SEMTECH SC621AULTRT

SC621A
LED Light Management Unit
Charge Pump, 4 LEDs, 400mA Flash LED,
Dual LDOs, and I2C Interface
POWER MANAGEMENT
Features
Description
„
The SC621A is a high efficiency charge pump LED driver
using Semtech’s proprietary mAhXLifeTM technology.
Performance is optimized for use in single-cell Li-ion
battery applications.
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Input supply voltage range — 3.0V to 5.5V
Charge pump modes — 1x, 1.5x and 2x
Four programmable current sinks with 32 steps from
0.5mA to 25mA
Flash LED — 400mA max in flash mode, 250mA max
continuous for spotlight
Two user-configurable 100mA low-noise LDO
regulators
Charge pump frequency — 250kHz
I2C compatible interface — up to 400kHz
Backlight current accuracy ±1.5% typical
Backlight current matching ±0.5% typical
Programmable fade-in/fade-out for main backlight
External flash control pin to sync with camera
Optional 1s flash time out
Automatic sleep mode (LEDs off ) — IQ = 100μA
Low shutdown current — 0.1μA (typical)
Ultra-thin package — 3mm x 3mm x 0.6mm
Fully WEEE and RoHS compliant
The charge pump provides backlight current in
conjunction with four matched current sinks. It also can
supply continuous or bursted current to a flash LED using
the dedicated flash driver current sink. The load and
supply conditions determine whether the charge pump
operates in 1x, 1.5x, or 2x mode. An optional fading feature
that gradually adjusts the backlight current is provided to
simplify control software. A flash-timeout feature disables
the flash if active for longer than 1 second. The SC621A also
provides two low-dropout, low-noise linear regulators for
powering a camera module or other peripheral circuits.
The SC621A uses an I2C compatible serial interface. The
interface controls all functions of the device, including
backlight and flash currents as well as two LDO voltage
outputs. The flash/spotlight output is triggered via either
the I2C interface or a dedicated pin.
Applications
„
Cellular phone backlighting and flash
„ PDA backlighting and flash
„ Camera I/O and core power
In sleep mode, the device reduces quiescent current to
100μA while continuing to monitor the serial interface.
The two LDOs can be enabled when the device is in sleep
mode. Total current reduces to 0.1μA in shutdown.
Typical Application Circuit
MAIN BACKLIGHT
VIN
VBAT
CIN
2.2μF
I2C Data
SDA
I2C Clock
SCL
Flash Control
Enable Control
VOUT
SC621A
FLEN
COUT
4.7μF
BL 1
BL 2
BL 3
BL 4
EN
BYP
CBYP
22nF
FLASH
FL
AGND
LDO 1
PGND
LDO 2
C1+
C1
2.2μF
C1-
C2+ C2-
VLDO1 = 2.5V to 3.3V
VLDO2 = 1.5V to 1.8V
CLDO1
1μF
CLDO2
1μF
C2
2.2μF
US Patents: 6,504,422; 6,794,926
June 27, 2007
© 2007 Semtech Corporation
1
SC621A
C2-
VIN
C1+
C2+
VOUT
Ordering Information
C1-
Pin Configuration
20
19
18
17
16
1
TOP VIEW
15
LDO1
14
LDO2
PGND
2
FL
3
13
BYP
BL1
4
12
EN
BL2
5
11
SDA
6
7
8
9
10
BL3
BL4
AGND
SCL
FLEN
T
Device
Package
SC621AULTRT(1)(2)
MLPQ-UT-20 3×3
SC621AEVB
Evaluation Board
Notes:
(1) Available in tape and reel only. A reel contains 3,000 devices.
(2) Available in lead-free package only. Device is WEEE and RoHS
compliant.
MLPQ-UT-20; 3x3, 20 LEAD
θJA = 35°C/W
Marking Information
621A
yyww
xxxx
yyww = Date Code
xxxx = Semtech Lot No.
2
SC621A
Absolute Maximum Ratings
Recommended Operating Conditions
VIN (V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to +6.0
Ambient Temperature Range (°C) . . . . . . . . -40 < TA < +85
VOUT (V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to +6.0
VIN (V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.0 < VIN < 5.5
C1+, C2+ (V) . . . . . . . . . . . . . . . . . . . . . . . -0.3 to (VOUT + 0.3)
VOUT (V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 < VOUT < 5.25
Pin Voltage - All Other Pins (V) . . . . . . . . . . . -0.3 to (VIN + 0.3)
Voltage Difference between any two LEDs (V) . . . . . . < 1.2
VOUT Short Circuit Duration . . . . . . . . . . . . . . . . Continuous
VLDO1, VLDO2 Short Circuit Duration. . . . . . . Continuous
ESD Protection Level(1) (kV) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Thermal Information
Thermal Resistance, Junction to Ambient(2) (°C/W) . . . . 35
Maximum Junction Temperature (°C) . . . . . . . . . . . . . . +150
Storage Temperature Range (°C) . . . . . . . . . . . . -65 to +150
Peak IR Reflow Temperature (10s to 30s) (°C) . . . . . . . +260
Exceeding the above specifications may result in permanent damage to the device or device malfunction. Operation outside of the parameters
specified in the Electrical Characteristics section is not recommended.
NOTES:
(1) Tested according to JEDEC standard JESD22-A114-B.
(2) Calculated from package in still air, mounted to 3” x 4.5”, 4 layer FR4 PCB with thermal vias under the exposed pad per JESD51 standards.
