DA6251.002

27 October, 2017

10 (21)

DETAILED DESCRIPTION

MAS6251 operating modes are controlled by DIN and CTRL pins as follows.

Table 1. Operating modes

CONTROL INPUTS

OPERATING MODES

DIN

CTRL

DC/DC

OSC

PIEZO

LED

FB FET

MODE

LOW 1)

LOW 1)

OFF

OFF

OFF 2)

OFF

OFF

SHUTDOWN

LOW 1)

HIGH

ON

OFF

OFF 2)

ON

ON 3)

LED

HIGH

LOW 1)

ON

OFF

ON

OFF

OFF

PIEZO

HIGH

HIGH

ON

OFF

ON

ON

OFF

PIEZO+LED

Note 1: For DIN and CTRL

“LOW” means being low at least max 15ms

Note 2: Piezo

“OFF” is disable mode in which both piezo outputs are pulled to ground (VOB=VOS=GND)

Note 3: Feedback switch between FB and ILED is activated when only LED is driven

Both DIN and CTRL pins have internal pull-down by 400k

Ω which is disabled to save current when the inputs are

pulled high. When selecting DIN=CTRL=GND the device is in shutdown mode and consumes only very small

leakage current.

Capacitor and resistor values

The external CIN and COUT capacitors must be low loss (low ESR) ceramic capacitors. Recommended capacitor

and resistor values are shown in the table 2.

Table 2. Recommended capacitor and resistor values

Capacitor

Nominal value

CIN

10

F

COUT

100nF

CS

470pF

RB

1.5M

RF

200k

boost DC/DC converter output capacitor (COUT). Thus the output ripple can be reduced by choosing output

capacitor value which is much larger relative to piezo capacitance value. However note that large output capacitor

also lengthens output voltage rise time.

In piezo driving mode (DIN=HIGH or switching) the boost DC/DC converter output voltage can be controlled by

external voltage division resistors R1 and R2. See figures 3-4 and 8. The output voltage is regulated to level which

sets the FB feedback pin voltage to 0.4V typically. Table 3 shows example resistors values for different output

voltages. Note that the feedback resistors are not always necessary since when not connected the output voltage

will be regulated to over voltage protection (OVP) voltage 17.5V typically. See figures 1-2 and 5-7. When driving

only LEDs (CTRL=HIGH or PWM signal, DIN=LOW) the maximum output voltage (VOUT) is limited to OVP voltage

regardless of the FB pin connection.

Table 3. Feedback resistor (R1, R2) and DC/DC boost output voltage (VOUT) examples

R1

[kΩ]

R2 [M

Ω]

VOUT [V]

200

4.3

9

150

3.6

10

162

4.7

12

274

10

15

-

-

17.5

Note: VOUT=VFB*(1+R2/R1), VFB=0.4V