AAT2805 Datasheet, PDF (12/17 Pages) Advanced Analogic Technologies – Dual High Efficiency Charge Pump for White LED and Flash Applications

AAT2805
Dual High Efficiency Charge Pump
for White LED and Flash Applications
AS²Cwire Serial Interface
The AS²Cwire single wire interface is used to set the
possible combinations of current levels and LED
channel states. AS²Cwire has addressing capability
for multiple data registers. With multiple data regis-
ters, the main and sub-channel can be programmed
together or independently from one another.
AS²Cwire relies on the number of rising edges of the
EN/SET pin to address and load the registers.
AS²Cwire latches data or address after the EN/SET
pin has been held high for time T_LAT. 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 2⁴ or 16, so that
Address 1 is signified by 17 rising edges, Address 2
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 particular address, followed by a
pause with EN/SET held high for the T_LAT timeout
period, a burst of rising edges signifying data, and a
T_LAT timeout for the data registers. Once an address
is set, then multiple writes to the corresponding data
register are allowed.
When EN/SET is held low for an amount of time
greater than T_OFF, the charge pump enters into shut-
down mode and draws less than 1µA from the sup-
ply. Address 1 is the default address on the first ris-
ing edge after the charge pump has been disabled.
Whenever shutdown mode is entered, all registers
are reset to 1.
AS²Cwire Addressing
Five addresses are available to enable all of the
part's functionality (see Table 3). Two 4-bit registers
control the main and sub-channel, giving 16 settings
for each. The main and sub-channel are pro-
grammed to the same constant current level by using
Address 1. Use Addresses 2 and 3 to program the
main and sub-channel independently. Use Address 4
to program the Max Current register, which sets the
Max Current scale. Lastly, Address 5 programs the
Low Current register. The Low Current register con-
trols the efficient Low Current mode.
When the Max Current register is programmed to 1,
2, or 3, changing the data for Addresses 1-3 will
result in the corresponding values found in Table 1.
When the Max Current register is programmed to 4,
the part is programmed to operate in Low Current
mode and the Data for Addresses 1-3 is irrelevant. In
Low Current mode, the Low Current register takes
precedence. See the Low Current Register Settings
table below for the current level settings and main/
sub-configurations that result.
Address
1
2
3
4
5
EN/SET
Edges
17
18
19
20
21
Addressed
Register
1&2: D1-D4 Current
1: D1-D3 Current
2: D4 Current
3: Max Current
4: Low Current
Table 3: Address Settings.
Max Current and Low Current Registers
Use the Max Current and Low Current registers to
program constant current settings outside of the
20mA Max scale. By default (without changing the
Max Current register), the charge pump operates in
the 20mA Max scale (see Table 1). For example, to
change to the 30mA Max scale, address the Max
Current register with 20 rising edges and pause for
T_LAT. Program the Max Current register with 2 rising
edges and pause for T_LAT. The part will next operate
in the same Data row, but for the setting found in the
30mA Max column. Next, to change to a different
setting on the 30mA Max scale, address the D1-D4
register with 17 rising edges. Program the new con-
stant current level with 1-16 rising edges. The part will
update to the new Data setting as shown in Table 1.
The charge pump has a distinct Low Current mode
with ultra-low quiescent current. For drive currents of
2mA or less, the part operates with significantly
reduced quiescent current. This is particularly useful
for applications requiring an "always on" condition
such as transmissive displays. For another example,
to change to Low Current mode, address the Max
Current register with 20 rising edges and pause for
T_LAT. Program the Max Current register with 4 rising
edges and pause for _TLAT. Address the Low Current
register with 21 rising edges and pause for T_LAT.
Program the Low Current register with 1-16 rising
edges. The part will update to the new Low Current
mode setting and operate with significantly reduced
quiescent current.
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2805.2005.05.1.2