AS3685A/AS3685B
Ultra Small High Efficiency 1000mA
Charge Pump for White LED Flash
General Description
The AS3685 is low noise high efficiency capacitive charge pump
with 1:1, 1:1.5 and 1:2 operating modes in a small 3x3mm DFN10
or a tiny 2x1.5mm WL-CSP (Wafer Level Chip Scale Package)
package. It can drive one flash LED at up to 1000mA current. It
supports flash/torch and indicator mode for the
flash LED.
Additionally the AS3685 limits the flash time automatically to
protect the flash LED.
Ordering Information and Content Guide appear at end of
datasheet.
Key Benefits & Features
The benefits and features of AS3685A/AS3685B, Ultra Small
High Efficiency 1000mA Charge Pump for White LED Flash are
listed below:
Figure 1:
Added Value Of Using AS3685A/AS3685B
Benefits
Features
• System safety
• High efficiency capactive charge pump with 1:1, 1:1.5
and 1:2 modes therefore maximum input current is
exactly controlled.
• Overtemperature protection
• Automatic 800ms flash timeout to protect the flash
LED
• Drive LED at high brightness for better pictures
• Up to 1000mA LED Current
• Flexible selection of interface type
• Two device variants:
• AS3685A: Direct control to select three currents
• AS3685B: Single pin interface or two pin
interface with strobe input; 17 different currents
can be selected
• Flexible package options
• DFN10 (3x3mm) 10 pins + exposed pad
• WL-CSP (2x1.5mm) 3x4 balls 0.5mm pitch
ams Datasheet
[v2-23] 2016-Mar-30
Page 1
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AS3685A/AS3685B − General Description
Applications
The AS3685A/AS3685B, Ultra Small High Efficiency 1000mA
Charge Pump for White LED Flash is ideal for Flash / Torch for
Mobile Phones, Digital Cameras and PDAs.
Figure 2:
Application Diagram of AS3685A/AS3685B
CFLY1 1.0 F
CFLY2 1.0 F
C1+ C1- C2+ C2VBAT
CBAT
2.2 F
VBAT
VCP
AS3685A
AS3685B
EN1
ILED
EN2
CVCP
2.2 F
DLED
ISET VSS
RTXMASK
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RISET
ams Datasheet
[v2-23] 2016-Mar-30
AS3685A/AS3685B − Pin Assignment
Pin Assignment
DFN10 (3x3mm)
Figure 3:
Pin Diagram DFN10 (3x3mm)
3
10
8
1
C1+ C1- C2+ C22
VCP
AS3685A
EN1 AS3685B
ILED
EN2
VBAT
5
7
4
9
ISET VSS
6
Exposed Pad
Figure 4:
Pin Description DFN10 (3x3mm)
Pin
Number
Pin
Name
Type
Description
1
C2-
AI/O
Flying Capacitor 2 connection – connect 1μF ceramic capacitor CFLY2
between C2- and C2+
2
VBAT
S
3
C1+
AI/O
Flying Capacitor 1 connection – connect 1μF ceramic capacitor CFLY1
between C1- and C1+
4
VCP
AI/O
Charge Pump Output voltage – connect flash LED anode to this pin
and add CVCP capacitor with 2.2μF to VSS
5
EN1
DI
6
ISET
AI/O
7
EN2
DI
ams Datasheet
[v2-23] 2016-Mar-30
Battery Supply Voltage
Digital Control Signal EN1
Current Generator input pin – connect current set resistor RISET
between this pin and VSS (and optional RTXMASK)
Digital Control Signal EN2
Page 3
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AS3685A/AS3685B − Pin Assignment
Pin
Number
Pin
Name
Type
Description
8
C2+
AI/O
Flying Capacitor 2 connection – connect 1μF ceramic capacitor CFLY2
between C2- and C2+
9
ILED
AI/O
Current Source input pin – connect flash LED cathode to this pin
10
C1-
AI/O
Flying capacitor 1 connection – connect 1μF ceramic capacitor CFLY1
between C1- and C1+
Exposed
Pad
VSS
S
Ground Connection – a proper thermal connection with several vias