Electrical Characteristics
Unless otherwise noted, TA = +25°C for Typ, -40ºC to +85°C for Min and Max, TJ(MAX) = 125ºC, VIN = 3.0V to 4.2V, CIN= C1= C2= 2.2μF,
COUT = 4.7μF (ESR = 0.03Ω), ΔVF ≤ 1.2V(1)
Parameter
Symbol
Conditions
IQ(OFF)
Min
Typ
Max
Units
Shutdown, VIN = 4.2V
0.1
2
μA
Sleep (LDOs off ), EN = VIN
100
160
Sleep (LDOs on), EN = VIN,
VIN > (VLDO + 300mV), ILDO < 200mA
220
340
Charge pump in 1x mode, 4 backlights on
3.8
4.65
Charge pump in 1.5x mode, 4 backlights on
4.6
5.85
Charge pump in 2x mode, 4 backlights on
4.6
5.85
VOUT pin shorted to GND
300
mA
160
°C
Supply Specifications
Shutdown Current
Total Quiescent Current
IQ
μA
mA
Fault Protection
Output Short Circuit
Current Limit
Over-Temperature
Flash Mode Safety Timer(2)
IOUT(SC)
TOTP
tFL(MAX)
Flash sink active
0.75
1.00
1.25
s
3
SC621A
Electrical Characteristics (continued)
Parameter
Symbol
Conditions
Min
Typ
Max
Units
VOVP
VOUT pin open circuit, VOUT = VOVP
rising threshold
5.3
5.7
6.0
V
VUVLO
Decreasing VIN
Fault Protection (continued)
Charge Pump
Over-Voltage Protection
2.4
V
300
mV
Undervoltage Lockout
VUVLO-HYS
Charge Pump Electrical Specifications
Maximum Total Output
Current
IOUT(MAX)
VIN > 3.4V, sum of all active LED currents,
VOUT(MAX) = 4.0V
500
Backlight Current Setting
IBL
Nominal setting for BL1 thru BL4
0.5
25
mA
Flash Current Setting
IFL
Nominal setting for FL
50
400
mA
Backlight Current Accuracy
IBL_ACC
VIN = 3.7V, IBL = 12mA, TA = 25°C
-8
±1.5
+8
%
Backlight Current Matching
IBL-BL
VIN = 3.7V, IBL = 12mA(3)
-3.5
±0.5
+3.5
%
Flash Current Accuracy
IFL_ACC
VIN = 3.7V, IFL = 400mA, TA = 25°C
-15
+15
%
1x Mode to 1.5x Mode
Falling Transition Voltage
V TRANS1x
IOUT = 40mA, IBLn = 10mA, VOUT = 3.2V
3.27
V
1.5x Mode to 1x Mode
Hysteresis
VHYST1x
IOUT = 40mA, IBLn = 10mA, VOUT = 3.2V
250
mV
1.5x Mode to 2x Mode
Falling Transition Voltage
V TRANS1.5x
IOUT = 40mA, IBLn = 10mA, VOUT = 4.0V(4)
2.92
V
2x Mode to 1.5x Mode
Hysteresis
VHYST1.5x
IOUT = 40mA, IBLn = 10mA, VOUT = 4.0V(4)
300
mV
Current Sink Off-State
Leakage Current
IBLn
VIN = VBLn = 4.2V
0.1
fPUMP
VIN = 3.2V
250
LDO1 Voltage Setting
VLDO1
Range of nominal settings
in 100mV increments
2.5
3.3
V
LDO2 Voltage Setting
VLDO2
Range of nominal settings
in 100mV increments
1.5
1.8
V
LDO1, LDO2 Output
Voltage Accuracy
VLDO1, VLDO2
VIN = 3.7V, ILDO = 1mA
-3.5
±3
+3.5
%
2.1
7.2
Pump Frequency
mA
1
μA
kHz
LDO Electrical Specifications
LDO1, ILDO1 = 1mA, VOUT = 2.8V
Line Regulation
ΔVLINE
mV
LDO2, ILDO2 = 1mA, VOUT = 1.8V
1.3
4.8
4
SC621A
Electrical Characteristics (continued)
Parameter
Symbol
Conditions
Min
Typ
Max
Units
LDO Electrical Specifications (continued)
Load Regulation
ΔVLOAD
Dropout Voltage(5)
VD
Current Limit
ILIM
Power Supply
Rejection Ratio
25
VLDO2 = 1.8V, VIN = 3.7V,
ILDO2 = 1mA to 100 mA
20
mV
ILDO1 = 100mA
100
150
200
mV
mA
PSRRLDO1
2.5V < VLDO1 < 3V, f < 1kHz, CBYP = 22nF, ILDO1 = 50mA,
VIN = 3.7V with 0.5VP-P ripple
50
PSRRLDO2
f < 1kHz, CBYP = 22nF, ILDO2 = 50mA,
VIN = 3.7V with 0.5VP-P ripple
60
en-LDO1
LDO1, 10Hz < f < 100kHz, CBYP = 22nF, CLDO = 1μF,
ILDO1 = 50 mA, VIN = 3.7V, 2.5V < VLDO1 < 3V
100
en-LDO2
LDO2, 10Hz < f < 100kHz, CBYP = 22nF,
CLDO = 1μF, ILDO2 = 50 mA, VIN = 3.7V
50
Output Voltage Noise
Minimum Output Capacitor
VLDO1 = 3.3V, VIN = 3.7V,
ILDO1 = 1mA to 100 mA
dB
μVRMS
CLDO(MIN)
1
μF
Digital I/O Electrical Specifications (FLEN, EN)
Input High Threshold
VIH
VIN = 5.5V
Input Low Threshold
VIL
VIN = 3.0V
Input High Current
IIH
VIN = 5.5V
Input Low Current
IIL
VIN = 5.5V
1.6
V
0.4
V
-1
+1
μA
-1
+1
μA
0.4
V
I2C Interface
Interface complies with slave mode I2C interface as described by Philips I2C specification version 2.1 dated January, 2000.
