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SP7683 Fiches technique(PDF) 5 Page - Sipex Corporation

No de pièce SP7683
Description  Four Channel Charge Pump Regulator LED Driver
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Fabricant  SIPEX [Sipex Corporation]
Site Internet  http://www.sipex.com
Logo SIPEX - Sipex Corporation

SP7683 Fiches technique(HTML) 5 Page - Sipex Corporation

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Date: 12/21/04
SP7683 Four Channel Charge Pump LED Driver
© Copyright 2004 Sipex Corporation
The SP7683 is comprised of two stages. First is a regulated change pump to convert the input
voltage V
IN into a stable output voltage or current depending on the mode used. The second stage
is a low dropout current matching regulator that provides stable identical currents in all four
channels to drive LED1 - LED4. The first stage can drive an additional four LEDs that are
connected in parallel to the V
OUT pin. It is recommended to use resistors in series with these
additional diodes for current matching.
The SP7683 provides dimming control for the LEDs, with a constant ratio of brightness between
them. It can also be used to turn off the LEDs completely.
The Charge Pump
The regulated charge pump can operate in two modes 1X V
IN and 1.5X VIN to optimize efficiency
over the entire battery voltage range. The input voltage trip point at which the charge pump will
automatically switch from a 1X mode to 1.5X mode is defined by an external voltage divider
connected to V
MODE pin. Cycle-by-cycle regulation ensures that no mode change occurs during
a switching cycle. To achieve better efficiency it is recommended that the V
IN_TRIP is set at
V
IN_TRIP = VF + 0.31 + MILED *ROUT where VF is the LED forward voltage and (M) is the number of LEDs
connected to V
OUT . ROUT is the output resistance. ILED is the current per LED.
The charge pump may be configured in voltage mode or as a current source. When used as a
voltage source the output voltage is determined by an external resistive divider connected to FB
pin as: V
OUT = (1+R10/R5)*VFB (see Figure 2) where VFB = 0.31V.
When used as a current source the current in one single LED (D5 - D8) may be set by series
resistor R
S as ILED = VFB / RS. The current in the remaining LEDs will track based on the ballast
resistors. Three-wire LED modules with internal series resistors can also be driven in this way.
The flying capacitors C1 an C2 of the charge pump control the tade-off between the output voltage
ripple and the output current capability. Decreasing the flying capacitors will reduce the output
voltage ripple because less charge will be delivered to the output capacitor. However, smaller
flying capacitors lead to larger output resistance, thus decreasing the output current handling
capability and circuit efficiency. We recommend using ceramic capacitors in the range of 1µF -
4.7µF with low ESR, which helps reduce peak-to-peak output ripple and reduce high frequency
noise spikes.
Dimming control can be achieved by applying a PWM control signal to the EN/PWM pin. The
brightness of the LEDs is controlled by varying the duty cycle of the PWM signal. PWM repetition
rate from 60Hz - 700Hz. A repetition rate of at least 60Hz is required to prevent visible flickering.
Applying a logic low signal to EN/PWM control input turns of the device resulting in supply current
below 1µA and high impedance state of the V
OUT pin.
CIRCUIT DESCRIPTION


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