T6309A [TMT]
Micropower Step-up DC/DC Converter; 微功率升压型DC / DC转换器
| 型号： | T6309A |
| 厂家： | 
TAIWAN MEMORY TECHNOLOGY |
| 描述： | Micropower Step-up DC/DC Converter |
| 文件： | 总13页 (文件大小：337K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
TE
tmCH
T6309A
Micropower Step-up DC/DC Converter
FEATURES
GRNERAL DESCRIPTION
• Matched LED Current with Overvoltage
Protection
The T6309A is a step-up DC/DC converter
that drives LED with a constant current. The
device can driver up to 6 series LEDs from a
single-cell Li-Ion battery. Series connection
of the LEDs provides constant LED current
that results in uniform brightness.
• Drives up to 6 LEDs in series
• Up to 85% Efficiency
• Low 400mV Feedback Reference,
Optional 1.19V Feedback Reference
• Internal Current Limit 300mA
• Under Voltage Lock Out Circuits
• 0.1uA Low Shutdown Supply Current
• 6-pin SOT-23 Package
The T6309A features a minimum off-time
current-limited PFM control scheme. The
LED current is set with an external sense
resistor (Rs) and is regulated by the feedback
pin (FB) that regulates the voltage across the
sense resistor to 400mV (typ). The low
400mV feedback reference voltage reduces
power loss and improves efficiency for LED
driver applications. Optional 1.19V feedback
reference is available for normal output
voltage applications like LCD bias. Output
overvoltage protection (OVP) is integrated to
prevent damage in case of output open circuit
condition (e.g. faulty LED). The OVP pin can
monitor the output voltage and turn off the
converter in the event of overvoltage
condition. The T6309A is available in SOT-
23-6 packages.
• ESD Human Body Mode Over 5KV
APPLICATIONS
• Cellular Phones
• Portable Communication Devices
• Handheld Electronics
• PDAs
• LED/Display Back Light Driver
PART NUMBER EXAMPLES
Feedback Referemce
Part no.
Voltage
400mV
1.19V
T6309A-AX
T6309A-BX
TM Technology Inc. reserves the right
P. 1
Publication Date: MAY. 2007
Revision: A
to change products or specifications without notice.
TE
tmCH
T6309A
PIN ARRANGEMENT
SOT23-6 (Top view)
SW
GND
FB
1
2
3
6
5
4
VIN
OVP
CE
PIN DESCRIPTION
SYMBOL
Pin No.
DESCRIPTION
Switch pin. Connect inductor/diode here. Minimize trace area at this
pin to reduce EMI.
SW
1
2
GND
Ground pin. Connect to local ground plane.
Feedback pin. Reference voltage is 400mV (T6309A-A). Optional
reference voltage is 1.19V (T6309A-B). Connect cathode of lowest
LED and current sense resistor here.
FB
CE
3
4
Chip enable pin. Tie CE pin to 1.5V or higher to enable device; 0.4V
or less to shutdown the device. Do not float this pin.
Overvoltage protection. Connect his pin to the output capacitor of
the converter.
OVP
5
6
VIN
Input supply pin. Must be locally bypassed.