to the ground plane is recommended
Note(s):
1. Pin Type Descriptions:
AI/O: Analog Pin
DI: Digital Input
S: Supply Pin
WL-CSP (2x1.5mm)
Figure 5:
WL-CSP (2x1.5mm) Pin Diagram
B1
D2
C2
D1
C1+ C1- C2+ C2C1
VBAT
VCP
B2
A1
AS3685A
EN1 AS3685B
ILED
EN2
C3
B3
ISET VSS
A3
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A2,D3
ams Datasheet
[v2-23] 2016-Mar-30
AS3685A/AS3685B − Pin Assignment
Figure 6:
Pin Description WL-CSP (2x1.5mm)
Pin
Number
Pin
Name
Type
A1
EN1
DI
Digital Control Signal EN1
A2
VSS
S
Ground Connection – a proper thermal connection to the ground
plane is recommended
A3
ISET
AI/O
Current Generator input pin – connect current set resistor RISET
between this pin and VSS (and optional RTXMASK)
B1
C1+
AI/O
Flying Capacitor 1 connection – connect 1μF ceramic capacitor
CFLY1 between C1- and C1+
B2
VCP
AI/O
Charge Pump Output voltage – connect flash LED anode to this pin
and add CVCP capacitor with 2.2μF to VSS
B3
EN2
DI
Digital Control Signal EN2
C1
VBAT
S
Battery Supply Voltage
C2
C2+
AI/O
Flying Capacitor 2 connection – connect 1μF ceramic capacitor
CFLY2 between C2- and C2+
C3
ILED
AI/O
Current Source input pin – connect flash LED cathode to this pin
D1
C2-
AI/O
Flying Capacitor 2 connection – connect 1μF ceramic capacitor
CFLY2 between C2- and C2+
D2
C1-
AI/O
Flying capacitor 1 connection – connect 1μF ceramic capacitor
CFLY1 between C1- and C1+
D3
VSS
S
Description
Ground Connection – a proper thermal connection to the ground
plane is recommended
Note(s):
1. Pin Type Descriptions WL-CSP (2x1.5mm):
AI/O: Analog Pin
DI: Digital Input
S: Supply Pin
ams Datasheet
[v2-23] 2016-Mar-30
Page 5
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AS3685A/AS3685B − Absolute Maximum Ratings
Absolute Maximum Ratings
Stresses beyond those listed in Absolute Maximum Ratings may
cause permanent damage to the device. These are stress ratings
only, and functional operation of the device at these or any
other conditions beyond those indicated in
Electrical Characteristics is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
Figure 7:
Absolute Maximum Ratings
Symbol
Parameter
Min
Max
Units
VBATMAX
Maximum Supply Voltage
-0.3
7.0
V
IIN
Input Pin Current without
causing latchup
-25
+25
mA
TSTRG
Storage Temperature Range
-55
125
°C
RHNC
Relative Humidity
(non-condensing)
5
85
%
ESDHBM
PT
PDERATE
Electrostatic Discharge
(Human Body Model)
±1000
Total Continuous Power
Dissipation
At 25°C, according to JEDEC 17
V
MIL 883 E Method 3015
1.14
W
DFN10 (3x3mm), TAMB = 70°C (1)
1.02
W
WL-CSP (2x1.5mm),
TAMB = 70°C (1)
16.3
mW/ °C
DFN10 (3x3mm)
14.7
mW/ °C
WL-CSP (2x1.5mm)
PT Derating Factor (2)
TJUNC
Junction Temperature
150
°C
TBODY
Body Temperature during
Soldering
260
°C
MSL
Comments
According to IPC/JEDEC
J-STD-020C
1
WLCSP package;
Represents a max. floor life time of
unlimited hours
3
DFN package;
Represents a max. floor life time of
168 hours
Moisture sensitivity level
Note(s):
1. Depending on actual PCB layout and PCB used; for peak power dissipation during flashing see document ‘AS3685 Thermal
Measurements’.
For 1A flash current see application notes ‘AN3685_1Aflash’ and ‘AN3685_1Aflash_thermal_1v0’.
2. The PT derating factor changes the total continuous power dissipation, if the ambient temperature is different to 70°C. Therefore
for e.g. 85°C calculate PT85°C = PT – P DERATE * (85°C to 70°C).
