General Description
The MAX8622 flyback switching regulator quickly and
efficiently charges high-voltage photoflash capacitors.
It is ideal for use in digital, film, cell-phone, and smart-
phone cameras that use either 2-cell alkaline/NiMH or
single-cell Li+ batteries. An internal, low-on-resistance
n-channel MOSFET improves efficiency by lowering
switch power loss.
A current-limited, continuous-mode, transformer-switch-
ing scheme quickly charges the output capacitor. The
cycle-by-cycle peak current-limit scheme has no inrush
current. Current limit is programmable to control the
maximum load drawn from the battery. An additional
input-voltage monitor loop extends battery life by
reducing the charge rate when the battery is nearly dis-
charged. This also permits the current limit to be set for
a faster charge rate under typical conditions, rather
than a level dictated by the worst-case discharge state
of the battery.
An open-drain DONE output indicates when the photo-
flash capacitor is completely charged. The MAX8622
automatically refreshes the output every 11s, efficiently
maintaining the capacitor charge level with minimum
battery drain.
The MAX8622 provides high charge accuracy by using
an external resistor-divider to monitor the output voltage.
Sensing directly at the transformer secondary prevents
output-capacitor discharge through feedback resistors
while still providing direct output sensing for optimum
voltage accuracy that is not transformer turns-ratio
dependent. The MAX8622 is offered in a 3mm x 3mm
10-pin TDFN package.
Applications
Digital Cameras
Cell-Phone Cameras
Film Cameras
Smartphone Cameras
Personal Media Players
Features
♦Charges Any Size Photoflash Capacitor
♦2.8s to Charge 100µF to 300V
♦No Inrush Current
♦High Accuracy Not Dependent on Transformer
Turns Ratio
♦Extends Battery Life with Input Voltage
Monitoring
♦Programmable Input Current Limit Up to 1.6A
♦Robust Architecture Allows Use of Low-Cost
Transformers
♦Automatic Refresh Mode
♦Charge-Done Indicator
♦Small, 3mm x 3mm, 10-Pin TDFN Package
MAX8622
Fast-Charge-Time Xenon Flash Charger for
Digital Still Cameras and Camera Phones
________________________________________________________________ Maxim Integrated Products 1
Ordering Information
19-3637; Rev 0; 4/05
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
EVALUATION KIT AVAILABLE
PART TEMP RANGE PIN-PACKAGE TOP
MARK
MAX8622ETB+ -40°C to +85°C10 TDFN 3mm x
3mm (T1033-1) APF
12345
109876
UVI
EN
SECGND
VCC
FB
ISET
TDFN 3mm × 3mm
TOP VIEW
LXPGND
MAX8622
DONE
Pin Configuration
MAX8622
VIN
1.5V TO 5.5V
VCC
2.5V TO 5.5V
1:15
SECVCC
DONE
EN
FB
PGND
GND
OUTPUT
300V
UVI ISET LX
Typical Operating Circuit
+Indicates lead-free packaging.
MAX8622
Fast-Charge-Time Xenon Flash Charger for
Digital Still Cameras and Camera Phones
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC = VEN = 3.3V, VFB = 0V, RISET = 75kΩ, VUVI = 1.5V, TA= -40°C to +85°C. Typical values are at TA= +25°C, unless otherwise
noted.) (Note 1)
Stresses beyond those listed under “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 the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
LX to PGND ............................................................-0.3V to +33V
DONE, VCC, UVI to GND..........................................-0.3V to +6V