BLOCK DIAGRAM
o v e r v o l t a g e
p r o t e c t i o n
m
i n i m u m
o f f - t i m
o n e - s h o t
u n d e r
O V P
+
-
e
v o l t a g e
V
I N
l o c k o u t
e r r o r
a m p l i f i e r
1 . 1 9 V
-
F B
c o n t r o l
l o g i c
S W
+
b u f f e r
d r i v e r
v o l t a g e
r e f e r e n c e
G N D
c u r r e n t
l i m i t
C E
Fig. 1
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T6309A
Absolute Maximum Ratings
Supply Voltage …………………………………………………………. -0.3V to 5V
SW Pin Switch Voltage ………………………………………………… -0.3V to 31V
OVP Pin Overvoltage Protection ……………………………………….. -0.3V to 31V
CE Pin Voltage …………………………………………………………. -0.3V to (VDD+0.3V)
SW Pin Switch Current ………………………………………………… 300mA
Continuous power dissipation, PD @ TA = 25°C SOT-23-6 …………. 0.35W
Package Thermal Resistance SOT-23-6, θJA ………………………….. 150°C /W
Operating Juction Temperature ………………………………………… 150°C
Operating temperature range …………………………………………… -40°C to +85°C
Storage temperature range, TSTG ……………………………………… -55°C to +150°C
Lead temperature (soldering, 10sec) …………………………………… 260°C
ESD Human Body Mode Over ……………………………………………5KV
Electrical Characteristics
( VIN=+3V, TA = 25°C, unless otherwise noted )
Symbol
Description
Conditions
Min. Typ. Max Unit
2.5
340 400 460 mV
VIN Input Voltage
5
V
T6309A-A
T6309A-B
VREF Reference Voltage
1.15 1.19 1.23
300 400 550
V
ns
V
uA
uA
V
TOFF Switch Minimum Off Time
VOVP Over voltage Threshold
22
60
IDD2 Switch Off Current (VOUT
IOFF Shutdown Current (VIN)
VIHCE CE Input Voltage Hight
VILCE CE Input Voltage Low
IICE CE Input Bias Current
)
FB=0.5V
CE=0V
0.1
1
1.5
0.4
0.1
0.1
uA
uA
IIFB FB Input Bias Current
UVLO Under Voltage Lockout
RDS(on) Switch ON Resistance
ILIM Current Limit
1.55 1.75 1.95
V
ohm
mA
0.6
300
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Publication Date: MAY. 2007
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tmCH
T6309A
Typical Operating Characteristics
(VIN=+3.3V,Load=4 LEDs, L=10uH, CIN=4.7uF, COUT=4.7uF, T A=+25 ºC, unless otherwise noted.)
Vin=3.1V
Load 4LED
Io=20mA
Efficiency (4WLED)
VFB Temperature curve
90
85
80
75
70
65
60
0.43
0.42
0.41
0.4
0.39
0.38
2.0
2.5
3.0
3.5
Vin(V)
4.0
4.5
5.0
-30 -20 -10
0
10 20 30 40 50 60 70
Temperature (°C)
Stabilityfor driving4LED/ Vin=3.6V
(time=1.0us/Div)
Stabilityfor driving4LED/ Vin=3.0V
(time=1.0us/Div)
Vout
1.0V/Div
Vsw
5.0V/Div
Vsw
5.0V/Div
Stabilityfor driving4LED/ Vin=5.2V
(time=1.0us/Div)
Vout
1.0V/Div
Vsw
5.0V/Div
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T6309A
Typical Operating Characteristics
(VIN=+3.3V,Load=6 LEDs, L=10uH, CIN=4.7uF, COUT=4.7uF, T A=+25 ºC, unless otherwise noted.)
Vin=3.1V Load
6LED
Efficiency (6WLED)
- Io=15mA
VFB Temperature curve
90
85
80
75
70
65
60
0.43
0.42
0.41
0.4
0.39
0.38
2.0
2.5
3.0
3.5
4.0
4.5
5.0
-30
-20
-10
0
10
20
30
40
50
60
70
Vin(V)
Temperature (ºC)
Stability for driving 6LED/Vin=3.0V
Stability for driving 6LED/Vin=3.6V
Vout
Vout
Vsw
Vsw
Stability for driving 6LED/Vin=5.2V
Vout
Vsw
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T6309A
Functional Description
transferred to output filter capacitor and the
load. As the energy stored in the inductor is
depleted, the current ramps down and the
output diode turns off. The output filter
capacitor stores the charge while the inductor
current is higher than the output current, then
sustains the output voltage until the next
switching cycle.
The T6309A is like a standard current-limit
PFM step-up DC-DC converter, but regulates
the voltage across the sense resistor Rs
instead of the output voltage. This results in a
constant LED current regardless the input
voltage and number of LEDs connected. With
integrated overvoltage protection (OVP), the
T6309A can be used as a current source with
overvoltage protection to drive LEDs. This
allows up to 6 LEDS to be connected in series
to the output. The low 400mV feedback
reference voltage reduces power loss and
improves efficiency.