Page 6
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ams Datasheet
[v2-23] 2016-Mar-30
AS3685A/AS3685B − Electrical Characteristics
All limits are guaranteed. The parameters with minimum and
maximum values are guaranteed with production tests or SQC
(Statistical Quality Control) methods.
Electrical Characteristics
Figure 8:
Operating Conditions
Symbol
Parameter
Min
Typ
Max
Units
VBAT
Battery Supply Voltage
3.0
3.6
5.5
V
Supply voltage range
VBATFUNC
Battery Supply Voltage
(functionally working)
2.6
V
AS3685 functionally working, but
not all parameters fulfilled
0.4
A
Depending on load current and
charge pump mode
2.0
A
Limited lifetime, max 20,000s
25
85
°C
1.0
4.0
μA
EN1 = 0, EN2 = 0; VBAT ≤ 4.2V
0.85
mA
1:1 Mode
6.6
mA
1:1.5 Mode
8.1
mA
1:2 Mode
IBAT
Operating Current
TAMB
Ambient Temperature
IOFF
Off Mode Current
IOPERATING
Note
-30
Power Consumption
(without load)
Figure 9:
Charge Pump Characteristics
Symbol
Parameter
VCPOUT
V(VCP) Output
Voltage (without load
– do not short to VSS)
Min
Output Limitation
RCP
Eta
VRIPPLE
Charge Pump
Effective Resistance
Efficiency
Output Ripple
Voltage
ams Datasheet
[v2-23] 2016-Mar-30
Typ
Max
Units
VBAT x CPmode
V
Note
CP-mode is 1, 1.5 or 2
(automatically selected)
5.4
5.6
0.28
0.53
Ω
1:1 Mode
VBAT = 3.6V, ICPOUT = 200mA
1.37
2.00
Ω
1:1.5 Mode
VBAT = 3.3V, ICPOUT = 500mA,
TJUNCTION ≤ 85°C
1.95
2.44
Ω
1:2 Mode
VBAT = 3.0V, ICPOUT=700mA,
TJUNCTION ≤ 85°C
93
%
Vin=3.0V-4.5V, Iout=100mA
(charge pump alone)
mVpp
Vin=3.0-4.5V, Iout=350mA,
75
100
Internally limited
Page 7
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AS3685A/AS3685B − Electrical Characteristics
Symbol
Parameter
Min
Typ
Max
Units
fclk
Operating Frequency
-20%
1.0
+20%
MHz
tUP_DEB_LONG
Initial Mode
Switching Debounce
Time
tUP_DEB
Mode Switching
Debounce Time
Note
256
μs
Mode switching
up-debounce time after
enabling of the charge pump
or after mode switching
between 1:1 to 1:1.5
16
μs
Mode switching
up-debounce time in normal
operation
Figure 10:
Current Source (Sink) Characteristics
Symbol
ILED
IACCURACY
Parameter
Min
Output Current Range
Current Setting Accuracy
VISET
Current Generator Set
Point Voltage (pin ISET)
IISET
Current Generator
Operating Range
-10%
Typ
Max
Units
700
1000
mA
700mA: RISET = 14.2kΩ
1000mA: RISET = 10kΩ
500
+10%
mA
Measured with RISET = 19.9kΩ
and maximum flash current
1.3
10.0
130
IFLASH2ISET
Flash Current to Bias
Current Ratio
7650
ITORCH2ISET
Torch Current to Bias
Current Ratio
1639
VSWITCH
Mode Switching
Threshold on V(ILED)
between 1:1 → 1:1.5 and
1:1.5 → 1:2
Page 8
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V
400
150
200
250
μA
Note
IISET = VISET / RISET
if the resulting bias current is
higher than 200μA (typ.), the
current source is disabled
A/A
AS3685A, EN1=1, EN2=1 or
AS3685B at full flash current
(700mA with RISET = 14.2kΩ)
A/A
AS3685A, EN1=0, EN2=1
(150mA with RISET = 14.2kΩ)
mV
AS3685A, EN1=1, EN2=1 or
AS3685B with ILED>350mA
(with RISET = 14.2kΩ)
mV
All lower currents
ams Datasheet
[v2-23] 2016-Mar-30
AS3685A/AS3685B − Electrical Characteristics
Figure 11:
Digital Interface Characteristics
Symbol
Parameter
Min
VIH
High Level Input Voltage
VIL
ILEAKAGE
tPULSEWIDTH
Typ
Max
Units
1.5
VBAT
V
Low Level Input Voltage
0.0
0.5
V
Input Pin Leakage
Current
-10
10
μA
Pulsewidth for Signals on
EN1 and EN2 (high or low
pulses)
1.0
unlimited
