ADP8140

Data Sheet

Rev. B | Page 12 of 23

Figure 21. Start-Up Timing and Signals

CURRENT SINKS

The ADP8140 contains four internal current sinks. Each

current sink is capable of delivering 125 μA to 500 mA. To

ensure accurate regulation, the voltage on the current sinks

must be greater than the maximum headroom voltage given in

Table 1. For additional information on the headroom voltage,

see Figure 7 to Figure 9. All current sinks have their maximum

in Figure 14.

(mA)

2560

)

(kΩ

SINK

SET

I

R



(1)

Multiple sinks can be combined together for higher currents per

LED string. For example, two sinks can be shorted together to

drive two strings of LEDs, each at up to 1 A, or four sinks

combined to drive one string of LEDs at up to 2.0 A.

A resistor must always be connected to the ISET pin. However,

in the event that ISET is accidentally left open, the ADP8140

defaults to a typical current of 15 mA (typical) per sink. If ISET

is accidentally shorted to GND, the ADP8140 limits the current

per sink to 570 mA (typical) and shuts down the power stage

(

A

A

goes low and FB_OUT and COMP are disabled).

Each current sink has a maximum rated voltage of 20 V.

However, the maximum output voltage driving all the current

sinks, through the LEDs, is allowed to exceed 20 V. The LEDs

drop enough voltage so that the SINKx voltage remains close to

reference voltage). Because the ADP8140 controls the power

stage, the voltage is not present when off or during a fault.

Therefore, the ADP8140 can be safely used in conjunction with

power supplies that produce over 100 V for their output.

POWER CONTROL OPERATION

The ADP8140 controls a power stage with its COMP and

FB_OUT pins. The power stage allows the IC to optimize the

efficiency and protection of the LEDs. The ADP8140 operates

in two power control modes: error amplifier and low gain

buffer. The MODE pin is used to select the power control mode.

3.0V

UVLO

VIN

REG

EN

SHUTDOWN

SHUTDOWN

100µs

VREG OK AND UVLO OK AND EN HIGH

DETERMINE MODE STATE

~8ms

SINK_EN

(INTERNAL)

MODE_STATE

(INTERNAL)

FAULT

(EXT RESISTOR

PULL-UP)

COMP

(EA CONFIG)

COMP

(BUFFER CONFIG)

FB_OUT

(EA CONFIG)

DETERMINE (ONE OF 4 STATES) UNTIL REG OR VIN POWERS DOWN