Current Limit
The T6309A utilizes cycle-by-cycle
current limiting by means of protecting the
output MOSFET switch from overstress and
preventing the small value inductor from
saturation. Current limiting is implemented by
monitoring the output MOSFET current
build-up during conduction, and upon sensing
an over-current conduction immediately
turning off the switch for the duration of the
oscillator cycle. The current through the
output MOSFET is monitored and compared
against a reference signal. When the threshold
is reached, a signal is sent to the PFM
controller block to terminate the power switch
conduction. The current limit threshold is
typically set at 300mA.
Step-Up Converter
The step-up DC-DC converter operation
can be understood by referring to the block
diagram in Figure 1. PFM comparator
monitors the output voltage via the sense
resistor. When the feedback voltage is higher
than the reference voltage, the MOSFET
switch is turned off. As the feedback voltage
is lower than reference voltage and the
MOSFET switch has been off for at least a
period of minimum off-time decided by the
minimum off-time one-shot, the MOSFET
switch is then turned on one-shot, or until the
current limit signal is asserted.
During the internal MOSFET switch is turned
on, current ramps up in the inductor and store
energy in a magnetic field. When the
MOSFET is turned off, the voltage across the
inductor reverses and forces current through
the diode to the output filter capacitor and
load, so the energy in the inductor is
Overvoltage Protection
Since T6309A is configured as current
source, the output voltage rises as the output
impedance increases or output is open-circuit
(e.g. fault LED). The output voltage may
exceed the 22 V maximum voltage rating of
the internal main switch. An overvoltage
protection circuit is integrated to prevent the
main switch from burning. When the output
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T6309A
voltage exceeds the OVP threshold voltage,
the main switch is turned off. It remains off
until the output voltage falls below the OVP
threshold voltage. The step-up converter
continues normal operation as long as the
output voltage is under the OVP threshold.
Shutdown
The T6309A enters shutdown to reduce
quiescent current under 1uA when CE pin is
low . For normal operation, drive CE high.
During shutdown, the reference, all feedback
and control circuitry are off. The boost
converter’s output drops to one Schottky
diode voltage drop below the input voltage
and SW remains high impedance. The
capacitance and load at VOUT determine the
rate at which VOUT decays. The CE pin can
also be used as dimming control. More details
are in the dimming control section.
Undervoltage Lockout
An undervoltage lockout (UVLO) circuit
prevents fault operation of the T6309A when
input voltage is under 1.75V (typ). The device
remains off as long as the input voltage is
under the UVLO threshold.
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Publication Date: MAY. 2007
Revision: A
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tmCH
T6309A
Applications Information
• Select the maximum LED current IMAX
and 0mA as the minimum LED
current.
Dimming Control
There are several types of dimming control
circuit as follows:
• Calculate R2 to achieve a feedback current
in the range of I1 = 3uA to 10uA as the
LEDs are fully turned on:
R2 = VREF / I1 (e.g. 0.4V/4uA =100KOhm )
• Calculate R1 to meet the equation:
R1 / (R1+R2) = VREF / VMAX
(e.g. VREF=0.4V, VMAX=2.0V, R2=100KOhm,
the calculated R1 is 25KOhm)
• Calculate the sense voltage Vs at maximum
LED current:
1. Using a PWM signal to CE pin
When using a PWM signal at CE pin, the
T6309A is turned on or off by the PWM
signal. The average LED current increases
proportionally with the duty cycle of the
PWM signal. The typical frequency range of
the PWM signal is 150Hz to 250Hz. The
magnitude of the PWM signal should be
greater than the threshold voltage of CE
voltage high.
Vs = VREF x (1 + R1/R2)
(e.g. Vs = 0.4V x (1 + 25K/100K) = 0.5V)
• Calculate the sense resistor Rs:
Rs = Vs / IMAX
2. Using a DC voltage
A DC voltage signal can be used as well to
control the LED brightness. The dimming
control method is shown in the figure below.