μs
Note
For Pins EN1 and EN2
Do not leave EN1 and EN2
floating (47kΩ pulldowns
can be used)
Figure 12:
Protection Functions
Symbol
TOVTEMP
Parameter
Min
Overtemperature
Protection
TOVTEMPHYST
Overtemperature
Protection Hysteresis
tFLASHTIMEOUT
Flash Timeout Time
ams Datasheet
[v2-23] 2016-Mar-30
-20%
Typ
Max
Units
140
°C
5
°C
800
+20%
ms
Note
If the junction temperature
exceeds TOVTEMP , the current
sink will be disabled and the
charge pump switched back
into 1:1 mode until the
temperature drops below
TOVTEMP - TOVTEMPHYST
AS3685A, EN1=1, EN2=1 or
AS3685B flash modes
Page 9
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AS3685A/AS3685B − Typical Operating Characteristics
Typical Operating
Characteristics
Figure 13:
Efficiency vs. Battery Voltage (with Lumiled PWF1)
100
Efficiency of Charge Pump [%]
ILED=50m
ILED=100m
ILED=200m
ILED=300m
ILED=400m
90
ILED=500m
80
70
ILED=600m
60
ILED=700m
50
40
2.8
3.2
3.6
4.0
4.4
4.8
5.2
VBAT [V]
Figure 14:
Battery Current vs. Battery Voltage (with Lumiled PWF1)
1.6
1.4
1.2
IBAT [A]
1.0
0.8
ILED=700m
ILED=600m
0.6
ILED=500m
ILED=400m
ILED=300m
0.4
ILED=200m
0.2
ILED=50m
ILED=100m
0.0
2.8
3.2
3.6
4.0
4.4
4.8
5.2
VBAT [V]
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ams Datasheet
[v2-23] 2016-Mar-30
AS3685A/AS3685B − Typical Operating Characteristics
Figure 15:
LED Current I(ILED) vs. Battery Voltage (with Lumiled PWF1)
0.8
ILED=700m
0.7
ILED=600m
0.6
ILED=500m
ILED [A]
0.5
ILED=400m
0.4
ILED=300m
0.3
ILED=200m
0.2
ILED=100m
0.1
ILED=50m
0.0
2.8
3.2
3.6
4.0
4.4
4.8
5.2
VBAT [V]
Figure 16:
Linearity of Current Sink
0.8
ILED=700m
0.7
0.6
ILED=600m
ILED [A]
0.5
ILED=500m
ILED=400m
0.4
ILED=300m
0.3
ILED=200m
0.2
ILED=100m
0.1
ILED=50m
0.0
0.0
0.5
1.0
1.5
2.0
2.5
VILED [V]
ams Datasheet
[v2-23] 2016-Mar-30
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AS3685A/AS3685B − Typical Operating Characteristics
Figure 17:
I(ILED) vs. R(ISET) (Flash and Torch Mode of AS3685A)
1200
1000
Flash Mode
ILED [mA]
800
600
400
200
Torch Mode
0
0k
20k
40k
60k
80k
100k
120k
140k
R ISET [Ohm]
Figure 18:
Startup of AS3685A -- ILED Current
ILED 500mA/div 100μs/div
VBAT=3.3V, ILED=700mA
Page 12
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ams Datasheet
[v2-23] 2016-Mar-30
AS3685A/AS3685B − Typical Operating Characteristics
Figure 19:
Startup of AS3685A -- IBAT Current
IBAT 500mA/div 100μs/div
VBAT=3.3V, ILED=700mA
Figure 20:
Shutdown of AS3685A -- IBAT Current
IBAT 500mA/div 100μs/div
VBAT=3.3V, ILED=700mA
ams Datasheet
[v2-23] 2016-Mar-30
Page 13
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AS3685A/AS3685B − Typical Operating Characteristics
Figure 21:
Typical Operating Waveforms 1:1.5 Mode
VCP ac-coupled, 100mV/div 1μs/div
VBAT=3.3V, ILED=500mA
Figure 22:
Typical Operating Waveforms 1:2 Mode
VCP ac-coupled, 50mV/div 250ns/div
VBAT=3.3V, ILED=500mA
Page 14
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ams Datasheet
[v2-23] 2016-Mar-30
AS3685A/AS3685B − Detailed Description
Detailed Description
Figure 23:
Internal Circuit Diagram of AS3685A/AS3685B
C1+
VBAT
C1-
C2+
C2-
Low Noise
Charge Pump
1:1, 1:1.5, 1:2 Modes
VBAT
VCP
clk
mode
soft_limit
1MHz
5.3V
Overtemp
Detect
Vswitch
EN1
EN2
EN1
EN2
ILED
Digital
Control
1.3V
Different Control Logic
for AS3685A and AS3685B
TXMask
AS3685
ISET
VSS
Low Noise Charge Pump