VB-IL
Digital Input Voltage
VB-IH
1.6
V
IDIN (SDA) ≤ 3mA
SDA Output Low Level
-0.2
0.4
V
0.2
μA
Digital Input Current
IB-IN
Hysteresis of
Schmitt Trigger Inputs
VHYS
0.1
V
Maximum Glitch Pulse
Rejection
tSP
50
ns
5
SC621A
Electrical Characteristics (continued)
Parameter
Symbol
Conditions
Min
Typ
Max
Units
I2C Interface (Continued)
CIN
10
Clock Frequency
fSCL
400
SCL Low Period(6)
tLOW
1.3
μs
SCL High Period(6)
tHIGH
0.6
μs
Data Hold Time(6)
tHD_DAT
0
μs
Data Setup Time(6)
tSU_DAT
100
μs
Setup Time for Repeated
START Condition(6)
tSU_STA
0.6
μs
Hold Time for Repeated
START Condition(6)
tHD_STA
0.6
μs
Setup Time for STOP
Condition(6)
tSU_STO
0.6
μs
Bus-Free Time Between
STOP and START(6)
tBUF
1.3
μs
Interface Start-up Time(6)
tEN
I/O Pin Capacitance
pF
I2C Timing
Bus Start-up Time After EN Pin is Pulled High
440
1
kHz
ms
Notes:
(1) ΔVF is the voltage difference between any two LEDs.
(2) Once tripped, flash output will remain disabled until FLEN pin is cycled or reset via serial interface.
(3) Current matching equals ± [IBL(MAX) - IBL(MIN] / [IBL(MAX) + IBL(MIN)].
(4) Test voltage is VOUT = 4.0V — a relatively extreme LED voltage — to force a transition during test. Typically VOUT = 3.2V for white LEDs.
(5) Dropout is defined as (VIN - VLDO1) when VLDO1 drops 100mV from nominal. Dropout does not apply to LDO2 since it has a maximum output voltage
of 1.8V.
(6) Guaranteed by design
6
SC621A
Typical Characteristics
Battery Current (4 LEDs) — 25mA Each
160
Battery Current (4 LEDs) — 12mA Each
VOUT=3.66V, IOUT=100mA, 25°C
80
73
Battery Current (mA)
Battery Current (mA)
150
140
130
120
66
59
52
110
100
4.2
4.0
3.8
3.6
VIN (V)
3.4
3.2
45
4.2
3.0
Backlight Efficiency (4 LEDs) — 25mA Each
100
100
% Efficiency
% Efficiency
3.8
3.6
VIN (V)
3.4
3.2
3.0
VOUT=3.50V, IOUT=48mA, 25°C
90
80
70
80
70
60
60
50
4.2
4.0
3.8
3.6
VIN (V)
3.4
3.2
50
4.2
3.0
3.8
3.6
3.4
3.2
3.0
Backlight Efficiency (4 LEDs) — 5.0mA Each
VOUT=3.33V, IOUT=20mA, 25°C
100
35
VOUT=3.33V, IOUT=20mA, 25°C
% Efficiency
90
30
25
80
70
60
20
15
4.2
4.0
VIN (V)
Battery Current (4 LEDs) — 5.0mA Each
Battery Current (mA)
4.0
Backlight Efficiency (4 LEDs) — 12mA Each
VOUT=3.66V, IOUT=100mA, 25°C
90
40
VOUT=3.50V, IOUT=48mA, 25°C
4.0
3.8
3.6
VIN (V)
3.4
3.2
3.0
50
4.2
4.0
3.8
3.6
VIN (V)
3.4
3.2
3.0
7
SC621A
Typical Characteristics (continued)
Flash Current — 300mA
390
Flash Current — 400mA
VOUT=3.58V at 25°C
490
460
Flash Current (mA)
360
Flash Current (mA)
VOUT=3.39V at 25°C
330
300
270
430
400
370
340
240
210
4.2
4.0
3.8
3.6
VIN (V)
3.4
3.2
310
4.2
3.0
Spotlight Current — 50mA
53
340
3.6
VIN (V)
3.4
3.2
3.0
3.2
3.0
VOUT=3.50V at 25°C
310
Spotlight Current (mA)
Spotlight Current (mA)
3.8
Spotlight Current — 250mA
VOUT=3.02V at 25°C
52
51
50
49
48
280
250
220
190
47
4.2
4.0
3.8
3.6
VIN (V)
3.4
3.2
160
4.2
3.0
0
VIN=3.7V at 25°C, ILDO1=50mA, VLDO1=2.8V
0
-10
-20
-20
PSRR (dB)
-10
-30
-40
-60
-60
-70
1000
Frequency (Hz)
3.6
VIN (V)
3.4
10000
VIN=3.7V at 25°C, ILDO2=50mA, VLDO2=1.8V
-40
-50
100
3.8
-30
-50
10
4.0
PSRR vs. Frequency (LDO2)
PSRR vs. Frequency (LDO1)
PSRR (dB)
4.0
-70
10
100
Frequency (Hz)
1000
10000
8
SC621A
Typical Characteristics (continued)
Load Regulation (LDO2)
Load Regulation (LDO1)
24
VLDO1=3.3V, VIN=3.7V, 25°C
24
16
Output Voltage Variation (mV)
Output Voltage Variation (mV)
16
VLDO2=1.8V, VIN=3.7V, 25°C
8
0
-8
-16
8
0
-8
-16
-24
-24
0
30
60
90
120
150
0
ILDO1(mA)
100
80
60
Noise (μV)
Noise (μV)
VLDO1=2.8V, VIN=3.7V, 25°C
80
70
60
150
40
20
0
20
40
60
80
0
100
0
20
2
Output Voltage Variation (mV)
1
0
-1
-2
4.0
3.8
3.6
VIN (V)
60
80
100
Line Regulation (LDO2)
VLDO1=2.8V, ILDO1=1mA, 25°C
-3
4.2
40
ILDO2 (mA)
Line Regulation (LDO1)
Output Voltage Variation (mV)
120
VLDO2=1.8V, VIN=3.7V, 25°C
ILDO1 (mA)
2
90
Noise vs Load Current (LDO2)
90
50
60
ILDO2(mA)
Noise vs Load Current (LDO1)
100
30
3.4
3.2
3.0
VLDO2=1.8V, ILDO2=1mA, 25°C
1
0
-1
-2
-3
4.2
4.0
3.8
3.6
VIN (V)
3.4
3.2
3.0
9
SC621A
Typical Characteristics (continued)
Load Transient Response (LDO1) — Rising Edge
Load Transient Response (LDO2) — Rising Edge
VIN=3.7V, VLDO1=2.8V, ILDO1=1 to 100mA