FB, EN, ISET to GND..................................-0.3V to (VCC + 0.3V)
PGND to GND ...................................................... -0.3V to +0.3V
SEC Current................................................................... ±200mA
DONE Current...................................................................±25mA
Continuous Power Dissipation (TA= +70°C)
TDFN (derate 18.5mW/°C above +70°C)...................1481mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature Range ............................-40°C to +125°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
PARAMETER CONDITIONS MIN TYP MAX UNITS
VCC Voltage Range 2.5 5.5 V
VCC rising 2.180 2.300 2.425
VCC Undervoltage Threshold VCC falling 2.095 2.210 2.325 V
LX switching at 40kHz 1
LX switching at 300kHz 1.65 mA
VCC Supply Current
LX not switching, VCC = 5.5V 60 100 µA
TA = +25°C 0.1 1
VCC Shutdown Current VEN = 0V, VCC = 5.5V TA = +85°C 0.1 µA
VCC = 3.3V 0.31 0.5
LX On-Resistance ILX = 200mA VCC = 2.5V 0.35 0.6 Ω
TA = +25°C 0.1 1
LX Off-Leakage VLX = 5.5V, VEN = 0V TA = +85°C 0.1 µA
RISET = 200kΩ, TA = 0°C to +85°C 0.54 0.61 0.72
RISET = 75kΩ, TA = 0°C to +85°C 1.44 1.60 1.76LX Peak Current Limit
ISET = VCC, TA = 0°C to +85°C 1.44 1.60 1.76
A
Switching Frequency Circuit of Figure 2, output 90% of final value 300 kHz
SEC Sense Resistance 1.7 Ω
ISEC falling, RISET = 200kΩ10
ISEC falling, RISET = 75kΩ27
SEC Valley Current Threshold
ISEC falling, ISET = VCC 27
mA
TA = 0°C to +85°C 1.238 1.250 1.262
FB Trip Threshold VFB rising TA = -40°C to +85°C 1.231 1.250 1.269 V
TA = +25°C 0.1 1
FB Input Current VFB = 1.25V and EN = high,
or VEN = VFB = 0V TA = +85°C 0.1 µA
Output Refresh Rate From FB pulsed high to LX switching restarts 11 s
ISET Resistance Range Sets peak current limit from 0.6A to 1.6A 75 200 kΩ
VEN = VCC 1.0
ISET Voltage VEN = 0V 0 V
MAX8622
Fast-Charge-Time Xenon Flash Charger for
Digital Still Cameras and Camera Phones
_______________________________________________________________________________________ 3
Note 1: Limits are 100% production tested at TA= +25°C. Limits over the operating temperature range are guaranteed by design
and characterization.
ELECTRICAL CHARACTERISTICS (continued)
(VCC = VEN = 3.3V, VFB = 0V, RISET = 75kΩ, VUVI = 1.5V, TA= -40°C to +85°C. Typical values are at TA= +25°C, unless otherwise
noted.) (Note 1)
PARAMETER CONDITIONS MIN TYP MAX UNITS
TA = 0°C to +85°C 1.96 2.00 2.04
UVI Trip Threshold Falling External 25kΩ resistor in series
with UVI TA = -40°C to +85°C 1.94 2.00 2.06 V
TA = 0°C to +85°C 2.10 2.14 2.18
UVI Trip Threshold Rising External 25kΩ resistor in series
with UVI TA = -40°C to +85°C 2.08 2.14 2.20 V
UVI Pulldown Resistance 25 kΩ
TA = +25°C 0.1 1
UVI Input Current VEN = 0V, VUVI = VCC = 5.5V TA = +85°C 0.1 µA
VIH 0.4
EN Input Voltage When charging starts/stops VIL 1.4 V
TA = +25°C 0.1 1
EN Input Leakage Current VEN = 0 to 5.5V TA = +85°C 0.1 µA
DONE Output-Voltage Low IDONE = 5mA 40 150 mV
TA = +25°C 0.1 1
DONE Output-Current High VDONE = 5.5V TA = +85°C 0.1 µA
MAX8622
Fast-Charge-Time Xenon Flash Charger for
Digital Still Cameras and Camera Phones
4 _______________________________________________________________________________________
Typical Operating Characteristics
(VCC = VIN = VEN = 3.5V, circuit of Figure 2, TA= +25°C, unless otherwise noted.)
