Texas Instruments TPS65820 Evaluation Module TPS65820EVM TPS65820EVM 데이터 시트
제품 코드
TPS65820EVM
WHITE LED CONSTANT CURRENT DRIVER
L3
3.3 H
m
SM3
PGND3
FB3
P3
P3
OUT
GATE
DRIVE
GATE
DRIVE
500 mA
+
_
INDUCTOR PEAK
CURRENT
DETECTION
LED LOW CURRENT
DETECTION
+
_
OUTPUT OVP
DETECTION
+
_
CONTROL LOGIC AND
MINIMUM OFF TIME
MAXIMUM ON TIME
SOFT
START
DUTY CYCLE
CONTROL
OFF
OFF
ON EN
ON
LED SWITCH
FREQUENCY
FREQUENCY
AND DUTY
CYCLE
TPS65820
250 mV
I2C REGISTER
28V
LED
SWITCH
POWER
STAGE
SWITCH
LSM3
D1
SM3_SW
R
10
FB3
W
C27
1 F
m
SLVS663B – MAY 2006 – REVISED APRIL 2008
..............................................................................................................................................................
www.ti.com
The TPS65820 has an integrated boost converter (SM3) that is optimized to drive white LEDs connected in a
series configuration. Up to six series white LEDs can be driven, with programmable current and duty cycle
adjustable via a dedicated I
series configuration. Up to six series white LEDs can be driven, with programmable current and duty cycle
adjustable via a dedicated I
2
C register.
The SM3 boost converter (SM3) has a 30-V, 500-mA, low-side integrated power stage switch that drives the
external inductor. Another integrated 30-V, 25-mA switch (LED switch) is used to modulate the brightness of the
external white LEDs. A simplified block diagram is shown in
external inductor. Another integrated 30-V, 25-mA switch (LED switch) is used to modulate the brightness of the
external white LEDs. A simplified block diagram is shown in
Figure 54. Simplified Block Diagram
The SM3 converter operates like a standard boost converter. The LED current is defined by the value of the
external resistor R
external resistor R
FB3
, connected from pin FB3 to AGND1. The integrated power stage switch control monitors
the LED switch current (FB3) and the integrated power stage switch current, implementing a topology that
effectively regulates the LED current independently of the input voltage and number of LEDs connected. The
high voltage rating of the integrated switches enables driving up to six white LEDs, connected in a series
configuration.
effectively regulates the LED current independently of the input voltage and number of LEDs connected. The
high voltage rating of the integrated switches enables driving up to six white LEDs, connected in a series
configuration.
The internal LED switch, in series with the external LEDs, disconnects the LEDs from ground during shutdown. In
addition, the LED switch is driven by a PWM signal that sets the duty cycle, enabling adjustment to the average
LED current by modifying the settings of the I
addition, the LED switch is driven by a PWM signal that sets the duty cycle, enabling adjustment to the average
LED current by modifying the settings of the I
2
C register SM3_SET. With this control method, the LED brightness
depends on the LED switch duty cycle only, and is independent of the PWM control signal.
The duty cycle control used in the SM3 converter LED switch is implemented by generating a burst of high
frequency pulses, with a pattern that is repeated periodically. For a duty cycle of 50%, all of the high frequency
pulses have a 50% duty cycle. The duty cycle control sets individual pulses to 100% duty cycle when increasing
the LED_PWM output duty cycle; for decreasing LED_PWM output duty cycles, individual pulses are set to 0%
duty cycle. An example of distinct duty cycles is shown in
frequency pulses, with a pattern that is repeated periodically. For a duty cycle of 50%, all of the high frequency
pulses have a 50% duty cycle. The duty cycle control sets individual pulses to 100% duty cycle when increasing
the LED_PWM output duty cycle; for decreasing LED_PWM output duty cycles, individual pulses are set to 0%
duty cycle. An example of distinct duty cycles is shown in
, the sum of the individual pulses on/off time
over the repetition period are equivalent to the duty cycle obtained with traditional single-pulse duty cycle circuits.
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