When the DC voltage is zero, the LED is fully
turned on. As the DC voltage increases, the
voltage drop on R2 increases and the voltage
drop on R1 decreases. Thus the LED current
decreases. The selection of R1 and R2 should
make the current from the variable DC source
much smaller than the LED current and much
larger than the FB pin bias current.
(e.g. 0.5V/20mA = 25 Ohm)
3. Using a Filtered PWM signal
The filtered PWM signal can be considered as
an adjustable DC voltage. It can be used to
replace the DC voltage source if adjustable
analog signal is not available in the system.
The circuit is shown in the figure below:
T6309A
For VDC range from 0V to 2V, the selection of
resistors in this figure gives dimming control
of LED current from 0mA to 15mA.
Following steps are used to select the resistor
values:
FB
10K
PWM
Signal
RS
25 Ohm
R2
R1
• Select the voltage VMAX to turn the LEDs
off. (e.g. 2.0V)
100K 25K
0.1nF
• Select 0V as default to turn the LEDs fully
on.
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tmCH
T6309A
4. Using a Logic Signal
Output Voltage Selection
The LED current can be controlled in discrete
steps with a logic signal as shown in the
figure below. When the NMOS is off, R1 set
the minimum current. When the NMOS is on,
R2 sets the LED current increment value.
Referring to Fig. 4, select an output voltage
for T6309A-B (1.19V reference) by
connecting FB to a resistive divider between
the output and GND. The VOUT can be set as:
VOUT = (1+R1/R2) x 1.19V
Higher R1,R2 values reduce quiescent current,
but give bad noise immunity. To keep stable
feedback loop operation and better noise
immunity, select (R1+R2) value less than
1MOhm.
T6309A
FB
Logic
Signal
Inductor Selection
R2
R1
The T6309A is designed to work well with a
10uH inductor in most applications. Low
inductance values supply higher output
current, but also increase the ripple and
reduce efficiency. Higher inductor values
reduce ripple and improve efficiency, but also
limit output current. Choose a low DC-
resistance inductor, usually less than 1 Ohm
to minimize loss. It is necessary to choose an
inductor with saturation current greater than
the peak current that the inductor will
encounter in the application. Saturation
occurs when the inductor’s magnetic flux
density reaches the maximum level the core
can support and inductance falls. Inductor
with 600mA rating or greater would be
suitable for the T6309A.
Start-Up and Inrush Current
The T6309A has no internal soft start circuit
included to achieve minimum start-up delay.
All inductive step-up converters have higher
inrush current during start-up. The inrush
current for T6309A is about 200mA. If soft-
start is required, a recommended external
circuit is shown in the below figure.
D1
2.2nF
D2
T6309A
1K
FB
GND
RS
Capacitor Selection
4.7K
The input capacitor stabilizes the input
voltage and minimizes the peak current ripple
from the source. The value of the capacitor
depends on the impedance of the input source
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T6309A
used.
Small
ESR ( Equivalent Series
voltage larger than output voltage.
Resistance) ceramic capacitor with value of
1uF to 4.7uF would be suitable.
Layout Considerations
High switching frequencies make PC board
layout a very important part of design. Good
design minimizes excessive EMI on the
feedback paths and voltage gradients in the
ground plane, both of which can result in
instability or regulation errors.
Connect the inductor, input filter capacitor,
and output filter capacitor as close to the
device as possible, and keep their traces short,
direct, and wide to reduce power loss so as to
improve efficiency. Connect their ground pins
at a single common node in a star ground
configuration, or at a full ground plane.
The output capacitor should be placed close
to the output terminals to obtain better
smoothing effect on the output ripple.
The output capacitor is used to sustain the
output voltage when the internal MOSFET is
switched on and smoothing the ripple voltage.
The larger the output ripple, the larger the line
regulation, which means the LED current
changes if the input voltage changes. Low
ESR capacitor should be used to reduce
output ripple voltage. Use a 4.7uF to 10uF
ceramic output capacitor with about 50mOhm
to 150mOhm ESR to provide stable switching
and good line regulation.