CHARGE TIME (FROM 30V TO 300V)
vs. INPUT VOLTAGE (1.6A PEAK)
MAX8622 toc01
INPUT VOLTAGE (V)
CHARGE TIME (s)
4.53.5
1
2
3
4
5
6
7
8
0
2.5 5.5
ISET = VCC
100µF150µF
50µF
CHARGE TIME (FROM 30V TO 300V)
vs. INPUT VOLTAGE (800mA PEAK)
MAX8622 toc02
5
10
15
20
25
0
INPUT VOLTAGE (V)
CHARGE TIME (s)
4.53.52.5 5.5
RISET = 150kΩ
50µF
100µF
150µF
EFFICIENCY vs. OUTPUT VOLTAGE
MAX8622 toc03
OUTPUT VOLTAGE (V)
EFFICIENCY (%)
20010050 150 250
10
20
30
40
50
60
70
80
90
0
0 300
VIN = 5V
VIN = 3.5V
COUT = 150µF
280
300
290
320
310
330
340
2.7 4.13.4 4.8 5.5
INPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE VS. INPUT VOLTAGE
MAX8622 toc04
OUTPUT VOLTAGE vs. TEMPERATURE
MAX8622 toc05
TEMPERATURE (°C)
OUTPUT VOLTAGE (V)
6035-15 10
290
295
300
310
305
315
320
-40 85
VIN = 3.5V AND 5V
PRIMARY CURRENT LIMIT
vs. ISET RESISTOR
MAX8622 toc06
ISET RESISTOR (kΩ)
PRIMARY CURRENT LIMIT (A)
17515012510075
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
0.0
50 200
PRIMARY CURRENT LIMIT
vs. TEMPERATURE
MAX8622 toc07
TEMPERATURE (°C)
PRIMARY CURRENT LIMIT (A)
6035-15 10
1.40
1.45
1.50
1.55
1.65
1.60
1.70
1.75
1.35
-40 85
ISET = VCC
PEAK PRIMARY CURRENT
vs. INPUT VOLTAGE
MAX8622 toc08
INPUT VOLTAGE (V)
PEAK PRIMARY CURRENT (A)
4.83.4 4.1
0.6
0.8
1.0
1.2
1.6
1.4
1.8
2.0
0.4
0.2
0.0
2.7 5.5
QUIESCENT CURRENT vs. INPUT
VOLTAGE AFTER CHARGE COMPLETE
MAX8622 toc09
QUIESCENT CURRENT (µA)
20
40
60
80
100
120
140
160
180
200
0
INPUT VOLTAGE (V)
4.53.52.5 5.5
RISET = 75kΩ
MAX8622
Fast-Charge-Time Xenon Flash Charger for
Digital Still Cameras and Camera Phones
_______________________________________________________________________________________ 5
Typical Operating Characteristics (continued)
(VCC = VIN = VEN = 3.5V, circuit of Figure 2, TA= +25°C, unless otherwise noted.)
SWITCHING WAVEFORMS
MAX8622 toc10
1µs/div
ISEC
IPRI
VLX
100mA/div
0
1A/div
0
10V/div
0
VOUT = 100V
LINE STEP THROUGH UVI
MAX8622 toc11
20µs/div
IPRI
VIN 500mV/div
1A/div
0
VIN = 2.4V TO 2.0V TO 2.4V, VCC = 3.5V,
VOUT = 100V, RUVI = 25kΩ
CHARGE PROFILE
MAX8622 toc12
1s/div
VLX
VOUT
VDONE
VEN
0
0
10V/div
100V/div
5V/div
5V/div
C3 = 150µF
Pin Description
MAX8622
Detailed Description
The MAX8622 charges photoflash capacitors quickly
and efficiently. It employs a transformer flyback DC-DC
conversion topology and includes a 0.31Ωinternal
power switch. Figure 1 shows the functional diagram.
Control Scheme
The MAX8622 uses a constant peak and valley current
control scheme to precisely control the photoflash
capacitor charging current. A resistor at ISET and the
transformer turns ratio sets the charge current.
Pulling EN high initiates charging. LX turns on and the
current in the transformer primary winding rises to a
peak current between 0.6A and 1.6A, depending on
the ISET resistor (1.6A if ISET is connected to VCC). LX
then turns off, and current is delivered to the photoflash
capacitor by the transformer secondary and rectifying
diode. As secondary current ramps down, it is moni-
tored through the SEC pin. When this current drops to
1.67% (with a 1:15 transformer turns ratio) of the peak
current limit, the LX switch turns on and a new charge
cycle begins. This cycle repeats itself, adding power to
the photoflash capacitor until the target output voltage
is reached.
Switching frequency is determined by the time required
to ramp the primary-side inductance to the LX current
limit and the discharge rate of the secondary current.
The switching frequency changes as the output capaci-
tor charges to the target output voltage. Once the tar-
get output voltage is reached, the MAX8622
automatically refreshes the output every 11s, efficiently
maintaining the capacitor charge level with minimum
battery drain. The MAX8622 draws only 60µA (typ) in
automatic refresh mode. Automatic refresh can be
overridden by pulling EN low.
