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TPS61177A Usage and Programming
6.4.3
Dimming Mode Settings
The TPS61177A has 3 different types of LED dimming mode.
1. Direct PWM mode bypasses PWM input duty and freq to dimming output with same duty and freq. In
this case, large output load can switch potentially causing instability of the system such as power
fluctuation and audible noise. This mode is not recommended for generic applications.
2. Analog mode changes brightness value from PWM input into constant current value to dimming output.
System is more stable than direct PWM mode as there is no huge load transition condition.
3. Analog and PWM Mixed mode includes the advantages of both PWM and analog mode. Input PWM
duty is calculated to generate constant analog dimming output from 100% to 25% brightness. Analog
to PWM mode transition happens at 25% brightness. The duty of output PWM dimming signal will be
4x of input PWM duty below 25% as max current value will be only quarter of 100% brightness.
6.5
Support for Fault Conditions
6.5.1
Thermal Shutdown
The TPS61177A will shut down the LED outputs and the boost if the temperature exceeds 150°C. The
device will exit thermal shutdown when the temperature drops below 135°C.
6.5.2
Undervoltage Lockout
The TPS61177A will not start up until the VINB voltage is higher than the UVLO threshold which is preset
by EEPROM register data. During normal operation, if the VINB drops below UVLO with 200-mV
hysteresis, the TPS61177A immediately shuts down. There are 5 different UVLO levels from 2.25 V to 4
V.
6.5.3
Undervoltage Lockout
The TPS61177A will not start up until the VINB voltage is higher than the UVLO threshold which is preset
by EEPROM register data. During normal operation, if the VINB drops below UVLO with 200-mV
hysteresis, the TPS61177A immediately shuts down. There are 5 different UVLO levels from 2.25 V to 4
V.
6.5.4
Overvoltage Protection
The TPS61177A integrates output OVP which is fixed at 39.5 V typically. Once the VLED pin detects the
voltage higher than 39.5 V, the boost switching regulator stops switching until the voltage of VLED pin
drop below 39.5 V with 500-mV hysteresis.
6.5.5
Undervoltage Lockout
The TPS61177A has a pulse-by-pulse overcurrent limit of 1.8 A (minimum). The PWM switch turns off
when the inductor current reaches this current threshold. This protection can be disabled by EEPROM
register control (ILIM).
6.6
ID Register
The device slave register of TPS61177A is 58h in 8-bit (7bit slave a R/W bit) or 2Ch in 7-bit
without R/W bit.
6.7
EEPROM Default Values
Refer to TPS61177A data sheet
(SNVSA76)
for detailed descriptions.
25
SNVU490 – OCTOBER 2015
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