tm
Features
TE
CH
Preliminary
T8306
PWM Control 36V Step-Down Controller
General Description
The T8306 is a continuous mode inductive
step-down converter, designed for driving
single or multiple series connected LEDs
efficiently from a voltage source higher than
the LED voltage. The device operates from an
input supply between 7V and 36V and provides
an externally adjustable output current of up to
3A. Depending upon supply voltage and
external components, The T8306 includes the
output switch and a high-side output current
sensing circuit, which uses an external resistor
to set the nominal average output current. The
T8306 is available in SOT23 Lead-free package.
• Wide Input Voltage Range: 7V to 36V
• LED Output Current Up to 3A
• With External Power MOSFET
• Soft-start
• Single pin on/off and brightness control
• High efficiency (up to 95%)
• Up to 1MHz switching frequency
• Typical 5% output current accurac
y
• SOT-23 Lead-free Package
Applications
• CCTV IR LED Driver
• Lightings
• Portable Communication Devices
• Handheld Electronics
Part Number Examples
PART NO.
T8306AX
PACKAGE
SOT23
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to change products or specifications without notice.
P. 1
Publication Date: May. 2013
Revision:A
tm
TE
CH
T8306
Pin Arrangement(Top view)
T8306AX
SOT23-6
Pin Description
SYMBOL
SOP-8
DESCRIPTION
I
SENSE
EN
V
IN
VCC
GD
GND
1
2
3
4
5
6
Connect resistor R
S
from this pin to V
IN
to define nominal average
output current I
OUTnom
= 0.2/R
S
Enable control signal, H: Ative, L : Power Down
Input voltage . Decouple to ground with 10uF or higher X7R
ceramic capacitor close to device
12V LDO output
External Power MOSFET Gate Driver
Ground
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to change products or specifications without notice.
P. 2
Publication Date: May. 2013
Revision: A
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Parameter
TE
CH
T8306
Symbol
VIN
Absolute Maximum Ratings
Value
-0.3 to +38
-5 to +0.3
-0.3 to +6
-0.3 to +12
TA
TLEAD
TS
SOT23
SOT23
-40 to +125
300
-65 to +150
0.35
250
Unit
V
V
V
V
°C
°C
°C
W
°C/W
Voltage on intput pin relative to GND
ISENSE pin Voltage (Measured with respect to Vin)
EN pin Voltage
GD pin Voltage
Operating Temperature Rang
Maximum Soldering Temperature (at leads, 10 sec)
Storage Temperature Rang
Power debauchery, PD @ TA = 25°C
Package Thermal Resistance,
θJA
Electrical Characteristics
(TA = -40 to 85°C unless otherwise noted. Typical values are at TA =25°C, VIN =12V)
Symbol
Description
V
IN
Input Voltage
V
IRU
V
IRD
I
QOFF
I
QON
V
SENSE
Internal regulator start-up threshold
Internal regulator shutdown
Quiescent supply current
with output off
Quiescent supply current
with output switching
Conditions
V
IN
rising
V
IN
falling
EN pin grounded
f = 80kHz
Min. Typ. Max
7
-
36
7
6.5
170
1.8
190
200
±20
300
3.0
210
Unit
V
V
V
uA
mA
mV
%
Mean current sense threshold Voltage
Measured on I
SENSE
pin with respect to
(Defines LED current setting accuracy)
V
SENTH
Sense threshold hysteresis
I
SENSE
V
IHEN
V
ILEN
Tr
Tf
I
SENSE
pin input current
EN Input Voltage Hight
EN Input Voltage Low
Rise Time of GD
Fall Time of GD
V
SENSE
=V
IN
– 0.2
2
20
30
0.5
uA
V
V
ns
ns
V
V
@Cload = 1600pF
@Cload = 1600pF
Vin
≧ 14V
100
100
12
Vin-
2V
0.2
167
V
GDO,H
GD Pin out Voltage, at High Stage
Vin
＜ 14V
V
GDO,L
GD Pin out Voltage, at Low Stage
T
TP
Thermal Shutdown Protect
V
°C
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to change products or specifications without notice.
P. 3
Publication Date: May. 2013
Revision: A
tm
f
GD
TE
CH
T8306
Electrical Characteristics
(
continuous)
Operating frequency
L = 47uH (0.093 ohm)
I
OUT
=2A @V
LED
= 3.6V Driving 1 LED
GD High State
GD Low State
GD High State
80
3
*
6
*
12
1
0.3
2
0.7
KHz
us
us
us
MHz
T
ONmin
Minimum switch ‘ON’ time
T
OFFmin
Minimum switch ‘OFF’ time
T
ONminR
time
f
GDmax
D
GD
T
PD
Recommended minimum switch 'ON'
Recommended maximum operating
frequency
Recommended duty cycle range of
output switch at
f
GDmax
Internal comparator propagation delay
us
Notes :
*Parameters are not tested at production. Parameters are guaranteed by design, characterization and process
control.
Block Diagram
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to change products or specifications without notice.
P. 4
Publication Date: May. 2013
Revision: A
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TE
CH
T8306
Functional Description
The device, in conjunction with the coil (L1) and current sense resistor (RS), forms a selfoscillating
continuous-mode buck converter.
Device operation
Operation can be best understood by assuming that the Vref of the device is unconnected and the
voltage on pin appears directly at the (+) input of the comparator.
When input voltage V
IN
is first applied, the initial current in L1 and RS is zero and there is no
output from the current sense circuit. Under this condition, the (-) input to the comparator is at
ground and its output is high. This turns MN on and switches the LX pin low, causing current to
flow from V
IN
to ground, via RS, L1 and the LED(s). The current rises at a rate determined by V
IN
and L1 to produce a voltage ramp (V
SENSE
) across RS. The supply referred voltage V
SENSE
is
forced across internal resistor R1 by the current sense circuit and produces a proportional current in
internal resistors R2 and R3. This produces a ground referred rising voltage at the (-) input of the
comparator. When this reaches the threshold voltage, the comparator output switches low and MN
turns off. The comparator output also drives another NMOS switch, which bypasses internal resistor
R3 to provide a controlled amount of hysteresis. The hysteresis is set by R3 to be nominally 20% .
When MN is off, the current in L1 continues to flow via D1 and the LED(s) back to V
IN
. The
current decays at a rate determined by the LED(s) and diode forward voltages to produce a falling
voltage at the input of the comparator. When this voltage returns , the comparator output switches
high again. This cycle of events repeats, with the comparator input ramping between limits of ±
20%.
Switching thresholds
With V
REF
the ratios of R1, R2 and R3 define an average V
SENSE
switching threshold of 200mV
(measured on the I
SENSE
pin with respect to V
IN
). The average output current I
OUT
nom is then
defined by this voltage and R
S
according to:
I
OUTnom
= 200mV/R
S
Output shutdown
The output of the low pass filter drives the shutdown circuit. When the input voltage to this circuit
falls below the threshold, the internal regulator and the output switch are turned off. The voltage
reference remains powered during shutdown to provide the bias current for the shutdown circuit.
Quiescent supply current during shutdown is nominally 35uA and switch leakage is below 5uA.
TM Technology, Inc. reserves the right
to change products or specifications without notice.
P. 5
Publication Date: May. 2013
Revision: A
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