The AS3685 charge pump uses two external flying capacitors
to generate output voltages higher than the battery voltage.
The charge pump can operate in three different modes:
• 1:1 Bypass Mode or Off Mode
• Battery input and output are connected by a
low-impedance switch
• Battery current = output current
• 1:1.5 Mode
• The output voltage is 1.5 times the battery voltage
(without load)
• Battery current = 1.5 times output current
• 1:2 Mode
• The output voltage is 2 times the battery voltage
(without load)
• Battery current = 2 times output current
The flying capacitors are switched at the fixed frequency fclk.
ams Datasheet
[v2-23] 2016-Mar-30
Page 15
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AS3685A/AS3685B − Detailed Description
Mode Switching
The AS3685 monitors the voltage at the current sink V(ILED) and
if this voltage falls below VSWITCH, for a time longer than the
debounce time, the charge pump automatically switches into
a higher mode. The debounce time is set to tUP_DEB_LONG at
enabling of the charge pump or immediately after a 1:1 to 1:1.5
mode change. Afterwards the debounce time is reduced to
t UP_DEB. (This allows the LED current to settle properly on
startup or after a mode change).
The charge pump enters always 1:1 mode in off mode or in case
of overtemperature. It is possible to avoid the 1:2 mode (factory
programmable) to limit the battery current to 1.5 times the
output (=LED) current.
Soft Start
The soft start mechanism reduces the inrush current. Battery
current is smoothed when switching the charge pump on and
also at each switching condition. This precaution reduces
electromagnetic radiation significantly.
Current Source (Sink)
The AS3685 operates in three different modes:
• Indicator Mode: A small (average) current is used to obtain
an indication function with the flash LED (e.g. indication
for camera operation).
• Torch Mode: A moderate current of e.g. 150mA allows the
use of the flash LED as a torch or video light.
• Flash Mode: A high current of e.g. 700mA (up to 1000mA)
is set for a high brightness flash. Only in this mode, the
flash timeout timer limits the total flash time.
• Pulsed Indicator Mode (only AS3685A): The control device
sends a short sequence to the AS3685A and the AS3685A
enables the flash LED for a defined fixed duration (torch
current setting). This duration is controlled by the
AS3685A and the control device does not need to start an
internal timer function.
The current through the LED and the operating mode is
controlled by the two digital pins EN1 and EN2. There are two
versions of the AS3685 available: AS3685A and AS3685B. The
only difference between these versions is the digital interface
as shown below:
Page 16
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ams Datasheet
[v2-23] 2016-Mar-30
AS3685A/AS3685B − Detailed Description
AS3685A Current Setting
For the AS3685A, the operating mode and the current through
the LED is defined by the following table:
Figure 24:
AS3685A Current Settings
EN1
0
EN2
0
ILED for RISET =
Mode
Percent of
Full Scale
ILED/IISET
14.2kΩ
10kΩ
Off
0mA
0mA
0%
0
(Off )
6.7mA average
(=214mA with 1/32
duty cycle (1))
0.67%
(=21.4% / 32)
52.2
(=ITORCH2ISET/32)
1
0
Indicator
4.7mA average
(=150mA with 1/32
duty cycle (1))
0
1
Torch
150mA
214mA
21.4%
1639
(=ITORCH2ISET )
1
1
Flash
700mA
1000mA
100%
7650
(=IFLASH2ISET )
Note(s):