Secondary Side Sensing
Output regulation is accomplished using a resistor-
divider connected to the anode of the output rectifying
diode (see Figure 2). This connection eliminates DC
current drain on the output capacitor while still provid-
ing direct output sensing for optimum voltage accuracy
that is not dependent on transformer turns ratio. The
MAX8622 samples FB during the flyback phase (when
LX is off). When FB rises above 1.25V, charging stops
and DONE pulls low. If EN remains high, autorefresh
then occurs every 11s. See the Adjustable Output
Voltage section for information on selecting values for
the resistor-divider.
Fast-Charge-Time Xenon Flash Charger for
Digital Still Cameras and Camera Phones
6 _______________________________________________________________________________________
S
REF
1.5V TO 5.5V
REF
VCC
VIN
2.5V TO 5.5V VCC
VOUT
ISET
R6
R5 UVI
EN
DONE
R
QB
Q
MAX8622
REF
SEC
PGND
LX
T1
R1
R3
D1
C3
300V
VCC
FB
GND
R
S
Q
S
R
Q
0.1µs
11s
TTL
20µs
Figure 1. Functional Diagram
Extending Battery Life with UVI
The UVI circuit allows the output to charge as fast as
possible without causing the input voltage to drop
below the selected voltage level. This allows a camera
to be ready to flash in a short time when the battery is
fresh, while still charging the photoflash capacitor when
the battery is at low capacity by extending charge time
and limiting battery drain.
The UVI comparator determines if the input source is
being pulled low as a result of the input current drawn
by photoflash charging or some other process in the
camera. When UVI drops below the UVI falling thresh-
old, the LX control latch is reset and the internal
MOSFET is immediately turned off. The LX switch
remains off until the current in the transformer sec-
ondary drops to the valley trip threshold, or for 1µs,
whichever is longer. The LX switch turns on only if the
input is above the UVI rising threshold. This lowers the
average charge current.
Applications Information
Transformer Design
The transformer is a key element in any transformer fly-
back design. The switching elements in this topology
are subject to significantly large voltage and current
stresses, depending on the transformer design. The
transformer also plays a key role in the noise perfor-
mance of the circuit. Proper selection, design, and con-
struction of the transformer are crucial to the
performance of a photoflash charger. Recommended
transformers and their key parameters are listed in
Table 1.
Transformer Turns Ratio
The transformer turns ratio should be high enough so
that the transformer’s peak primary voltage does not
exceed the voltage rating (33V) of the internal MOSFET.
The turns ratio is given by:
where VD1 is the forward voltage of D1.
If the target voltage for the photoflash capacitor is
300V, this implies a turns ratio of greater than 1:10 at a
minimum input voltage of 1.8V. A transformer with a
turns ratio of 1:15 is typically recommended for appli-
cations using the MAX8622.
Primary Inductance
The MAX8622 operates either in discontinuous-conduc-
tion mode (DCM) or in continuous-conduction mode
(CCM). Generally, CCM operation offers higher efficien-
NVV
V
OUT MAX D
IN
≥+
−
() 1
33
MAX8622
Fast-Charge-Time Xenon Flash Charger for
Digital Still Cameras and Camera Phones
_______________________________________________________________________________________ 7
MAX8622
C2
10µF
C1
1µF
VIN
1.5V TO 5.5V
VCC
2.5V TO 5.5V
1:15
SECVCC
DONE
EN
FB
ISET
PGND
GND
T1
R4
100kΩ
R2
124kΩ
R1
124kΩ
C3
150µF
D1
OUTPUT
300V
R3
1kΩ
UVI LX
Figure 2. MAX8622 Typical Application Circuit with Default 1.6A Primary Current Limit
DC RESISTANCE (Ω)
TRANSFORMER TURNS RATIO
(SEC/PRI)
PRIMARY
INDUCTANCE (µH) CAPACITANCE (pF) PRI SEC
TDK LDT565630T-011 15 6 30 0.11 15
Tokyo Coil TTRN-038S-017-T 15 6.4 11 0.11 24
Tokyo Coil TTRN-SU20S-001-T 15 6.5 4 0.31 44
Table 1. Transformer Design Parameters
MAX8622
cy and lower ripple currents for the same output power
as compared to DCM operation. The capacitive switch-
ing losses in the switch are minimal at the boundary of
DCM and CCM operation. The primary inductance for
the transformer is therefore estimated based on the
assumption that the MAX8622 is operating close to this
boundary for highest efficiency and minimum charge
time.
