistive loss in the wires that connect the evalua-
tion board to the input power supply and the LEDs. Output
ripple current measurements should be taken with an oscil-
loscope and an AC current probe or AC-coupled DC current
probe. This measurement can be taken anywhere in the loop
formed by the LEDs and J1, however the recommended lo-
cation is between the LED+/J1 connector and the anode of
the first LED.
Additional Footprints
The 100 pF capacitor Csyc provides an AC input path for ex-
ternal clock synchronization. Detection of the sync pulse re-
quires a peak voltage level greater than 3.7V at the RT/SYNC
pin. Note the DC voltage at RT/SYNC is approximately 2V to
allow compatibility with 3.3V logic. The sync pulse width
should be set between 15 ns to 150 ns by the external com-
ponents. The Rt resistor is always required, whether the
oscillator is free running or externally synchronized. Rt must
be selected so that the free-running oscillator frequency is
below the lowest synchronization frequency.
Footprint U2 and current limiting resistor Rz allow the user to
add a shunt regulator voltage reference or zener diode to
maintain tight control over the bias current through the right-
hand transistor of Q2 as the output voltage changes. Tight
regulation of the bias current allows better accuracy of the
LED current. When using this method resistor Rb is re-se-
lected to draw the 1 mA bias current using the following
equation:
Rb = (V
The 0Ω placeholder Rz is re-selected to bias the zener/refer-
ence voltage and Q2 using the following:
Rz = (V
O-MIN
Z
– 0.6) / 0.001 (V
- V
Z
) / (I
Z
+ 0.001) (I
Z
current)
is the zener or reference voltage)
Z
is the zener/reference bias
www.national.com
30013305