SP7685ER-L Exar Corporation, SP7685ER-L Datasheet - Page 4

• Manufacturer Part Number: SP7685ER-L
• Description: LED Drivers 1.2A Bck/Bst Charge Pump LED Driver
• Manufacturer: Exar Corporation
• Series: -r

Specifications of SP7685ER-L

• Low Level Output Current: 0.4 A
• High Level Output Current: 2 A
• Operating Supply Voltage: 2.7 V to 5.5 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: DFN-10
• Minimum Operating Temperature: - 40 C
• Constant Current: -
• Constant Voltage: -
• Topology: PWM, Step-Down (Buck), Step-Up (Boost), Switched Capacitor (Charge Pump)
• Number Of Outputs: 1
• Internal Driver: Yes
• Type - Primary: Backlight, Flash/Torch
• Type - Secondary: High Brightness LED (HBLED), White LED
• Frequency: 2.4MHz
• Voltage - Supply: 2.7 V ~ 5.5 V
• Voltage - Output: -
• Mounting Type: Surface Mount
• Operating Temperature: -40°C ~ 85°C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The SP7685 is a charge pump regulator
designed for converting a Li-Ion battery
voltage of 2.7V to 4.2V to drive a white LED
used in digital still camera Flash and Torch
applications. The SP7685 has two modes
of operation which are pin-selectable for
either Flash or Torch. Flash mode is usually
used with a pulse of about 200 to 300
milliseconds to generate a high intensity
Flash. Torch can be used continuously at a
lower output current than Flash and is often
used for several seconds in a digital still
camera “movie” mode.
The SP7685 also has two modes of opera-
tion to control the output current: the 1X
mode and 2X mode. Operation begins after
the enable pin EN receives a logic high, the
bandgap reference wakes up after 200μs,
and then SP7685 goes through a soft-start
mode designed to reduce inrush current.
The SP7685 starts in the 1X mode, which
Date: 6/20/06 Rev T
RSET
6
RSET
R
SET
REF=
RSET BLOCK
{
R
5
SET
}
x 14μA
+
-
+
-
BG REF
1.26V
FLASH
SP7685, 1.2A Buck/BoostCharge Pump LED Driver
RSET REF
RESISTOR
FLASH=1, S=1, RSET REF
FLASH=0, S=0, 50mV
TAPS
4
50mV
145C OFF
135C ON
0 s
1
MUX
2x1
2.4MH
CLK
4
FB REF
SGND 8
FB
Z
OVER TEMP COMP
THERMAL FAULT
7
acts like a linear regulator to control the
output current by continuously monitoring
the feedback pin FB. In 1X mode, if the
SP7685 auto detects a dropout condition,
which is when the FB pin is below the
regulation point for more than 32 cycles of
the internal clock, the SP7685 automati-
cally switches to the 2X mode. The SP7685
remains in the 2X mode until one of four
things happens: 1) the enable pin EN has
been toggled, 2) the Flash pin has changed
from high to low, 3) V
thermal fault occurs.
The 2X mode is the charge pump mode
where the output can be pumped as high as
two times the input voltage, provided the
output does not exceed the maximum volt-
age for the SP7685, which is internally
limited to about 5.5V. In the 2X mode, as in
the 1X mode, the output current is regulated
by the voltage at the FB pin.
CLK
-
+
FB
COM P
VIN
EN
5
ONE
SHOT
FB COMP
1
SWITCHES
CHARGE
PUMP
THEORY OF OPERATION
FUNCTIONAL DIAGRAM
CLK
MODE SWITCH
0 =1X
1=2X
CLR
COUNTER
32 COUNT
IN
is cycled or, 4) a
PGND
© 2006 Sipex Corporation
VOUT
C2
C1
SET
DOMINANT
R
S
0