The MAX8622 has an on-time limit (tON(MAX)) of typical-
ly 25µs. Assuming the default current limit (ILIMIT) of
1.6A, the maximum value of primary inductance for a
1.8V minimum input and a 1.6A primary current limit is
given by:
The boundary of DCM/CCM operation is determined by
monitoring the secondary valley current. The secondary
current-sensing circuit in the MAX8622 has a blanking
time of about 150ns. This implies a minimum off-time
tOFF(MIN) of 250ns for the MAX8622 to have adequate
time to sense the secondary valley current. Since the
minimum discharge time occurs at the target output
voltage VOUT(MAX), the minimum secondary induc-
tance LSEC(MIN) is given by:
where N is the transformer turns ratio. This in turn implies
a minimum primary inductance LPRI(MIN) given by:
For a typical turns ratio of 15 (see the Transformer Turns
Ratio section), the LPRI(MIN) is calculated to be 3µH.
Choose a value between LPRI(MIN) and LPRI(MAX)
based on other considerations for the leakage induc-
tance and the transformer capacitance. A transformer
with a primary inductance of 6µH is recommended for
most applications.
Leakage Inductance
A particularly important transformer parameter is leak-
age inductance. In a practical transformer construction,
all windings cannot be equally well-coupled to the core
because of physical separation. If the primary induc-
tance is high, the transformer may need multiple wind-
ings for the primary. A small amount of energy is stored
between the windings and this energy is represented
as leakage inductance. If the primary inductance is too
small, the primary windings may not cover the width of
the core and result in poor coupling to the secondary.
This also increases the leakage inductance.
Leakage inductance does not participate in the primary
to secondary energy transfer. Since the leakage induc-
tance does not find a path for the current built up dur-
ing the switch on-time, it results in voltage spikes and
ringing at the drain of the MAX8622 power switch (LX),
when it turns off. The MAX8622 internal switch is
designed to be robust to withstand these voltage
spikes; however, voltage overshoot should be mini-
mized because it reduces total efficiency. Leakage
inductance also delays the transfer of power from input
to output causing an increase in charge time.
In addition, transformer secondary leakage inductance
may couple with the reverse recovery current of the
output rectifier diode to cause ringing when the diode
turns off. The transformer secondary leakage induc-
tance and the capacitance of the rectifier determine
this resonant frequency. There is typically very little loss
in the resonant circuit, so this network can generate
many cycles of ringing after the spike. The ringing can
therefore affect the peak primary current-sense signal
used by the MAX8622. The transformer secondary
leakage inductance is a function of the primary leakage
inductance.
Care should be taken during transformer design while
using techniques such as sandwiching the secondary
between two primary windings to minimize leakage
inductance. This can cause high winding-to-winding
capacitance, reduce the efficiency of the circuit, and
increase the charge time.
Transformer Secondary Capacitance
The total capacitance of the secondary should be mini-
mized for both efficient and proper operation. Since the
secondary of the transformer undergoes large voltage
swings, capacitance on the secondary is a significant
detriment to efficiency. This capacitance is reflected on
the primary as an effective capacitance proportional to
the square of the transformer turns ratio. It therefore
dominates the resulting capacitance on the primary.
LVt
IN N
H
N
PRI MIN OUT MAX OFF MIN
LIMIT
() () ()
.
=×
×=××
×=
−
300 250 10
16
47
9µ
LVt
IN
SEC MIN OUT MAX OFF MIN
LIMIT
() () ()
/
=×
LVt
IH
PRI MAX IN MIN ON MAX
LIMIT
() () ( ) .
.
=×=×× =
−
1 8 25 10
16 28
6µ
Fast-Charge-Time Xenon Flash Charger for
Digital Still Cameras and Camera Phones
8 _______________________________________________________________________________________
Both the leakage inductance and the secondary
capacitance of the transformer should be minimized for
efficient operation.
Rectifying Diode
The rectifying diode(s) must have sufficient reverse
voltage and forward-current ratings. The peak reverse
voltage VR(PEAK) seen by the diode(s) is given by:
is the same as the secondary peak current ISBC(PEAK).
The peak current of the diode ISEC(PEAK) is determined
by the peak primary current as:
Rectifier capacitance and transformer secondary leak-
age inductance couple to cause ringing when the
diode turns off. The overshoot caused by this ringing
may exceed the diode voltage rating and cause dam-
age to the diode. The ringing can also affect the cur-
rent-sense signal in the MAX8622. The rectifying diode
should therefore have very low capacitance; 5pF or
less is recommended.
