DA6251.002
27 October, 2017
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)
HIGH
LOW 1)
HIGH
OFF
ON
ON
ON
OFF
OFF
OFF
OFF
OFF 2)
OFF 2)
ON
OFF
ON
OFF
ON 3)
OFF
SHUTDOWN
LED
LOW 1)
HIGH
OFF
ON
PIEZO
HIGH
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 400kΩ 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
COUT
CS
10F
100nF
470pF
1.5M
RB
RF
200k
Note: the voltage ripple at VOUT output is approximately proportional to ratio of piezo load capacitance (CLOAD) and
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 [MΩ]
VOUT [V]
200
150
162
274
-
4.3
3.6
4.7
10
-
9
10
12
15
17.5
Note: VOUT=VFB*(1+R2/R1), VFB=0.4V
10 (21)
MAS [ MICRO ANALOG SYSTEMS ]
