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We are working on an LED dimmer circuit which supports DALI2.0 Interface. We already received the hardware and working on software only. LED driver circuit is based TPS92515HV and below is the circuitry

enter image description here

But the issue is LED is not switching off even if the control signal which is Iadj is 0. We tried shorting Iadj to GND and still, there is a current of 3.5mA through LED which makes LED on always unless power is removed. This will lead to non-complinace of DALI OFF command. The board is powered externally and we cannot control it and also we cannot afford any major component addition like relays to control power line to the driver chip. Is there anything to do with TPS92515HV configuration.??

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  • \$\begingroup\$ What does the datasheet say? Far from all LED drivers can regulate down to 0 mA, save for forcing EN low. \$\endgroup\$ – winny Sep 29 '17 at 10:27
  • \$\begingroup\$ @winny There is no EN pin on chip \$\endgroup\$ – raforanz Sep 29 '17 at 10:43
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    \$\begingroup\$ @raforanz: It has a pwm pin \$\endgroup\$ – PlasmaHH Sep 29 '17 at 10:47
  • \$\begingroup\$ What's the value of VLED a) when operating at full brightness and b) when it's still putting out 3.5mA? \$\endgroup\$ – Finbarr Sep 29 '17 at 11:24
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    \$\begingroup\$ Why are you putting your PWM on IADJ? That should surely be going to the PWM pin? (Unless this is something about the DALI interface I don't understand): Did you look at the typical application schematic? \$\endgroup\$ – loudnoises Sep 29 '17 at 11:51
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The datasheet in section 8.3.11 PWM (UVLO and Enable) says

Because the PWM pin is also UVLO (undervoltage lockout and device enable), when pulled low it is necessary to ensure the output is 100% OFF. The high-side FET driver has a small leakage path to the output. Although very small (<<100 μ A), theLEDs could glow if the current was not eliminated. The 100- μ A (typical) pulldown is activated and held ON while PWM is low and ensures no light output

so disable the driver when you want to turn it off by pulling the PWM pin low from your micro.

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