DA6250.007

13 April, 2018

14 (24)

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 9-12. 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 5-8. 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

VIN/(R1+R2) since VOUT follows VIN voltage when the device is in shutdown. To keep the shutdown current low

the external feedback resistance (R1+R2) should be close to 10M

 level. For good feedback regulation the max

R1 should not exceed 400k

.

When driving LEDs they are connected in series from VOUT to ILED which is the current sink pin. Additionally

LED current setting resistor RLED needs to be connected from RLED pin to GND. See figures 4-6 and 10. The

table 4 shows example RLED resistor values and corresponding LED current levels. Additionally PWM signal can

be applied to the CTRL pin for LED dimming to reduce average LED current from level defined with the RLED

resistor.

Table 4. LED current setting resistor examples

RLED

[

Ω]

ILED

[mA]

40.2

5.0

20

10.0

13.3

15.0

Note: ILED=VRLED/RLED, VRLED=0.2V typ

In self-drive mode (frequency adjustment resistor connected from ROSC pin to GND) the piezo audio signal

frequency is generated from an internal oscillator. The oscillator frequency is controlled by external oscillator

resistor ROSC. Table 5 shows examples of piezo audio signal frequencies achieved at different ROSC resistor

values. Internal oscillator is factory trimmed to produce 3.435kHz frequency when using 121k

Ω ROSC resistor.

See note below the table 5.

Table 5. Self-drive mode oscillator resistor and output frequency examples

ROSC

[kΩ]

(E96 1%)

FAUDIO

[kHz]

412

1.0

280

1.5

210

2.0

165

2.5

140

3.0

133

3.1

127

3.3

121

3.4

118

3.5

105

4.0

Note: FAUDIO [kHz] = 415.6 / ROSC [k

Ω]