1. The on-time for indicator mode is 1μs, off time 31μs (32μs = 32.25kHz).
Where I ISET is:
(EQ1)
V ISET
1.3V
I ISET = --------------- = --------------R ISET
R ISET
Application Hint: To obtain higher torch currents use the
following circuit:
Figure 25:
AS3685A Increasing Torch Current
VBAT
VBAT
AS3685A
EN1
EN1
EN2
EN2
ISET
RTORCH
RISET
ams Datasheet
[v2-23] 2016-Mar-30
Page 17
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AS3685A/AS3685B − Detailed Description
AS3685A Pulsed Indicator Mode
The torch mode is controlled by EN1=0 and EN2=1 as following
figure shows:
Figure 26:
AS3685A Torch Mode
EN1
EN2
ILED
Torch
Current
typ. 64μs
off
off
t
To allow an indication function using short pulses (with torch
current settings), the pulsed indicator mode can be used. The
control device sends a setup sequence (total time required: less
than 128μs) to ‘program’ the AS3685A, and the AS3685A
enables its current sink for the duration t TORCH (the current used
is exactly the torch current setting). Therefore the control does
not need to setup a timer to accurately define the duration of
the indicator pulse.
The duration t TORCH can be setup from 1ms to 15ms depending
on the number of pulses on EN2 as shown in the following figure
and table:
Figure 27:
AS3685A Pulsed Indicator Mode
Set duration of Torch-Pulse (tTORCH)
with number of pulses on pin EN2
EN1
EN2
max. 128μs
ILED
min tPULSEWIDTH
(1μs)
Torch
Current
typ. 64μs
off
Page 18
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tTORCH
off
t
ams Datasheet
[v2-23] 2016-Mar-30
AS3685A/AS3685B − Detailed Description
Figure 28:
AS3685A tTORCH Timings
ams Datasheet
[v2-23] 2016-Mar-30
H-L Pulses on EN2
tTORCH
1,2
0ms
ignored (noise filter)
3
1ms
4
2ms
5
3ms
6
4ms
7
5ms
8
6ms
9
7ms
10
8ms
11
9ms
12
10ms
13
11ms
14
12ms
15
13ms
16
14ms
≥17
15ms
Page 19
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AS3685A/AS3685B − Detailed Description
AS3685B Current Setting
The current through the LED (ILED) can be set in several steps
using the following waveforms:
Figure 29:
AS3685B Current Setting Method A
Define
Method A
Set current with
number of pulses
EN1
EN2
Current can be increased
if required
min.
tPULSEWIDTH
ILED
typ. 64μs
Flash/Strobe/Indicatior function
dependent on number of pulses
off
off
t
For method A, the current is started after a certain time after
the first rising edge of EN1. The AS3685B chooses method A, if
EN1 is high at the first rising edge of EN2.
Figure 30:
AS3685B Current Setting Method B
Define
Method B
Set current with
number of pulses
EN1
EN2
Current can be
increased if required
ILED
no time limit
off
min tPULSEWIDTH
typ. 64μs
Flash/Strobe/Indicatior function
dependent on number of pulses
off
t
For method B, the current is started after the second rising edge
of EN2. The AS3685B chooses method B, if EN1 is low at the first
rising edge of EN2.
Any high or low level duration for EN1 or EN2 should not be
shorter than t PULSEWIDTH.
