AAT1235 Analogic Corporation, AAT1235 Datasheet - Page 11

• Manufacturer Part Number: AAT1235
• Manufacturer: Analogic Corporation

Constant Current Output Level Settings
and AS
The LED current sink level of each group and the
on/off status of each channel is controlled by
AnalogicTech's AS
each current sink is programmable, no PWM or
additional control circuitry is needed to control LED
brightness. This feature greatly reduces the burden
on a microcontroller or system IC to manage LED
or display brightness, allowing the user to "set it
and forget it." With its high-speed serial interface
(1MHz data rate), the input sink current can be
changed quickly and easily. Also the non-pulsating
LED current reduces system noise and improves
LED reliability.
AS
the EN/SET pin to address and load the registers.
AS
pin has been held high for time T
Address or data is differentiated by the number of
EN/SET rising edges. Since the data registers are
4 bits each, the differentiating number of pulses is
2
edges, Address 1 by 18 rising edges, and so forth.
Data is set to any number of rising edges between
1 and including 16. A typical write protocol is a
burst of EN/SET rising edges, signifying a particu-
lar address, followed by a pause with EN/SET held
high for the T
edges signifying data, and a T
data registers. Once an address is set, then multi-
ple writes to that address are allowed where only
data is issued. When EN/SET is held low for an
amount of time longer than T
AAT1235 enters into shutdown mode and draws
less than 1µA from the input. Data and Address
registers are cleared (reset to 0) during shutdown.
1235.2007.01.1.0
Table 1: AS
4
or 16, so that Address 0 is signified by 17 rising
Address
2
2
Cwire relies on the number of rising edges of
Cwire latches data or address after the EN/SET
0
1
2
3
4
2
Cwire Serial Interface
2
Cwire Serial Interface Addressing.
LAT
Rising Edges
timeout period, a burst of rising
2
EN/SET
Cwire serial digital input. Since
17
18
19
20
21
LAT
OFF
A1-A3, B1-B2 on
B1-B2 current
A1-A3 current
timeout for the
B1-B2 on/off
A1-A3 on/off
Register
(500µs), the
LAT
Data
(500µs).
High Efficiency White LED Drivers
Address 0 and 1: LED Brightness Control
Outputs A1, A2, A3, B1, B2 are each capable of
sinking up to 30mA. The maximum current can be
programmed by an external resistor at the RSET
pin. It is suggested to connect up to four white
LEDs in series for each channel and to keep the
same number of LEDs in each channel.
Outputs B1 and B2 are intended to drive the white
LEDs for the backlight in a phone, while A1:A3 can
supply the keypad LEDs. For large displays, all five
outputs can be used.
Address 2: LED Group B ON/OFF
Control
Table 2: Address 0 and 1 for Current Setting as
Table 3: Address 2 for Group B ON/OFF State.
Percentage of the Maximum Level Set by R
Data
1
2
3
4
Data
10
12
13
14
15
16
11
1
2
3
4
5
6
7
8
9
for Backlight and Keypad
B1
Off
Off
On
On
All Outputs (%)
13.5
12.0
10.5
100
9.0
84
71
60
51
43
35
31
26
21
18
15
B2
Off
On
Off
On
SET
11
.