VIN=3.7V, VLDO2=1.8V, ILDO2=1 to 100mA
VLDO1 (50mV/div)
VLDO2 (50mV/div)
ILDO1 (100mA/div)
ILDO2 (100mA/div)
Time (20μs/div)
Load Transient Response (LDO1) — Falling Edge
Time (20μs/div)
Load Transient Response (LDO2) — Falling Edge
VIN=3.7V, VLDO2=1.8V, ILDO2=100 to 1mA
VIN=3.7V, VLDO1=2.8V, ILDO1=100 to 1mA
VLDO1 (50mV/div)
VLDO2 (50mV/div)
ILDO1 (100mA/div)
ILDO2 (100mA/div)
Time (200μs/div)
Time (200μs/div)
10
SC621A
Typical Characteristics (continued)
Output Short Circuit Current Limit
Flash Mode Safety Timer
VOUT=0V, VIN=4.2V, 25°C
VOUT (1V/div)
VIN=3.7V, 25°C
VFLEN (5V/div)
VOUT (2V/div)
IOUT (100mA/div)
IFL (200mA/div)
Time (1ms/div)
Time (200ms/div)
Output Open Circuit Protection
Flash Current Pulse
IFL=400mA, VIN=3.7V, VOUT=3.7V, 25°C
VIN=3.7V, 25°C
VFLEN (5V/div)
VBL1 (500mV/div)
VOUT (2V/div)
VOUT (2V/div)
IBL1 (20mA/div)
IFL (200mA/div)
Time (200μs/div)
Time (40ms/div)
11
SC621A
Pin Descriptions
Pin #
Pin Name
Pin Function
1
C2-
2
PGND
3
FL
Current sink output for flash LED(s)
4
BL1
Current sink output for main backlight LED 1 — leave this pin open if unused
5
BL2
Current sink output for main backlight LED 2 — leave this pin open if unused
6
BL3
Current sink output for main backlight LED 3 — leave this pin open if unused
7
BL4
Current sink output for main backlight LED 4 — leave this pin open if unused
8
AGND
9
SCL
I2C clock input pin
10
FLEN
Control pin for flash LED(s) — high = ON, low = OFF
11
SDA
I2C bi-directional data pin — used for read and write operations for all internal registers (refer to
Register Map and I2C Interface sections)
12
EN
Chip enable — active high — low state resets all registers (see register map table)
13
BYP
Bypass pin for voltage reference — connect with a 22nF capacitor to AGND
14
LDO2
Output of LDO2 — connect with a 1μF capacitor to AGND
15
LDO1
Output of LDO1 — connect with a 1μF capacitor to AGND
16
VOUT
Charge pump output — all LED anode pins should be connected to this pin — requires a 4.7μF
capacitor to PGND
17
C2+
Positive connection to bucket capacitor 2 — requires a 2.2μF capacitor connected to C2-
18
C1+
Positive connection to bucket capacitor 1 — requires a 2.2μF capacitor connected to C1-
19
VIN
Battery voltage input — connect with a 2.2μF capacitor to PGND
20
C1-
Negative connection to bucket capacitor 1 — requires a 2.2μF capacitor connected to C1+
T
THERMAL PAD
Negative connection to bucket capacitor 2 — requires a 2.2μF capacitor connected to C2+
Ground pin for high current charge pump and Flash LED driver
Analog ground pin — connect to ground and separate from PGND current
Thermal pad for heatsinking purposes — connect to ground plane using multiple
vias — not connected internally
12
SC621A
Block Diagram
VIN
19
EN
12
SDA
11
FLEN
10
SCL
9
BYP
13
VIN
I2 C
Compatible
Interface
and Logic
Control
C1+
C1-
C2+
C2-
18
20
17
1
VOUT
mAhXLifeTM Fractional
Charge Pump
(1x, 1.5x, 2x)
VOUT
2
PGND
4
BL1
5
BL2
6
BL3
7
BL4
3
FL
Oscillator
Current
Setting
DAC
Bandgap
Reference
16
Voltage
Setting
DAC
VIN
LDO1
15
LDO1
14
LDO2
VIN
LDO2
AGND
8
13
SC621A
Applications Information
General Description
This design is optimized for handheld applications
supplied from a single Li-Ion cell and includes the
following key features:
•
•
•
•
•
A high efficiency fractional charge pump that
supplies power to all LEDs
Four matched current sinks that control LED
backlighting current, with 0.5mA to 25mA per
LED
An LED flash output that provides up to 400mA
of momentary current or up to 250mA of
continuous spotlight current
Two adjustable LDOs with outputs ranging from
2.5V to 3.3V for LDO1 and 1.5V to 1.8V for LDO2,
adjustable in 100mV increments
An I2C compatible interface that provides control
of all device functions
High Current Fractional Charge Pump
The backlight and flash outputs are supported by a high
efficiency, high current fractional charge pump output
at the VOUT pin. The charge pump multiplies the input
voltage by 1, 1.5, or 2 times. The charge pump switches
at a fixed frequency of 250kHz in 1.5x and 2x modes
and is disabled in 1x mode to save power and improve
efficiency.
