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TPS61160

TPS61161

SLVS791C – NOVEMBER 2007 – REVISED APRIL 2012

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DETAILED DESCRIPTION

OPERATION

The TPS61160/1 is a high efficiency, high output voltage boost converter in a small package size. The device is

ideal for driving white LED in series. The serial LED connection provides even illumination by sourcing the same

output current through all LEDs, eliminating the need for expensive factory calibration. The device integrates

40V/0.7A switch FET and operates in pulse width modulation (PWM) with 600kHz fixed switching frequency. For

operation see the block diagram. The duty cycle of the converter is set by the error amplifier output and the

current signal applied to the PWM control comparator. The control architecture is based on traditional current-

mode control; therefore, a slope compensation is added to the current signal to allow stable operation for duty

cycles larger than 50%. The feedback loop regulates the FB pin to a low reference voltage (200mV typical),

reducing the power dissipation in the current sense resistor.

SOFT START-UP

Soft-start circuitry is integrated into the IC to avoid a high inrush current during start-up. After the device is

enabled, the voltage at FB pin ramps up to the reference voltage in 32 steps with each step taking 213

μs. This

ensures that the output voltage rises slowly to reduce the input current. Additionally, for the first 5msec after the

COMP voltage ramps, the current limit of the switch is set to half of the normal current limit spec. During this

period, the input current is kept below 400mA (typical). See the start-up waveform of a typical example,

Figure 11.

OPEN LED PROTECTION

Open LED protection circuitry prevents IC damage as the result of white LED disconnection. The TPS61160/1

monitors the voltage at the SW pin and FB pin during each switching cycle. The circuitry turns off the switch FET

and shuts down the IC when both of the following conditions persist for 8 switching clock cycles: (1) the SW

output voltage falls to the level of the input supply. The device remains in shutdown mode until it is enabled by

toggling the CTRL pin logic. To allow the use of inexpensive low-voltage output capacitor, the TPS61160/1 has

different open lamp protection thresholds. The threshold is set at 26V for the TPS61160 and 38V for the

TPS61161. Select the appropriate device so that the product of the number of external LEDs and each LED's

maximum forward voltage plus the 200mV reference voltage does not exceed the minimum OVP threshold or

SHUTDOWN

The TPS61160/1 enters shutdown mode when the CTRL voltage is logic low for more than 2.5ms. During

shutdown, the input supply current for the device is less than 1

μA (max). Although the internal FET does not

switch in shutdown, there is still a DC current path between the input and the LEDs through the inductor and

Schottky diode. The minimum forward voltage of the LED array must exceed the maximum input voltage to

ensure that the LEDs remain off in shutdown. However, in the typical application with two or more LEDs, the

forward voltage is large enough to reverse bias the Schottky and keep leakage current low.

CURRENT PROGRAM

The FB voltage is regulated by a low 0.2V reference voltage. The LED current is programmed externally using a

(1)

Where

The output current tolerance depends on the FB accuracy and the current sensor resistor accuracy.

8

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