Quick Start Procedure - Linear Technology DC2257A Demo Manual

DEMO MANUAL DC2257A
PERFORMANCE SUMMARY
PARAMETER
Minimum Input Voltage, V
PVIN
Maximum Input Voltage – Switching, V
Maximum Input Voltage – Not Switching, V
Maximum LED Voltage, V
LED
LED Current, I
LED
Input Turn-On Voltage, V
PVIN(EN)
Input Turn-Off Voltage, V
PVIN(UVLO)
Input OVLO Turn-Off Voltage, V
PVIN(OVLO_TURN-OFF)
Input OVLO Turn-On Voltage, V
PVIN(OVLO_TURN-ON
Efficiency
Switching Frequency
Input Current Limit

QUICK START PROCEDURE

To use DC2257A to evaluate the performance of the
LTM8005, refer to Figure 1 for the proper measurement
equipment setup and then follow the procedure below.
NOTE: PWM must be pulled high to work. If PWM is not
used, connect the PWM terminal to a 2V to 5V source or
connect the PWM pin to V
1. Connect a string of LEDs with a forward voltage of 35V
or less, but greater than the PVIN voltage, to the LED
and GND terminals on the PCB as shown in Figure 1.
2. Connect the EN/UVLO terminal to ground with a
clip-on lead.
3. With the power off, connect the input power supply to
the PVIN and GND terminals within the voltage range
specified on the PCB. Make sure that the input power
2
Specifications are at T
CONDITIONS
PVIN
V ≥ 1.25
PVIN OVLO
R5 = 100k, R6 = 73.2k
R7 = 19.1k, R8 = 1M, R9 = 93.1k, V
R7 = 19.1k, R8 =1M, R9 = 93.1k, V
R7 = 19.1k, R8 = 1M, R9 = 93.1k, V
) R7 = 19.1k, R8 = 1M, R9 = 93.1k, V
V = 12V, V
PVIN
R1 = 23.2k, Spread Spectrum = OFF
RS1 = 0.008Ω
on the PCB using R18.
REF
= 25°C
A
Rising
PVIN
Falling
PVIN
Rising
PVIN
Falling
PVIN
= 35V, I = 1.2A
LED LED
supply voltage does not exceed the forward voltage of
the LED string. OVLO becomes active to inhibit switch-
ing for an input voltage of greater than 29V.
4. Connect an input to the PWM terminal. If PWM is not
used, connect PWM to a 2V to 5V DC source or to V
on the PCB using resistor R18. PWM must be pulled
high to work. For PWM dimming, connect a 100Hz or
higher PWM signal to the PWM terminal.
+
5. Turn the PVIN power supply on.
6. Release the EN/UVLO to GND connection.
7. Observe the LED string running at the programmed
LED current; or, observe the reduction of brightness
in the LED string with PWM dimming.
MIN TYP MAX
6V
27V
38V
35V
1.2A
5.9V
4.9V
29.1V
28.4V
92%
350kHz
7.5A Peak
REF
dc2257af