AMS AMS1072

AMS1072
DESCRIPTION
FEATURES
The AMS1072 is a step-up converter designed for
driving up to 39 white LEDs (13 strings of 3 LEDs
each) from a 5V system rail. The AMS1072 uses a
current mode, fixed frequency architecture to
regulate the LED current, which is measured
through an external current sense resistor. Its low
104mV feedback voltage reduces power loss and
improves efficiency. The OV pin monitors the
output voltage and turns off the converter if an
over-voltage condition is present due to an open
circuit condition.
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The AMS1072 includes under-voltage lockout,
current limiting and thermal overload protection
preventing damage in the event of an output
overload.
2.5V to 8V Input Voltage Range
On Board Power MOSFET
Drives up to 39 White LEDs at 5V Input
Up to 92% Efficiency
1.3MHz Fixed Switching Frequency
Open Load Shutdown
Low 104mV Feedback Voltage
Soft-Start/PWM Dimming
UVLO, Thermal Shutdown
Internal 1.3A Current Limit
Available in SOT23-6 Packages
APPLICATIONS
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The AMS1072 is available in small 6-pin SOT23-6
packages.
Cell Phones
Handheld Computers and PDAs
Digital Still Cameras
Small LCD Displays
TYPICAL APPLICATION
VIN
4V - 6V
13 Strings
IN
EN
EN
SW
AMS1072
GND
OV
FB
1
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AMS1072
PACKAGE REFERENCE
TOP VIEW
SW
1
6
IN
GND
2
5
OV
FB
3
4
EN
Part Number
Package
Temperature
AMS1072
SOT23-6
–40°C to +85°C
ABSOLUTE MAXIMUM RATINGS
SW Pin......................................–0.5V to +28.5V
All Other Pins ..............................–0.3V to +8V
Storage Temperature.............. –65°C to +150°C
Recommended Operating Conditions
IN Supply Voltage ..............................2.5V to 8V
Output Voltage ....................................VIN to 25V
Operating Temperature............. –40°C to +85°C
ELECTRICAL CHARACTERISTICS
VIN = VEN = 5V, TA = +25°C, unless otherwise noted.
Parameters
Symbol Condition
Operating Input Voltage
Supply Current (Shutdown)
Supply Current (Quiescent)
Switching Frequency
Maximum Duty Cycle
Under Voltage Lockout
IN Under Voltage Lockout
Under Voltage Lockout
Hysteresis
Open Lamp Shutdown
Threshold
Min
VIN
2.5
VEN = 0V
VFB = 0.15V
VOV
Max
Units
8
1
750
1.5
V
µA
µA
MHz
%
VFB = 0V
1.0
85
0.1
690
1.3
92
VIN Rising
2.25
2.45
V
92
mV
28
V
fSW
UVLO
Typ
V OV Rising
2
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ELECTRICAL CHARACTERISTICS (continued)
AMS1072
VIN = VEN = 5V, TA = +25°C, unless otherwise noted.
Parameters
Symbol Condition
Enable
EN Threshold
EN Threshold
EN Hysteresis
EN Input Bias Current
Feedback
FB Voltage
FB Input Bias Current
Output Switch
SW On-Resistance
SW Current Limit
VEN Rising, VIN = 5V
VEN Rising, VIN = 2.5V
Min
Typ
Max
Units
1.1
0.8
1.35
1.6
V
V
mV
µA
114
mV
nA
90
1
VEN = 0V, 5V
94
–600
VFB = 0.1V
R
ON
Duty Cycle = 60%
Thermal Shutdown
104
–300
0.5
1.33
Ω
A
160
°C
PIN FUNCTIONS
SOT23-6
Pin #
Name Description
1
SW
2
GND
3
FB
4
EN
5
OV
6
IN
Power Switch Output. SW is the drain of the internal MOSFET switch. Connect
the power inductor and output rectifier to SW.
Ground.
Feedback Input. The AMS1072 regulates the voltage across the current sense
resistor between FB and GND. Connect a current sense resistor from the bottom
of the LED string to GND. Connect the bottom of the LED string to FB. The
regulation voltage is 104mV.
Regulator On/Off Control Input. A high input at EN turns on the converter, and a
low input turns it off. When not used, connect EN to the input source for automatic
startup. The EN pin cannot be left floating.
Over Voltage Input. OV measures the output voltage for open circuit protection.
Connect OV to the output at the top of the LED string.
Input Supply Pin. Must be locally bypassed.
3
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AMS1072
Functional Block Diagram
FB
+
-
CONTROL
LOGIC
+
AMPLIFIER
M1
SW
PWM
COMPARATOR
104mV
+
+
CURRENT
SENSE
AMPLIFIER
1.3MHz
OSC
APPLICATION INFORMATION
VIN
4V to 6V
MBR0520
IN
EN
9 Strings
Total
SW
AMS1072
GND
OV
FB
ILED = 104mV ×
R1 + R2
R1 × R2
4
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GND
AMS1072
Dimming Control
VDC
LED1
LED2
LED3
AMS1072
FB
Dimming Control Using a DC Voltage
LED1
LED1
AMS1072
LED2
PWM
EN
FB
LED3
LED3
AMS1072
LED2
PWM
FB
1KHz or below
PWM signal is above 1KHz
Dimming Control Using a Logic Signal
Dimming Control Using a Filtered PWM Signal
5
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AMS1072
PACKAGE INFORMATION
SOT23-6
0.95
BSC
0.60
TYP
2.80
3.00
6
4
1.20
TYP
1.50
1.70
1
2.60
TYP
2.60
3.00
3
TOP VIEW
RECOMMENDED LAND PATTERN
0.84
0.90
1.00 MAX
0.09
0.20
SEATING PLANE
0.30
0.50
0.95 BSC
0.00
0.10
SEE DETAIL "A"
FRONT VIEW
SIDE VIEW
GAUGE PLANE
0.25 BSC
0o-8o
NOTE:
0.30
0.50
ALL DIMENSIONS ARE IN MILLIMETERS.
6
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