The mode selection circuit automatically selects the
1x, 1.5x or 2x mode based on circuit conditions. Circuit
conditions such as low input voltage, high output current,
or high LED voltage place a higher demand on the charge
pump output. A higher numerical mode may be needed
momentarily to maintain regulation at the VOUT pin
during intervals of high demand, such as the high current
of an LED flash or the droop at the VIN pin during a supply
voltage transient. The charge pump responds to these
momentary high demands, setting the charge pump to
the optimum mode (1x, 1.5x or 2x), as needed to deliver
the output voltage and load current while optimizing
efficiency. Hysteresis is provided to prevent mode
toggling.
between the C1+ and C1- pins and the other must be
connected between the C2+ and C2- pins as shown
in the typical application circuit diagram. These
capacitors should be equal in value, with a minimum
capacitance of 2.2μF to support the charge pump
current requirements. The device also requires a 2.2μF
capacitor on the VIN pin and a 4.7μF capacitor on the
VOUT pin to minimize noise and support the output
drive requirements. Capacitors with X7R or X5R ceramic
dielectric are strongly recommended for their low ESR
and superior temperature and voltage characteristics.
Y5V capacitors should not be used as their temperature
coefficients make them unsuitable for this application.
LED Backlight Current Sinks
The backlight current is set via the I2C compatible
interface. The current is regulated to one of 32 values
between 0.5mA and 25mA. The step size varies depending
upon the current setting. Between 0.5mA and 12mA, the
step size is 0.5mA. The step size increases to 1mA for
settings between 12mA and 15mA and 2mA for settings
greater than 15mA. This feature allows finer adjustment
for dimming functions in the low current setting range
and coarse adjustment at higher current settings where
small current changes are not visibly noticeable in LED
brightness.
All backlight current sinks have matched currents, even
when there is variation in the forward voltages (ΔVF )
of the LEDs. A ΔVF of 1.2V is supported when the input
voltage is at 3.0V. Higher ΔVF LED mis-match is supported
when VIN is higher than 3.0V. All current sink outputs are
compared and the lowest output is used for setting the
voltage regulation at the VOUT pin. This is done to ensure
that sufficient bias exists for all LEDs, including the flash
LED.
The backlight LEDs default to the off state upon powerup. For backlight applications using less than four LEDs,
any unused output must be left open and the unused
LED driver must remain disabled. When writing to the
Backlight Enable Control register, a zero (0) must be
written to the corresponding bit of any unused output.
The charge pump requires two bucket capacitors for
low ripple operation. One capacitor must be connected
14
SC621A
Applications Information (continued)
Backlight Quiescent Current
The quiescent current required to operate all four
backlights is reduced by 1.5mA when backlight current
is set to 4.0mA or less. This feature results in higher
efficiency under light-load conditions. Further reduction
in quiescent current will result from using fewer than four
LEDs.
Fade-In and Fade-Out
Backlight brightness can be set to automatically fade-in
when current is set to increase and fade-out when current
is set to decrease. When enabled with a new current
setting, the current will step through each incremental
setting between the old and new values. The result is a
visually smooth change in brightness with a rate of fade
that can be set to 8, 16, 24, or 32 ms per step.
LED Flash and Spotlight Current Sink
A single output current sink is provided to drive both flash
and spotlight functions. In flash mode, this current sink
provides up to 400mA for a flash LED or array of parallel
LEDs. Flash current settings are in 50mA increments from
50mA to 400mA. The FLEN pin directly triggers the FLASH
function when pulled high, or it can be wired to VIN to
enable software control via the serial interface.
In spotlight mode, the output can be set for up to 250mA
of continuous current. Settings are available in 50mA
increments from 50mA to 250mA. Continuous operation
above 250mA is not recommended due to high power
dissipation.
Flash and Spotlight Safety Timer
A safety timer disables the flash and spotlight output
current sink if the sink remains active for an extended
period. The timer protects the SC621A and the LED from
high power dissipation that can cause overheating. The
timer’s default state is on, but the timer may be disabled
via the serial interface to allow continuous output current
in spotlight mode. The safety timer affects only the FL pin
and will turn off the sink after a period of 1 second. The
timer may be reset by either forcing the FLEN pin low
or by resetting the Flash/Spotlight control bits via the
interface.
Programmable LDO Outputs
Two low dropout (LDO) regulators are provided for
camera module I/O and core power. Each LDO has at least
100mA of available load current with ±3.5% accuracy. The
minimum current limit is 200mA, so outputs greater than
100mA are possible at somewhat reduced accuracy.
A 1μF, low ESR capacitor should be used as a bypass
capacitor on each LDO output to reduce noise and
ensure stability. In addition, it is recommended that a
minimum 22nF capacitor be connected from the BYP
pin to ground to minimize noise and achieve optimum
power supply rejection. A larger capacitor can be used
for this function, but at the expense of increasing turnon time. Capacitors with X7R or X5R ceramic dielectric
are strongly recommended for their low ESR and superior
temperature and voltage characteristics. Y5V capacitors
should not be used as their temperature coefficients
make them unsuitable for this application.
Shutdown State
The device is disabled when the EN pin is low. All registers
are reset to default condition when EN is low.
Sleep Mode
When all LEDs are off, sleep mode is activated. This is a
reduced current mode that helps minimize overall current
consumption by turning off the clock and the charge
pump while continuing to monitor the serial interface for
commands. Both LDOs can be powered up while in sleep
mode.
I2C Compatible Interface Functions
All device functions can be controlled via the I2C
compatible interface. The interface is described in detail
in the Serial Interface section of the datasheet.
