ADP8140

Data Sheet

Rev. B | Page 14 of 23

Low Gain Buffer Power Control

In the low gain buffer power control mode, the ADP8140

multiplies the minimum voltage of the four current sinks by

This mode allows the ADP8140 to easily control nearly any

switched mode power supply (SMPS) control IC, such as a buck

regulator or boost controller. Common examples are shown in

Figure 32 to Figure 36.

In this mode, the COMP pin is connected to the feedback (FB)

input of an SMPS controller. The FB_OUT pin can be left

floating or connected to GND. Do not tie it to COMP or any

other pin. Connect the

A

A

pin to the EN signal of the SMPS

IC. This connection ensures that the power delivery immediately

shuts down in the event of a fault.

The values of R1, R2, and R3 program the minimum headroom

voltage on the SINKx pins and set the maximum voltage that

the SMPS FB input receives. A spreadsheet is available at

www.analog.com/ADP8140 to assist in these calculations.

Otherwise, to find the values start with the following equation:





















1

_

9

.

3

REF

FB

V

R1

R2

HR

where:

FB_REF is the internal error amplifier reference voltage of the

SMPS IC. This is typically 600 mV or 1.2 V. However, it does

vary for different ICs; therefore, consult the data sheet of that IC.

current sinks need (see Figure 7 to Figure 9). This value varies

based on the maximum sink current that is programmed on the

ISET pin.

Set the value of R1 to be small enough so that the internal

250 kΩ pull-down resistance on the COMP pin does not affect

and FB_REF = 600 mV, then

kΩ

1

.

11

1

6

.

0

325

.

0

9

.

3

kΩ

10

2























R

Next, select R3 to set the maximum voltage applied to the SMPS

FB input.

R2

R1

FB

R1

V

R3

MAX

REG









kΩ

6

.

20

k

11.1

kΩ

10

720

.

0

kΩ

10

V

3

3













R

FB_REF operating point. Some extra margin is beneficial.

DIMMING THE LED CURRENT

The ADP8140 offers multiple methods of dimming. The

dimming input can be either an analog voltage or a PWM

signal. The LED output current can be either scaled (dc

dimming) or pulsed on and off in response to the PWM input

signal. The two dimming pins, DIM and VT, provides different

functions, but both pins can be used for dimming simultaneously,

which provides enormous flexibility in controlling the LED

current.

Figure 23. Low Gain Buffer Power Control

SINK1

SINK2

SINK3

SINK4

ID1

ID2

ID4

ID3

BUCK OR BOOST IC

COMP

FB

R3

R2

R1

ADP8140

OPEN-DRAIN

BUFFER

SINK

CONTROL

8V/15V

MIN

600mV

MIN

AND

MAX

4×

250kΩ

VREG