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SOFT START

ENABLE (EN1, EN2)

UNDERVOLTAGE LOCKOUT

SHORT CIRCUIT AND OVERTEMPERTURE PROTECTION

OVERVOLTAGE PROTECTION AT VOUT

TPS60230

SLVS516A – MAY 2004 – REVISED JUNE 2004

DETAILED DESCRIPTION (continued)

The TPS60230 has an internal soft start circuit to limit the inrush current during startup. This prevents possible

voltage drops of the input voltage if a high impedance power source is connected to the input of the TPS60230.

When the device starts up with an output voltage that is below the input voltage, the output capacitor is charged

directly from the input with a current source. The output current increases linearly until the output reaches within

300 mV of the input voltage. When the programmed output current can be reached with the 1x mode, the

TPS60230 terminates the soft start and begins normal operation. When the desired output current cannot be

reached, the charge pump begins operation in 1.5x mode and pumps the output voltage up to the needed level

to reach the programmed output current.

The enable pins EN1 and EN2 are used to enable the device or set it into shutdown. The TPS60230 is enabled if

one of the enable pins is pulled higher than the enable trip point of 1.3 V. The device starts up by going through

the soft start routine as described in the section Soft Start. Pulling both pins to GND, after a delay, programs the

device to shutdown. In shutdown, the charge pump, current sources, voltage reference, oscillator, and all other

functions are turned off and the supply current is reduced to 0.1 µA.

EN1 and EN2 can also be used for dimming. The logic levels at EN1 and EN2 set the minimum voltage at the

current mirrors and the voltage at the ISET pin to GND. This sets the current at the LEDs to be either the full

current or a fraction of the full current. See Table 1 for further details. The maximum current through the LEDs is

set by a resistor connected between ISET and GND.

EN1 and EN2 can also be used for PWM dimming. The PWM signal can either be applied to EN1 or EN2, or

both inputs can be tied together and the PWM signal can be applied to both pins. Depending on the

configuration, the current during PWM dimming is switched between 0 mA and its maximum (EN1 and EN2

connected to the PWM signal) or between 0 mA and 1/3 of the full LED current if EN2 = 0 and EN1 is toggled.

When EN1 = 0 and EN2 is toggled, the output current can be changed between 0 mA and 2/3 of the full range.

Table 1. Enable Levels

ENABLE LEVEL

MODE

LED CURRENT

EN2

EN1

0

0

SHUTDOWN

0

0

1

VISET = 200 mV

1/3

1

0

VISET = 400 mV

2/3

1

1

VISET = 600 mV

Full

The undervoltage lockout circuit shuts down the device when the voltage at VIN drops below a typical threshold

of 2.15 V. This prevents damage to the device. The UVLO circuit allows the device to start up again after the

voltage on the VIN pin has increased by about 100 mV above the UVLO lockout threshold.

The current at the VOUT pin is limited typically to 250 mA. When the junction temperature exceeds 155

°C, the

device shuts down to protect the device from damage. After the temperature decreases to about 135

°C, the

device starts up again if it is enabled.

The device uses the voltage at D1 to regulate voltage at VOUT. In case D1 is not connected, an overvoltage

protection circuit ensures that the output voltage at VOUT does not exceed its limits. The connection of the LEDs

must be started using D1 first. For all other LEDs there is no restriction in the sequence. For example, if there

are only 3 LEDs used, the first LED is connected to D1 and the other two LEDs can be connected to any other of

the D2 to D5 pins.

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