Schottky Diode Selection
The diode is the largest source of loss in
DC-DC converters. The most important
parameters which affect the efficiency are the
forward voltage drop, VF, and the reverse
recovery time. The forward voltage drop
creates a loss just by having a voltage across
the device while a current flowing through it.
The reverse recovery time generates a loss
when the diode is reverse biased, and the
current appears to actually flow backwards
through the diode due to the minority carriers
being swept from the P-N junction. A
Schottky diode with the following
characteristics is recommended:
In addition, the ground connection for the
sense resistor Rs should be tied directly to the
GND pin and not shared with any other
component. This ensures a clean, noise-free
connection.
Small forward voltage, VF = 0.3 V
Small reverse leakage current Fast reverse
recovery time/switching speed Rated current
larger than peak inductor current Reverse
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T6309A
TYPICAL APPLICATION CIRCUITS
ILE D =20m A
L1
V IN
2.0
D 1
5
10uH
1
to
6
SW
5.5V
O V P
V IN
C IN
4.7uF
T 6309A
4
3
C E
FB
O N
G N D
R
S
2
C
O U T
O FF
20 O hm
4.7uF
Fig. 2 Typical application for driving 4 white LEDs
ILED=20m A
L1
VIN
2.0
Dim m ing
Control
0V~2V
D1
5
10uH
1
to
6
SW
5.5V
OVP
VIN
R2
100K
CIN
4.7uF
T6309A
4
3
CE
FB
ON
R1
25K
G ND
R
S
2
COUT
4.7uF
25 Ohm
OFF
Fig. 3 White LED application with DC voltage dimming control
L1
V IN
2.0
D 1
5
20m A
10uH
1
to
6
SW
5.5V
R 1
450K
O V P
V IN
C IN
4.7uF
T 6309A
4
3
C E
FB
O N
G N D
2
R2
33K
C
OU T
O FF
4.7uF
Fig. 4 Typical application for line drivers or LCD bias
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T6309A
TYPICAL APPLICATION CIRCUITS
ILE D =15m A
L1
V IN
2.0
D 1
5
10uH
1
to
6
SW
5.5V
O V P
V IN
C IN
4.7uF
T 6309A
4
3
C E
FB
O N
G N D
R
S
2
C
O U T
O FF
20 O hm
4.7uF
Fig. 5 Typical application for driving 6 white LEDs
ILED=15m A
L1
VIN
2.0
Dim m ing
Control
0V~2V
D1
5
10uH
1
to
6
SW
5.5V
OVP
VIN
R2
100K
CIN
4.7uF
T6309A
4
3
CE
FB
ON
R1
25K
G ND
R
S
2
COUT
4.7uF
25 Ohm
OFF
Fig. 6 White LED application with DC voltage dimming control
L1
V IN
2.0
D 1
5
15m A
10uH
1
to
6
SW
5.5V
R 1
450K
O V P
V IN
C IN
4.7uF
T 6309A
4
3
C E
FB
O N
G N D
2
R2
33K
C
OU T
O FF
4.7uF
Fig. 7 Typical application for line drivers or LCD bias
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T6309A
PACKAGE DIMENSIONS
SOT23-6
B
B 1
B 2
A 1
A
C 1
C
H
C 2
F
D
G
E
I
Dimension in mm
Symbol
Dimension in inch
Typ.
Min.
2.60
1.40
2.70
Typ.
2.80
Max.
3.00
1.60
3.00
Min.
Max.
0.118
0.063
0.118
A
A1
B
0.102
0.055
0.106
0.110
1.575
0.062
2.85
0.112
B1
B2
C
1.90(BSC)
0.95(BSC)
1.20
0.075(BSC)
0.037(BSC)
0.047
0.95
0.90
0
1.45
1.30
0.150
0.037
0.035
0
0.057
0.051
0.06
C1
C2
D
1.10
0.043
0.075
0.003
0.40
0.015
E
0.30
0.08
0.45
0.60
0.22
0.012
0.003
0.018
0.023
0.009
F
0.15
0.006
G
0.60(REF)
0~8°
5~15°
H
5~15°
I
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Revision: A
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