The transition from the conduction to the blocking state
in the diode takes a finite time, known as the reverse
recovery time (trr). An ideal diode would have no
reverse leakage current at any time. In a real diode,
reverse leakage current flows from cathode to anode for
a short period of time during reverse recovery to remove
the injected carriers before the voltage can be blocked.
The reverse recovery time should be as small as possi-
ble to reduce losses due to this reverse current. The
reverse recovery waveforms also generate noise that
may interfere with the current-sense signal. The slope of
the waveform for recovery from the peak reverse current
to 0A is used to characterize the diode as a soft recov-
ery type if the slope is small, or a hard recovery type if
the slope is steep. A soft recovery diode exhibits signifi-
cantly lower switching noise than a hard recovery type.
Snubbers can be used to make the reverse recovery
waveform soft, but they also lower efficiency. A diode
with a small trr and soft recovery is definitely an advan-
tage. Recommended diodes are listed in Table 2.
Capacitor Selection
The VCC and VIN decoupling capacitors should be mul-
tilayer ceramic type with X5R or X7R dielectric for use
across a wide temperature range. Use of Y5V and Z5U
dielectrics is strongly discouraged due to the higher
voltage and temperature coefficient of these materials.
Adjustable Output Voltage
The MAX8622 uses secondary feedback to sense the
output voltage (see Figure 2). The output voltage is set
by the ratio of a resistor voltage-divider. Choose the
lower resistor (R3 in Figure 2), connected from FB to
GND, less than 2kΩ. A typical value for R3 is 1kΩ.
Larger resistor values combined with parasitic capaci-
tance at FB can slow the rise time of the FB voltage
during each cycle. This could prevent the MAX8622
from detecting when the output has reached the
desired level.
The value for the upper resistor (R1 and R2 in Figure 2)
is found from:
where VFB is 1.25V. Make sure the voltage rating of the
resistors is sufficient. It is often necessary to use two
resistors in series for the upper resistor to meet the
resistor voltage rating.
Choosing a Resistor for
Lowering Charge Current
The peak primary current limit for the MAX8622 is set to
the default value of 1.6A by connecting ISET to VCC.
This current limit works well for most applications. If a
lower current limit is needed, connect a resistor (R6 in
Figure 3) from ISET to GND. Select R6 as follows:
RA
Ik
LIMIT
616 75=×
.Ω
RRRR
V
V
UPPER OUT
FB
=+ = −
⎛
⎝
⎜⎞
⎠
⎟
12 3 1
II
N
SEC PEAK LIMIT
()
=
VV NV
R PEAK OUT MAX IN() ()
=+×
()
MAX8622
Fast-Charge-Time Xenon Flash Charger for
Digital Still Cameras and Camera Phones
_______________________________________________________________________________________ 9
PART NUMBER SUPPLIER
MAXIMUM
REVERSE
VOLTAGE
(V, EACH)
CAPACITANCE
(pF, EACH)
BAV23S (dual) Phillips 250 5
BAW101S (dual) Phillips 300 2
CMPD2004S
(dual) Central 240 5
Table 2. Recommended Diodes
MAX8622
Adjusting Battery Threshold for
Lowering Charge Current
The UVI circuit allows a camera to be ready to flash in a
short time when the battery is fresh, while still allowing
flash pictures when the battery is at low capacity by
extending the charge time to limit the battery drain. The
MAX8622 does this by turning off the internal switch
when the battery voltage dips below the set threshold.
Set the UVI falling threshold by connecting a resistor
(R5 in Figure 3) between UVI and the battery input,
which forms a voltage-divider with an internal 25kΩ
resistor. Select the UVI resistor value as follows:
where VUVI is 1V and VIN(MIN) is the desired minimum-
operating battery voltage.
When VCC is connected to VIN, the UVI falling
threshold must be set to 2.5V or higher.
DONE
Output
DONE is an open-drain output that pulls low when EN is
high and the circuit has finished charging the output
capacitor. Once the output capacitor is initially
charged, DONE remains low until EN or VCC goes low.
