Datasheet

TPS92551, TPS92551EVM
www.ti.com SNVS805C –MAY 2012–REVISED MAY 2013
Peak Switch Current Limit
The TPS92551 features an integrated switch current limiting mechanism to prevent the LEDs from being over-
driven. The switch current limiter is triggered when the switch current is three times exceeding the current level
set by resistor. Once the current limiter is triggered, the internal power switch turn OFF for 3.6µs to discharge the
inductor until inductor current reduces back to normal level. The current limiting feature is exceptionally important
to avoid permanent damage of the TPS92551 application circuit due to short circuit of LED string.
PWM Dimming Control
The DIM pin of the TPS92551 is an input with internal pull-up that accepts logic signals for average LED current
control. Applying a logic high (above 1.3V) signal to the DIM pin or leaving the DIM pin open will enable the
device. Applying a logic low signal (below 0.7V) to the DIM pin will disable the switching activity of the device but
maintain operation of the VCC regulator active. The TPS92551 operation of high speed dimming and very fine
dimming control as shown in Figure 33.
Figure 33. Shortened Current Slew up Time of the TPS92551
To ensure normal operation of the TPS92551, it is recommended to set the dimming frequency not higher than
1/10 of the switching frequency. The dim pulse on time is tested down to 16µs. In applications that require high
dimming contrast ratio, low dimming frequency should be used.
Parallel Operation
When a load current higher than 450mA is required by the application, TPS92551 can be used in parallel to
deliver higher current. With common VINs and GNDs, the TPS92551 will operate as independent asynchronous
current sinks driving the same LED load. The total DC current of the modules will be additive; however, low
frequency sub-harmonic current ripple may be present and its frequency and magnitude will depend upon the
phase relationship between the internal clocks as there is no provision for synchronizing driver clocks. It is
suggested to have minimum 2.2μF C
OUT
located close the module to filter out the current ripple , and the
resultant LED current will become DC. Current sharing modules should have a local C
IN
capacitor of minimum
2.2μF located as close to V
IN
and GND as possible. Refer to Figure 33 for the TPS92551 parallel operation
circuit schematic. Refer to Figure 35 for the TPS92551 parallel operation results I
LED
vs V
IN
.
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