Data Sheet

ADP8140

Rev. B | Page 13 of 23

MODE PIN OPERATION

The MODE pin is used to program one of four possible modes

of operation. The condition of the MODE pin affects the DIM

pin input (see the Reducing the LED Current with the DIM Pin

section) and the power control mode (see Power Control Modes

section). The MODE pin state is read at power-up only, when

VIN crosses the UVLO threshold. After this point, the MODE

pin voltage is 0 V. The MODE status cannot change after power-up.

Table 5. Modes of Operation Programmed by the MODE Pin

MODE Connection

DIM Pin Mode

Power Control

GND

Analog voltage

Error amplifier

30.1 kΩ to GND

Analog voltage

Low gain buffer

52.3 kΩ to GND

PWM signal

Low gain buffer

REG

PWM signal

Error amplifier

POWER CONTROL MODES

Error Amplifier Power Control

In the error amplifier power control mode, the ADP8140

applies the minimum voltage of the four current sinks to the

inverting input of an internal error amplifier. The output of this

error amplifier connects to the FB_OUT inverting buffer.

The FB_OUT pin outputs a current, which indicates power

control. A higher FB_OUT sink current indicates that more

power is required to the LEDs. A lower FB_OUT sink current

indicates that less power is required for the LEDs. This

operation makes the FB_OUT ideal for any power control

application that does not normally have an error amplifier. The

two primary applications for this are as follows:



Controlling an optocoupler on the secondary side of an

isolated power supply



Controlling a PMOS transistor to regulate power in a fixed

output voltage supply.

Depending on the power stage used, an RC network must be

connected to the COMP pin. The COMP pin connects to the

output of the FB_OUT transconductance amplifier. To select

the COMP resistor and capacitor values, a free simulation tool,

ADIsimPE, is available at: www.analog.com/ADIsimPE.

Using this tool, and the included ADP8140 circuit model, the

loop control and stability can be easily simulated and adjusted

for different setups.

Figure 22. Error Amplifier Power Control

SINK1

SINK2

SINK3

SINK4

ID1

ID2

ID4

ID3

SHUTDOWN

SINK

CONTROL

SINK_EN

8V/15V

FB_OUT

MIN

CH_OVP

5.7V

MAX

COMP

MIN

AND

MAX