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PDF T8308 Data sheet ( Hoja de datos )
| Número de pieza | T8308 | |
| Descripción | PWM Control 800mA Step-Down Converter | |
| Fabricantes | TM Technology | |
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tm TE
CH
T8308
PWM Control 800mA Step-Down Converter
FEATURES
• Wide Input Voltage Range: 7V to 30V
• LED Output Current Up to 800mA
• Soft-start
• Single pin on/off and brightness control
using DC voltage or PWM
• High efficiency (up to 97%)
• Up to 1MHz switching frequency
• Typical 5% output current accuracy
• SOT-89 and SOP-8 Lead-free Package
Applications
• LED/Display Back Light Driver
• Lightings
• Portable Communication Devices
• Handheld Electronics
GENERAL DESCRIPTION
The T8308 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 30V and
provides an externally adjustable output
current of up to 800mA. Depending upon
supply voltage and external components, this
can provide up to 24 watts of output power.
The T8308 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 T8308 is available
in SOT-89 and SOP-8 Lead-free package.
PART NUMBER EXAMPLES
PART NO.
T8308-AX
T8308-AD
PACKAGE
SOT-89
SOP-8
TM Technology, Inc. reserves the right
P. 1
to change products or specifications without notice.
Publication Date: Oct. 2014
Revision:C
1 page  
tm TE
CH
T8308
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 EN pin of the device is unconnected and the
voltage on this pin (VEN) appears directly at the (+) input of the comparator。
When input voltage VIN 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 VIN to ground, via RS, L1 and the LED(s). The current rises at a rate determined by VIN
and L1 to produce a voltage ramp (VSENSE) across RS. The supply referred voltage VSENSE 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 MN is off, the current in L1 continues to flow via D1 and the LED(s) back to
VIN. 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.
Switching thresholds
Define an average VSENSE switching threshold of 100mV (measured on the ISENSE pin with
respect to VIN). The average output current IOUTnom is then defined by this voltage and RS
according to:
IOUTnom = 100mV/RS
Nominal ripple current is ±15mV/RS
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
P. 5
to change products or specifications without notice.
Publication Date: Oct. 2014
Revision:C
5 Page | ||
| Páginas | Total 10 Páginas | |
| PDF Descargar | [ Datasheet T8308.PDF ] | |
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