The actual number of pulses on the pin EN1 (applies for
methods A and B) define the mode and the current settings for
the AS3685B:
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AS3685A/AS3685B − Detailed Description
Figure 31:
AS3685B Current Settings
H-L-H Pulses
on EN1
Mode
ILED
(for RISET =14.2kΩ)
ILED
(for RISET = 10kΩ)
ILED/IISET
EN1=EN2=0
Off
0mA
0%
0 (Off)
4.7mA average
6.7mA
1
(=150mA with 1/32 duty
cycle(1) )
(=214mA with 1/32
duty cycle(1) )
(=ITORCH2ISET/32)
2
41mA
60mA
448
85mA
120mA
929
4
129mA
180mA
1410
5
173mA
250mA
1891
217mA
310mA
2371
7
261mA
370mA
2852
8
305mA
440mA
3333
9
349mA
500mA
3814
10
393mA
560mA
4295
11
437mA
620mA
4776
481mA
690mA
5257
13
525mA
750mA
5737
14
569mA
810mA
6218
15
613mA
880mA
6699
16
657mA
940mA
7180
17
700mA
1000mA
7650 (=IFLASH2ISET )
0
Indicator
3
52.2
Torch
6
12
Flash
Flash
Note(s):
1. The on-time for indicator mode is 1μs, off time 31μs (32μs = 32.25kHz).
Where I ISET is:
(EQ2)
ams Datasheet
[v2-23] 2016-Mar-30
V ISET
1.3V
I ISET = --------------- = --------------R ISET
R ISET
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AS3685A/AS3685B − Detailed Description
AS3685B Single Wire Interface
Using the following application schematic, a single GPIO pin
can be used to control the mode and current of the AS3685B:
Figure 32:
AS3685B Single Wire Interface
Vbat
VBAT
AS3685B
EN1
EN1
EN2
CSINGLE
1nF
RSINGLE
single GPIO Pin to set
indicator/torch/flash mode
ISET
An example driving waveform can be (this uses method A as
shown above in section ‘AS3685B Current Settings’):
Figure 33:
AS3685B Example Single Wire Interface Driving Waveform
EN1
(EN2)
off
Set current with
number of pulses
Flash/Strobe/Indicatior function
dependent on number of previous pulses
off
The low time of the pulses on EN1 for setting the current should
be kept short. Then the (generated) signal on pin EN2 will stay
at a high level during this time ensuring correct operation.
R SINGLE should be chosen to fit to the actual driving waveform
on EN1.
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AS3685A/AS3685B − Detailed Description
AS3685B Two Wire Interface with Strobe Input
Using the following application schematic, the AS3685B current
and mode can be set accurately and the camera can directly
control the exact strobe time:
Figure 34:
AS3685B Two Wire Interface with Strobe Input
Vbat
VBAT
AS3685B
Two GPIO Pins to set
current and mode
EN1
EN1
EN2
EN2
ISET
STROBE
RSTROBE
Optional
Strobe Input
An example driving waveform can be (this uses method B as
shown above in section AS3685B Current Setting):
Figure 35:
AS3685B Example Two Wire Interface Driving Waveform
Enable/Disable current directly by the
camera module using the 'STROBE' input
EN1
EN2
STROBE
off
Set current with
number of pulses
Flash/Strobe/Indicatior function
dependent on number of previous pulses
GPIO output driving EN2 directly is
tristated and 'STROBE'
defines input EN2
ams Datasheet
[v2-23] 2016-Mar-30
off
GPIO output driving EN2
directly defines input EN2
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AS3685A/AS3685B − Detailed Description
AS3685A and AS3685B TXMask Function
If the battery has to supply two high currents at the same time
(e.g. the AS3685 flash and a RF-power amplifier) it is possible,
that the total current causes a high voltage drop on the battery
resulting in a shutdown of the complete system. In order to
avoid this shutdown, the AS3685 (AS3685A or AS3685B) can
reduce its current with the signal ‘TXMask’ using the following
circuit:
Figure 36:
TXMask Function of the AS3685
VBAT
VBAT
EN1
EN1
EN2
EN2
AS3685A
AS3685B
ISET
RTXMASK
TXMask
RISET
The TXMask signal is connected to e.g. the (RF-) power amplifier
enable pin (active high if the PA is enabled). This reduces the
flash current if the power amplifier is enabled and avoids the
unexpected shutdown of the system.
Note(s): The internal flash timeout timer (tFLASHTIMEOUT ) to limit
the total flash duration, is not affected by the TXMask function
(see also section Flash Timeout).
