SP7685ER-L Exar Corporation, SP7685ER-L Datasheet - Page 9

• 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 input and output capacitors should be
located as close to the V
possible to obtain best bypassing, and the
returns should be connected directly to the
P
under the SP7685. The fly capacitor should
be located as close to the C1 and C2 pins as
possible. See typical circuit layout at the end
of this section for details on the recom-
mended layout.
To obtain low output ripple, a value of 10μF
is recommended for C
rents of 500mA to 1.2A, the recommended
C
used. Output currents in Flash of 100mA to
400mA can use a 0.47μF C
4.7μF C
The SP7685 charge pump circuit requires
three capacitors: 10μF input, 10μF output
and 1μF fly capacitor are typically recom-
mended. For the input capacitor, a value of
10μF will help reduce input voltage ripple for
applications sensitive to ripple on the battery
voltage. All the capacitors should be sur-
face mount ceramic for low lead inductance
necessary at the 2.4MHz switching frequency
of the SP7685 and to obtain low ESR, which
improves bypassing on the input and output
and improves output voltage drive by reduc-
ing output resistance. Ceramic capacitors
with X5R or X7R temperature grade are
recommended for most applications. A se-
lection of recommended capacitors is in-
cluded in Table 1 below.
Table 1: Recommended Capacitors
Date: 6/20/06 Rev T
TDK: www.tdk.com
TDK: www.tdk.com
TDK: www.tdk.com
Murata: www.murata.com
Murata: www.murata.com
Murata: www.murata.com
GND
FC
Manufacturer's Website
fly capacitor value of 1μF should be
pin or to the thermal pad ground located
OUT
is still needed.
OUT
IN
. For output cur-
and V
FC
GRM155R60J105KE19B
GRM21BR60J106KE19L
GRM188R60J475KE19
but a minimum
SP7685, 1.2A Buck/BoostCharge Pump LED Driver
C1005X5R0J105M
C2012X5R0J106M
C1608X5R0J475K
Part Number
OUT
pins as
9
The sense resistor R
the value needed in the Torch mode for the
desired output current by the equation:
R
Mode)
Once the R
for Torch mode, the V
selected for Flash mode using the following
equation:
V
for Flash Mode.
Next, the R
Flash mode using the following equation:
R
For an example of 200mA Torch mode and
700mA Flash mode, the values R
0.22Ω, V
=56KΩ are calculated. The power obtained
in the Flash mode would be:
P
The typical 0603 surface mount resistor is
rated 1/10 Watt continuous power and 1/5
Capacitance/
FB
FLASH
SENSE
SET
4.7uF/6.3V
4.7uF/6.3V
10uF/6.3V
10uF/6.3V
1uF/6.3V
1uF/6.3V
= I
Voltage
=
OUT
= V
= V
(
14uA
V
FB
FB
* R
FB
FB
= 155mV (Flash Mode), and R
* I
SENSE
SET
/ I
SENSE
OUT
)
OUT
COMPONENT SELECTION
* 5 Ω (Flash Mode)
resistor can be selected for
= 155mV * 700mA = 109mW.
0805/X5R/1.35mm
0402/X5R/0.55mm
0805/X5R/1.35mm
resistor has been selected
0402/X5R/0.5mm
0603/X5R/0.9mm
0603/X5R/0.9mm
Type/Thickness
where V
(Flash Mode) where I
RESISTOR SELECTION
CapacitorSize/
SENSE
FB
FB
is determined by
© 2006 Sipex Corporation
voltage can be
= 50mV (Torch
@100kHz
SENSE
ESR
0.03
0.02
0.02
0.03
0.02
0.02
OUT
SET
is
=