SP6690EB Datasheet, PDF (2/6 Pages) Sipex Corporation – Evaluation Board Manual

USING THE EVALUATION BOARD
1) Powering Up the SP6690 Circuit
The SP6690 Evaluation Board can be
powered from inputs from a +1.2V to +5.0V.
Connect with short leads directly to the “VIN”
and “GND” posts. Monitor the Output
Voltage and connect the Load between the
“VOUT” post and the “GND” post.
2) Using the J1 Jumper: Enabling the
SP6690 Output and using the Shutdown
Mode
The SP6690 output will be enabled if the J1
Jumper is in the bottom or pin 1 to 2
position. If J1 is in the pin 2 to 3 or top
position, the Shutdown pin is brought to
GND, which puts the SP6690 in the low
quiescent Shutdown Mode.
3) Using the Posts
Since the part might get damaged when the
output is open loop, two divider resistors
(R₁=1M, R₂=64.9K) are used to provide the
feedback loop and set the output voltage.
For the white LEDs application, these two
resistors (R₁, R₂) need to be removed from
the evaluation board first to avoid over-
voltage and then plug the white LED module
between “VOUT” and “FB” posts. The bias
resistor R_b should also be installed on the
board.
4) Inductor Selection
For SP6690, the internal switch will be
turned off only after the inductor current
reaches the typical dc current limit
(I_LIM=350mA). However, there is typically
propagation delay of 200nS between the
time when the current limit is reached and
when the switch is actually turned off. During
this 200nS delay, the peak inductor current
will increase, exceeding the current limit by
a small amount. The peak inductor current
can be estimated by:
I _pk
=
I_LIM
+
V_{in (max)}
L
⋅ 200nS
The larger the input voltage and the lower
the inductor value, the greater the peak
current.
In selecting an inductor, the saturation
current specified for the inductor needs to be
greater than the SP6690 peak current to
avoid saturating the inductor, which would
result in a loss in efficiency and could
damage the inductor.
Choosing an inductor with low DCR
decreases power losses and increase
efficiency.
Refer to Table 1 for some suggested low
ESR inductors.
Table 1. Suggested Low ESR inductor
MANUFACTURE PART NUMBER
MURATA
770-436-1300
LQH32CN100K11
(10uH)
DCR
(Ω)
0.3
Current
Rating
(mA)
450
TDK
847-803-6100
NLC453232T-100K
(22uH)
0.55
500
5) Diode Selection
A schottky diode with a low forward drop
and fast switching speed is ideally used here
to achieve high efficiency. In selecting a
Schottky diode, the current rating of the
schottky diode should be larger than the
peak inductor current. Moreover, the reverse
breakdown voltage of the schottky diode
should be larger than the output voltage.
6) Capacitor Selection
Ceramic capacitors are recommended for
their inherently low ESR, which will help
produce low peak to peak output ripple, and
reduce high frequency spikes.
For the typical application, 4.7uF input
capacitor and 2.2uF output capacitor are
sufficient. The input and output ripple could
be further reduced by increasing the value of
the input and output capacitors. Place all the
capacitors as close to the SP6690 as
possible for layout. For use as a voltage
source, to reduce the output ripple, a small
feedforward (47pF) across the top feedback
resistor can be used to provide sufficient
overdrive for the error comparator, thus
reducing the output ripple.
Refer to Table 2 for some suggested low
ESR capacitors.