15
SC621A
Applications Information (continued)
Protection Features
The SC621A provides several protection features to
safeguard the device from catastrophic failures. These
features include:
•
•
•
•
•
Output Open Circuit Protection
Over-Temperature Protection
Charge Pump Output Current Limit
LDO Current Limit
LED Float Detection
Output Open Circuit Protection
Over-Voltage Protection (OVP) is provided at the VOUT
pin to prevent the charge pump from producing an
excessively high output voltage. In the event of an open
circuit at VOUT, the charge pump runs in open loop and
the voltage rises up to the OVP limit. OVP operation is
hysteretic, meaning the charge pump will momentarily
turn off until VOUT is sufficiently reduced. The maximum
OVP threshold is 6.0V, allowing the use of a ceramic
output capacitor rated at 6.3V with no fear of over-voltage
damage.
Over-Temperature Protection
The Over-Temperature (OT) protection circuit helps
prevent the device from overheating and experiencing
a catastrophic failure. When the junction temperature
exceeds 160°C, the device goes into thermal shutdown
with all outputs disabled until the junction temperature
is reduced. All register information is retained during
thermal shutdown.
Charge Pump Output Current Limit
The device also limits the charge pump current at the
VOUT pin. When VOUT is shorted to ground, the typical
output current is 300mA. The current limiting is triggered
by an output under-voltage lockout below 2V. The output
returns to normal when the short is removed and VOUT is
above 2.5V. Above 2.5V, a typical current limit of 300mA
applies when the FL current sink is off and a typical current
limit of 1A applies when the FL current sink is on.
LDO Current Limit
The device limits the output currents of LDO1 and LDO2 to
help prevent it from overheating and to protect the loads.
The minimum limit is 200mA, so load current greater than
the rated 100mA can be used with degraded accuracy
and larger dropout without tripping the current limit.
LED Float Detection
Float detect is a fault detection feature of the LED current
sink outputs. If an output is programmed to be enabled
and an open circuit fault occurs at any current sink output,
that output will be disabled to prevent a sustained output
OVP condition from occurring due to the resulting open
loop. Float detect ensures device protection but does
not ensure optimum performance. Unused LED outputs
must be disabled to prevent an open circuit fault from
occurring.
16
SC621A
Applications Information (continued)
•
PCB Layout Considerations
The layout diagram in Figure 1 illustrates a proper
two-layer PCB layout for the SC621A and supporting
components. Following fundamental layout rules is
critical for achieving the performance specified in the
Electrical Characteristics table. The following guidelines
are recommended when developing a PCB layout:
GND
C1+
CLDO1
C2-
LDO1
PGND
LDO2
SC621A
FL
•
COUT
C2
C2+
C1-
C1
VOUT
CIN
•
VOUT
VIN
GND
CLDO2
Figure 2 — Layer 1
BYP
BL1
EN
BL2
SDA
FLEN
SCL
BL3
CBYP
AGND
•
VIN
•
Place all bypass and decoupling capacitors —
C1, C2, CIN, COUT, CLDO1, CLDO2, and CBYP as
close to the device as possible.
All charge pump current passes through VIN,
VOUT, and the bucket capacitor connection
pins. Ensure that all connections to these pins
make use of wide traces so that the resistive
drop on each connection is minimized.
The thermal pad should be connected to the
ground plane using multiple vias to ensure
proper thermal connection for optimal heat
transfer.
BL4
•
•
Make all ground connections to a solid
ground plane as shown in the example layout
(Figure 3).
If a ground layer is not feasible, the following
groupings should be connected:
ƒ PGND — CIN, COUT
ƒ AGND — Ground Pad, CLDO1, CLDO2,
CBYP
If no ground plane is available, PGND and
AGND should be routed back to the negative
battery terminal as separate signals using thick
traces. Joining the two ground returns at the
terminal prevents large pulsed return currents
from mixing with the low-noise return currents
of the LDOs.
Both LDO output traces should be made as
wide as possible to minimize resistive losses.
Figure 1 — Recommended PCB Layout
Figure 3 — Layer 2
17
SC621A
Register Map
Address
D7
D6
D5
D4
D3
D2
D1
D0
Reset
Value
Description
0x00
FADE_1
FADE_0
FADE_EN
BL_4
BL_3
BL_2
BL_1
BL_0
0x00
Backlight
Current
Control
0x01
0(1)
0(1)
0(1)
0(1)
BLEN_4
BLEN_3
BLEN_2
BLEN_1
0x00
Backlight
Enable Control
0x02
0(1)
0(1)
0(1)
FLTO
FL_2
FL_1
FL_0
FL/SPLB
0x10
Flash/Spotlight
Control
0x03
0(1)
LDO2_2
LDO2_1
LDO2_0
LDO1_3
LDO1_2
LDO1_1
LDO1_0
0x00
LDO Control
Notes:
(1) 0 = always write a 0 to these bits
Register and Bit Definitions
Backlight Current Control Register (0x00)
This register is used to set the currents for the backlight
current sinks, as well as to enable and set the fade step
rate. These current sinks need to be enabled in the
Backlight Enable Control register to be active.
FADE[1:0]
These bits are used to set the rise/fall rate between two
backlight currents as follows:
FADE_1
FADE_0
Fade Feature
Rise/Fall Rate
(ms/step)
0
0
32
0
1
24
1
0
16
1
1
8
value to a new value set by bits BL[4:0] at a rate of 8ms to
32ms per step. A new backlight level cannot be written
during an ongoing fade operation, but an ongoing fade
operation may be cancelled by resetting the fade bit.
