4

dc2641af

DEMO MANUAL DC2641A

FREQUENCY SYNCHRONIZATION AND MODE SELECTION

Table 1. Mode Selection and Synchronized Operation Options

CONFIGURATION

JP4

MODE WITH SYNC. SIGNAL APPLIED TO PLLIN

Forced Continuous Operation

FCM

FCM

Pulse-Skipping Operation

P.S.

P.S.

Burst Mode Operation with Adjustable Clamp Level

Burst ADJ.

FCM

Burst Mode Operation with Default Clamp

Burst Default

FCM

Table 2. Optional Inductor DCR Current Sensing

CONFIGURATION

RS1

R24

R28

C16

R37

R38

R39

R40

Current Sense Resistor (Default)

Ref. Sch.

Ref. Sch.

Ref. Sch.

OPEN

OPEN

OPEN

OPEN

OPEN

Inductor DCR Current Sensing

0Ω Copper

OPEN

OPEN

Calculated Value from Data Sheet

0Ω

0Ω

Demonstration circuit 2641A’s Mode selector allows the

converter to run in forced continuous operation, pulse-

skipping operation, Burst Mode or Burst mode with

adjustable clamp level by changing the position of JP4.

To synchronize the DC2641A to an external clock, apply

the sync signal to the PLLIN turret. Depending upon the

JP4 setting, the DC2641A will operate in different modes.

See Table 1 for the detailed description.

100% DUTY

Demonstration circuit 2641A features 100% duty cycle

operation in dropout. Set the JP5 to “ON” position to acti-

vate this feature. Set JP5 to “OFF” position disables the

internal charge pump and enables boost refresh, allowing

for 99% duty cycle operation in dropout.

OPTIONAL INDUCTOR DCR CURRENT SENSING

Demonstration circuit 2641A provides an optional circuit

for Inductor DCR Current Sensing. Inductor DCR Cur-

rent Sensing uses the DCR of the inductor to sense the

inductor current instead of discrete sense resistors. The

advantages of DCR sensing are lower cost, reduced board

space and higher efficiency, but the disadvantage is a less

accurate current limit. If DCR sensing is used, be sure to

select an inductor current with a sufficiently high satura-

tion current or use an iron powder type material.

Refer to Table 2 for Optional Inductor DCR Current Sens-

ing setup and to the data sheet for more details.

Low Quiescent Current Applications and Measurement

ler is 40µA in sleep mode as specified in the LTC7801

data sheet. However, the input current of the DC2641A

board can be higher than this value because of additional

circuit outside of the IC. To reduce the total input current,

large value FB divider resistors should be used. In addi-

tion, some jumpers and resistors should be configured

accordingly. Refer to Table 3 for the low input quiescent

current setup.

Table 3. Low Input Quiescent Current Configuration

REFERENCE DESIGNATOR

R1

R2

R23

JP3

JP4

JP5

JP8

Function

OVLO

PGOOD

MODE Selector

100% DUTY

BIAS supply

Stuffing Option

OPEN

0Ω

OPEN

OPEN

BURST ADJ. or

BURST DEFAULT

OFF

OFF