The I ISET current (current into the pin ISET) for TXMask = 0 can
be calculated with:
V ISET
V ISET
1.3V
1.3V
I ISET, TXMASK = 0 = --------------- + ------------------------- = --------------- + ------------------------R ISET R TXMASK
R ISET R TXMASK
(EQ3)
For TXMask = 1 the current IISET is reduced to:
(EQ4)
I
ISET, TXMASK = 1
V
– V ( TXMASK )
V
ISET
1.3V
1.3V – V ( TXMASK )
ISET
= ------------------ + ------------------------------------------------------------- = ------------------ + ------------------------------------------------------R
R
R
R
TXMASK
ISET
TXMASK
ISET
V(TXMask) is the actual voltage for the high level (‘1’) for the
signal TXMask
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AS3685A/AS3685B − Detailed Description
The maximum flash current ILEDMAX for TXMask=0 or 1 can be
calculated according to the following formula using the above
obtained I ISET values:
(EQ5)
I LEDMAX = I FLASH2BIAS I ISET = 7650 ⋅ I ISET
Choose the values for R ISET and RTXMASK according to your
application requirements.
Protection Functions
Overtemperature Protection
If the AS3685 junction temperature exceeds TOVTEMP , the
current sink will be disabled and the charge pump forced into
1:1 mode. If the junction temperature drops below TOVTEMP –
TOVTEMPHYST , the device enables the current sink again and the
charge pump resumes normal operation.
LED Shortcircuit Protection
If the LED is shorted (VCP to ILED), then depending on the set
current and the resulting high power dissipation inside the
AS3685, the overtemperature protection will trigger. This
protects the AS3685 and the system against damage. If the
AS3685 is in off-mode, then shorting of the diode will have no
influence on the system.
Note(s): Do not short VCP to VSS if the supply is not current
limited (e.g. by an internal protection inside the battery), as
there is an internal diode between VBAT (anode) and VCP
(cathode).
Flash Timeout
The flash duration of a single flash is limited automatically to
t FLASHTIMEOUT (applies only for ‘Flash’ mode(s)). This protects
the flash LED against thermal damage.
ams Datasheet
[v2-23] 2016-Mar-30
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AS3685A/AS3685B − Detailed Description
Layout Recommendations
To improve the heat dissipation, use a massive ground plane.
Figure 37:
AS3685 DFN10 (3x3mm) Layout Recommendation
CFLY1
CFLY2
AS3685
ILED
1
2
3
4
5
VBAT
EN1
CBAT
VSS
10
9
8
7
6
EN2
Top Layer
Bottom Layer
RISET
VIA, which is connected to
the ground plane, too
CVCP
Use ground place
connected to VSS
'Normal' VIA
VCP
Figure 38:
AS3685 WL-CSP (2x1.5mm) Layout Recommendation
Use ground plane
connected to VSS
CVCP
VCP
EN1
CBAT
VSS
VBAT
A1 A1
A2
A3
B1
B2
B3
C1 C2 C3
D1 D2 D3
CFLY2
RISET
EN2
ILED
AS3685
CFLY1
Top Layer
Inner Layer
Bottom Layer
VIA, which is connected to
the ground plane, too
'Normal' VIA
Micro VIA between
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AS3685A/AS3685B − External Components
External Components
Capacitor and Resistor Selection
Use low-ESR ceramic capacitors with X7R or X5R dielectric.
These capacitors allow good filtering and have a wide
temperature range. The connections of all external capacitors
should be kept as short as possible. All resistors should have a
tolerance of ±1%.
Usage of PCB Wire Inductance
The inductance between the battery and pin VBAT can be used
as a filter to reduce disturbance on the battery. Instead of using
one capacitor (C BAT ) it is recommended to split C BAT into C BAT1
and C BAT2 with the capacitance of
(EQ6)
C BAT1 = C BAT2 = C BAT
It is recommended to apply a minimum of 20nH (maximum
200nH) with low impedance. This inductance can be realized
on the PCB without any discrete coil. Assuming that a 1mm
signal line corresponds to approximately 1nH (valid if the
length (L) is significantly bigger than the width (W) of the line
(L/W