Clearing the fade bit during an ongoing fade operation
changes the backlight current immediately to the value
of BL[4:0]. The number of counts to complete a fade
operation equals the difference between the old and new
backlight values to increment or decrement the BL[4:0]
bits. If the fade bit is cleared, the current level will change
immediately without the fade delay. The rate of fade may
be changed dynamically, even while a fade operation is
active, by writing new values to the FADE_1 and FADE_0
bits. The total fade time is determined by the number of
steps between old and new backlight values, multiplied
by the rate of fade in ms/step. The longest elapsed time
for a full scale fade-out of the backlight is nominally 1.024
seconds when the default interval of 32ms is used.
The number of steps in changing the backlight current will
be equal to the change in binary count of bits BL[4:0].
FADE_EN
This bit is used to enable or disable the fade feature. When
the fade function is enabled and a new backlight current
is set, the backlight current will change from its current
18
SC621A
Register and Bit Definitions (continued)
BL[4:0]
These bits are used to set the current for the backlight
current sinks. All enabled backlight current sinks will sink
the same current, as shown in Table 1.
Table 1 — Backlight Current Control Bits
BL_4 BL_3 BL_2 BL_1 BL_0
Backlight Current
(mA)
0
0
0
0
0
0.5
0
0
0
0
1
1.0
0
0
0
1
0
1.5
0
0
0
1
1
2.0
0
0
1
0
0
2.5
0
0
1
0
1
3.0
0
0
1
1
0
3.5
0
0
1
1
1
4.0
0
1
0
0
0
4.5
0
1
0
0
1
5
0
1
0
1
0
5.5
0
1
0
1
1
6
0
1
1
0
0
6.5
0
1
1
0
1
7
0
1
1
1
0
7.5
0
1
1
1
1
8
1
0
0
0
0
8.5
1
0
0
0
1
9
1
0
0
1
0
9.5
1
0
0
1
1
10
1
0
1
0
0
10.5
1
0
1
0
1
11
1
0
1
1
0
11.5
1
0
1
1
1
12
1
1
0
0
0
13
1
1
0
0
1
14
1
1
0
1
0
15
1
1
0
1
1
17
1
1
1
0
0
19
1
1
1
0
1
21
1
1
1
1
0
23
1
1
1
1
1
25
BL Enable Control Register (0x01)
This register is used to enable the backlight current
sinks.
BLEN[4:1]
These bits are used to enable current sinks (active high,
default low).
BLEN_4 — Enable bit for backlight BL4
BLEN_3 — Enable bit for backlight BL3
BLEN_2 — Enable bit for backlight BL2
BLEN_1 — Enable bit for backlight BL1
When enabled, the current sinks will carry the current set
by the backlight current control bits BL[4:0], as shown in
Table 1.
Flash/Spotlight Control Register (0x02)
This register is used to configure the flash time-out feature,
the flash or spotlight current, and select flash or spotlight
current ranges.
FLTO
This bit is used to enable the flash safety time-out feature.
The default state is enabled with FLTO = 1. If this bit is set,
the device will turn off the flash after a nominal period of
1s. Two ways to re-enable the flash function after a safety
time-out are:
Pull the FLEN pin low to re-enable the flash
function
Clear and re-write FL[2:0]
•
•
FL[2:0]
These bits are used to set the current for the flash current
sink when configured for flash or spotlight by the FL/SPLB
bit. Bits FL[2:0] set the flash or spotlight current, as shown
in Table 2.
19
SC621A
Register and Bit Definitions (continued)
Table 2 — Flash/Spotlight Control Bits
FL_2
FL_1
FL_0
FL/
SPLB
Flash/Spotlight
Current (mA)
0
0
0
0
OFF
0
0
1
0
50
0
1
0
0
0
1
1
1
0
1
LDO2[2:0]
These bits are used to set the output voltage of LDO2, as
shown in Table 3.
Table 3 — LDO2 Control Bits
LDO2_2
LDO2_1
LDO2_0
LDO2
Output Voltage
100
0
0
0
OFF
0
150
0
0
1
1.8V
0
0
200
0
1
0
1.7V
0
1
0
250
0
1
1
1.6V
1
1
0
0
250
1
0
0
1.5V
1
1
1
0
250
0
0
0
1
OFF
0
0
1
1
300(1)
0
1
0
1
350(1)
LDO1[3:0]
These bits set the output voltage of LDO1, as shown in
Table 4.
0
1
1
1
400(1)
Table 4 — LDO1 Control Bits
1
0
0
1
400(1)
1
0
1
1
400(1)
1
1
0
1
400(1)
1
1
1
1
400(1)
Note:
(1) When on continuously, the device may reach the temperature
limit with 300mA and higher.
FL/SPLB
This bit is used to select either the flash or spotlight
current ranges. If this bit is set, the FL current sink can
be used to drive a flash of maximum duration 500ms and
the current range will be the high (flash) current range. If
this bit is cleared, the FL current sink can be used to drive
a continuous spotlight at a lower current and the current
range will be the lower (spotlight) current range, as shown
in Table 2.
LDO Control Register (0x03)
This register is used to enable the LDOs and to set their
output voltages.
101 through 111 are not used
OFF
LDO1_3
LDO1_2
LDO1_1
LDO1_0
LDO1
Output
Voltage
0
0
0
0
OFF
0
0
0
1
3.3V
0
0
1
0
3.2V
0
0
1
1
3.1V
0
1
0
0
3.0V
0
1
0
1
2.9V
0
1
1
0
2.8V
0
1
1
1
2.7V
1
0
0
0
2.6V
1
0
0
1
2.5V
1010 through 1111 are not used
OFF
20
SC621A
Serial Interface
The I2C General Specification
2
The SC621A is a read-write slave-mode I C device and
complies with the Philips I2C standard Version 2.1, dated
January 2000. The SC621A has four user-accessible
internal 8-bit registers. The I2C interface has been
designed for program flexibility, supporting direct format
for write operation. Read operations are supported on
both combined format and stop separated format. While
there is no auto increment/decrement capability in the
SC621A I2C logic, a tight software loop can be designed
to randomly access the next register independent of
which register you begin accessing. The start and stop
commands frame the data-packet and the repeat start
condition is allowed if necessary.