To use DONE as a logic-level output, connect a pullup
resistor (typically 100kΩ) from DONE to the logic sup-
ply rail. DONE can also directly drive an LED (connect-
ed as shown in Figure 3). When driving an LED, select
the series resistor value so the current into DONE is
less than 10mA. Note that in the DONE state, the
MAX8622 autorefreshes every 11s as long as EN is
high.
Layout Guidelines
The high-voltage operation of this application demands
careful attention to board layout. Larger than minimum
space between traces in the high-voltage area are rec-
ommended. This is essential to meet the breakdown
specifications of the board. To minimize the high-fre-
quency noise generated by switching, high dv/dt paths
must be made as short as possible. Shortening high
dv/dt paths reduces the size of antennas that radiate
noise. A high di/dt loop creates noise due to radiated
magnetic fields. To reduce high di/dt loop-generated
noise, the loop needs to be made as small as possible.
Keep the area for the high-voltage end of the secondary
as small as possible. Refer to the MAX8622 evaluation
kit data sheet for a layout example.
Warning: Lethal voltages are present in this circuit.
Use caution when working with this circuit.
Chip Information
TRANSISTOR COUNT: 6062
PROCESS: BiCMOS
Rk
V
V
IN MIN
UVI
525 1=× −
⎛
⎝
⎜⎞
⎠
⎟
Ω()
Fast-Charge-Time Xenon Flash Charger for
Digital Still Cameras and Camera Phones
10 ______________________________________________________________________________________
MAX8622
VIN
1.5V TO 5.5V
VCC
2.5V TO 5.5V
1:15
T1
SECVCC
DONE
EN
FB
PGND
GND
UVI
ISET
LX
R6
120kΩ
R2
124kΩ
R1
124kΩ
R3
1kΩ
R4
330kΩ
R5
25kΩ
D1
D2
OUTPUT
300V
C3
150µF
C1
1µF
C2
10µF
Figure 3. MAX8622 Typical Application Circuit with Resistor-Set Primary Current Limit Set by R6
MAX8622
Fast-Charge-Time Xenon Flash Charger for
Digital Still Cameras and Camera Phones
______________________________________________________________________________________ 11
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
6, 8, &10L, DFN THIN.EPS
L
CL
C
PIN 1
INDEX
AREA
D
E
L
e
L
A
e
E2
N
G
1
2
21-0137
PACKAGE OUTLINE, 6,8,10 & 14L,
TDFN, EXPOSED PAD, 3x3x0.80 mm
-DRAWING NOT TO SCALE-
k
e
[(N/2)-1] x e
REF.
PIN 1 ID
0.35x0.35
DETAIL A
b
D2
A2
A1
MAX8622
Fast-Charge-Time Xenon Flash Charger for
Digital Still Cameras and Camera Phones
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2005 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
COMMON DIMENSIONS
SYMBOL MIN. MAX.
A0.70 0.80
D2.90 3.10
E2.90 3.10
A1 0.00 0.05
L0.20 0.40
PKG. CODE ND2 E2 eJEDEC SPEC b[(N/2)-1] x e
PACKAGE VARIATIONS
0.25 MIN.k
A2 0.20 REF.
2.30±0.101.50±0.106T633-1 0.95 BSC MO229 / WEEA 1.90 REF0.40±0.05
1.95 REF0.30±0.05
0.65 BSC
2.30±0.108T833-1
2.00 REF0.25±0.05
0.50 BSC
2.30±0.1010T1033-1
2.40 REF0.20±0.05- - - -
0.40 BSC
1.70±0.10 2.30±0.1014T1433-1
1.50±0.10
1.50±0.10
MO229 / WEEC
MO229 / WEED-3
0.40 BSC - - - - 0.20±0.05 2.40 REFT1433-2 14 2.30±0.101.70±0.10
T633-2 6 1.50±0.10 2.30±0.10 0.95 BSC MO229 / WEEA 0.40±0.05 1.90 REF
T833-2 8 1.50±0.10 2.30±0.10 0.65 BSC MO229 / WEEC 0.30±0.05 1.95 REF
T833-3 8 1.50±0.10 2.30±0.10 0.65 BSC MO229 / WEEC 0.30±0.05 1.95 REF
-DRAWING NOT TO SCALE-
G2
2
21-0137
PACKAGE OUTLINE, 6,8,10 & 14L,
TDFN, EXPOSED PAD, 3x3x0.80 mm
DOWNBONDS
ALLOWED
NO
NO
NO
NO
YES
NO
YES
NO