LDS8620002-T2 Leadis Technology, LDS8620002-T2 Datasheet - Page 7

• Manufacturer Part Number: LDS8620002-T2
• Description: LED Drivers 200mA Dual Output w/ 1-wire intereface
• Manufacturer: Leadis Technology

Specifications of LDS8620002-T2

• Number Of Segments: 2
• Low Level Output Current: 0 mA
• High Level Output Current: 192 mA
• Operating Supply Voltage: 2.7 V to 5.5 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: TQFN EP
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LDS8620
BLOCK DIAGRAM
BASIC OPERATION
At power-up, EN/SET pin should be logic LOW. The
LDS8620 starts operating in 1x mode when EN/SET
pin is asserted logic high and at least one channel is
enabled. At 1x mode, the output will be approximately
equal to the input supply voltage (less any internal
voltage losses). If the output voltage is sufficient to
regulate all LED currents, the device remains in 1x
operating mode.
The low dropout PowerLite™ Current regulator
(PCR) performs well at input voltages up to 50 mV
above LED forward voltage significantly increasing
driver’s efficiency. The LDS8620 monitors voltage
drop Vd across PCR at every channel in ON state. If
this voltage falls below 50 mV (typical) at any one
channel, (channel with LED with highest forward
voltage), the Mode Control Block changes charge
pump mode to the next multiplication ratio.
Vd = V
Charge Pump Output Resistance at given mode, Iout
is sum of all LED currents, and M is a charge pump’
multiplication ratio.
If the input voltage is insufficient or falls to a level
where Vd ≤50 mV, and the regulated currents cannot
be maintained, the low dropout PowerLite™ Current
© 2008 Leadis Technology
Characteristics subject to change without notice
IN
x M – V
F
– Rcp x Iout, where Rcp is a
LEADIS TECHNOLOGY CONFIDENTIAL
Figure 2. LDS8620 Functional Block Diagram
PRELIMINARY
7
Regulator switches the charge pump into 1.33x mode
(after a fixed delay time of about 800 μ s). In 1.33x
mode,
approximately equal to 1.33 times the input supply
voltage (less any internal voltage losses).
This sequence repeats at every mode until driver
enters the 2x mode.
If the device detects a sufficient input voltage is
present to drive all LED currents in 1x mode, it will
change automatically back to 1x mode. This only
applies for changing back to the 1x mode. The
difference between the input voltage when exiting 1x
mode and returning to 1x mode is called the 1x mode
transition hysteresis (about 600 mV).
LED Current Setting
The current in each of the LED is programmed
through the 1-wire EN/SET digital control input. By
pulsing this signal according to a LEADIS 1-wire
protocol, a set of internal registers can be addressed
and written into allowing to configure each of LEDs
with the desired current. There are five registers: the
first is 2 bits long, while registers 2 – 4 are six bits
long, and the fifth is one bit long. The registers are
the
charge
pump’
Doc. No. 8620DS, Rev. 0.4
output
voltage
is