SC621A Limitations to the I2C Specifications
The SC621A only recognizes seven bit addressing. This
means that ten bit addressing and CBUS communication
are not compatible. The device can operate in either
standard mode (100kbit/s) or fast mode (400kbit/s).
Slave Address Assignment
The seven bit slave address is 0110 111x. The eighth bit is
the data direction bit. 0x6E is used for a write operation,
and 0x6F is used for a read operation.
Supported Formats
The supported formats are described in the following
subsections.
Direct Format — Write
The simplest format for an I2C write is direct format. After
the start condition [S], the slave address is sent, followed
by an eighth bit indicating a write. The SC621A I2C then
acknowledges that it is being addressed, and the master
responds with an 8 bit data byte consisting of the register
address. The slave acknowledges and the master sends
the appropriate 8 bit data byte. Once again the slave
acknowledges and the master terminates the transfer
with the stop condition [P].
Combined Format — Read
After the start condition [S], the slave address is sent,
followed by an eighth bit indicating a write. The SC621A
I2C then acknowledges that it is being addressed, and the
master responds with an 8 bit data byte consisting of the
register address. The slave acknowledges and the master
sends the repeated start condition [Sr]. Once again, the
slave address is sent, followed by an eighth bit indicating
a read. The slave responds with an acknowledge and the
previously addressed 8 bit data byte; the master then
sends a non-acknowledge (NACK). Finally, the master
terminates the transfer with the stop condition [P].
Stop Separated Reads
Stop-separated reads can also be used. This format
allows a master to set up the register address pointer for
a read and return to that slave at a later time to read the
data. In this format the slave address followed by a write
command are sent after a start [S] condition. The SC621A
then acknowledges it is being addressed, and the master
responds with the 8-bit register address. The master
sends a stop or restart condition and may then address
another slave. After performing other tasks, the master
can send a start or restart condition to the SC621A with
a read command. The device acknowledges this request
and returns the data from the register location that had
previously been set up.
21
SC621A
Serial Interface (continued)
I2C Direct Format Write
S
Slave Address
W
A
Register Address
S – Start Condition
W – Write = ‘0’
A – Acknowledge (sent by slave)
P – Stop condition
A
Data
A
P
Slave Address – 7-bit
Register address – 8-bit
Data – 8-bit
I2C Stop Separated Format Read
Master Addresses
other Slaves
Register Address Setup Access
S Slave Address W A Register Address A P S
S – Start Condition
W – Write = ‘0’
R – Read = ‘1’
A – Acknowledge (sent by slave)
NAK – Non-Acknowledge (sent by master)
Sr – Repeated Start condition
P – Stop condition
Slave Address B
Register Read Access
S/Sr
Slave Address
R A
Data
NACK P
Data
NACK P
Slave Address – 7-bit
Register address – 8-bit
Data – 8-bit
I2C Combined Format Read
S
Slave Address
W A
Register Address
S – Start Condition
W – Write = ‘0’
R – Read = ‘1’
A – Acknowledge (sent by slave)
NAK – Non-Acknowledge (sent by master)
Sr – Repeated Start condition
P – Stop condition
A Sr
Slave Address
R
A
Slave Address – 7-bit
Register address – 8-bit
Data – 8-bit
22
SC621A
Outline Drawing — MLPQ-UT-20 3x3
A
D
PIN 1
INDICATOR
(LASER MARK)
DIMENSIONS
INCHES
MILLIMETERS
DIM
MIN NOM MAX MIN NOM MAX
B
E
A2
A
SEATING
PLANE
aaa C
A
A1
A2
b
D
D1
E
E1
e
L
N
aaa
bbb
.020
.000
-
.024
.002
(.006)
.006 .008 .010
.114 .118 .122
.061 .067 .071
.114 .118 .122
.061 .067 .071
.016 BSC
.012 .016 .020
20
.003
.004
0.50
0.00
-
0.60
0.05
(0.1524)
0.15 0.20 0.25
2.90 3.00 3.10
1.55 1.70 1.80
2.90 3.00 3.10
1.55 1.70 1.80
0.40 BSC
0.30 0.40 0.50
20
0.08
0.10
C
A1
D1
e
LxN
E/2
E1
2
1
N
D/2
bxN
bbb
C A B
NOTES:
1.
CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
2. COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS THE TERMINALS .
3. DAP is 1.90 x 190mm.
23
SC621A
Land Pattern — MLPQ-UT-20 3x3
H
R
(C)
DIMENSIONS
K
G
Y
X
P
Z
DIM
INCHES
MILLIMETERS
C
G
H
K
P
R
X
Y
Z
(.114)
(2.90)
.083
.067
.067
.016
.004
.008
.031
.146
2.10
1.70
1.70
0.40
0.10
0.20
0.80
3.70
NOTES:
1.
CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
2.
THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY.
CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR
COMPANY'S MANUFACTURING GUIDELINES ARE MET.
3.
THERMAL VIAS IN THE LAND PATTERN OF THE EXPOSED PAD
SHALL BE CONNECTED TO A SYSTEM GROUND PLANE.
FAILURE TO DO SO MAY COMPROMISE THE THERMAL AND/OR
FUNCTIONAL PERFORMANCE OF THE DEVICE.
Contact Information
Semtech Corporation
Power Management Products Division
200 Flynn Road, Camarillo, CA 93012
Phone: (805) 498-2111 Fax: (805) 498-3804
www.semtech.com
24