4 (8)

DA1634.001

28 November, 2008

FUNCTIONAL DESCRIPTION

N

N

N

N Main Functions

MAS1634 has two functional blocks. First is the LED

driver

to drive LEDs in a wrist watch applications.

Second is Bias voltage generator for generating bias

current for the drivers

MAS1634 has two operating modes. These modes

are simply ON and OFF modes.

ON mode is selected when XPD is high. In ON

mode each of the four output drivers can be

switched on separately by setting each of the INx

control inputs high. If control input is low the

corresponding current output driver is off. If all

control inputs are low the bias generator is turned

off.

OFF mode is selected when XPD is low. In OFF

mode the bias generator and the current drivers are

in power down.

The device has two supply voltage pins VDD1 and

VDD2 and which are internally connected. It is

sufficient to connect only one of the two supply pins

but if both supplies are connected then they should

be connected to same voltage potential.

The device has also two supply ground pins GND1

and GND2 and which are internally connected. It is

sufficient to connect only one of the two ground pins

but if both grounds are connected then they should

be connected to same ground potential.

N

N

N

N Inverting input buffer

The inverting buffers buffer the input signals. These

blocks also contain pull-down resistors and they are

switched in an inactive high impedance state if the

XPD input is low.

If the XPD pin is high then the INx inputs have pull

down by the pull down resistors. Nominally the

values of the pull down resistors are 1.7 M

but

they can vary ±15%.

The XPD input doesn’t have pull down resistor so

this input must be driven by the controller or be

connected to VDD (always ON mode) in order to

achieve properly controlled operation.

N

N

N

N Output Driver

Four switchable low-voltage 2.1 mA constant current

sinks

with

very

low

drop-out

voltage

are

implemented to drive external VDD connected

LEDs.

N

N

N

N Bias Generator

Bias voltage generator supplies bias current for the

output drivers. It is turned on if XPD is high and if

any of the four control inputs is high.