LTC3577-4_15 Datasheet, PDF (40/52 Pages) Linear Technology – Highly Integrated Portable Product PMIC

LTC3577-3/LTC3577-4
OPERATION
Table 10 shows the third byte of data that can be written
to at sub-address 0x02. This byte of data is referred to as
the “LED DAC register”. The LED current source utilizes a
6-bit 60dB exponential DAC. This DAC provides accurate
current control from 20μA to 20mA with approximately
1dB per step with I_LED(FS) programmed to 20mA. The LED
current can be approximated by the following equation:
I_LED
=
I_LED(FS)
•
⎛
10^⎝⎜
3
•
DAC –
63
63
⎞
⎠⎟
where DAC is the decimal value programmed into the I²C
“LED DAC register”. For example with I_LED(FS) = 20mA and
DAC[5:0] = 101010 (42 decimal) I_LED equates to 2mA.
Table 10. I²C LED DAC Register
LED DAC REGISTER
ADDRESS: 00010010
SUB-ADDRESS: 00000010
BIT NAME
FUNCTION
B0 DAC[0]
6-Bit Log DAC Code
B1 DAC[1]
B2 DAC[2]
B3 DAC[3]
B4 DAC[4]
B5 DAC[5]
B6 N/A
Not Used—No Effect On Operation
B7 N/A
Not Used—No Effect On Operation
Table 11 shows the final byte of data that can be written
to at sub-address 0x03. This byte of data is referred to as
the “LED PWM register”. See the “LED PWM vs Constant
Current Operation” section for detailed information on
how to set the values of this register.
Table 11. LED PWM Register
LED PWM REGISTER
ADDRESS: 00010010
SUB-ADDRESS: 00000011
BIT NAME
FUNCTION
B0 PWMDEN[0]
PWM DENOMINATOR
B1 PWMDEN[1]
B2 PWMDEN[2]
B3 PWMDEN[3]
B4 PWMNUM[0] PWM NUMERATOR
B5 PWMNUM[1]
B6 PWMNUM[2]
B7 PWMNUM[3]
40
I²C Output Data
One status byte may be read from the LTC3577-3/LTC3577-4
as shown in Table 12. A 1 read back in the any of the bit
positions indicates that the condition is true. For example,
1 read back from bit A3 indicate that LDO1 is enabled and
regulating correctly. A status read from the LTC3577-3/
LTC3577-4 captures the status information when the
LTC3577-3/LTC3577-4 acknowledge its read address.
Table 12. I²C READ Register
STATUS REGISTER
ADDRESS: 00010011
SUB-ADDRESS: None
BIT NAME
FUNCTION
A0 CHARGE
Charge Status (1 = Charging)
A1 STAT[0]
A2 STAT[1]
STAT[1:0]; 00 = No Fault
01 = TOO COLD/HOT
10 = BATTERY OVERTEMP
11 = BATTERY FAULT
A3 PGLDO[1]
LDO1 Power Good
A4 PGLDO[2]
LDO2 Power Good
A5 PGBCK[1]
Buck1 Power Good
A6 PGBCK[2]
Buck2 Power Good
A7 PGBCK[3]
Buck3 Power Good
Bit A7 shows the power good status of Buck3. A 1 indicates
that Buck3 is enabled and is regulating correctly. A 0 indi-
cates that either Buck3 is not enabled, or that the Buck3 is
enabled, but is out of regulation by more than 8%.
Bit A6 shows the power good status of Buck2. A 1 indicates
that Buck2 is enabled and is regulating correctly. A 0 indi-
cates that either Buck2 is not enabled, or that the Buck2 is
enabled, but is out of regulation by more than 8%.
Bit A5 shows the power good status of Buck1. A 1 indicates
that Buck1 is enabled and is regulating correctly. A 0 indi-
cates that either Buck1 is not enabled, or that the Buck1 is
enabled, but is out of regulation by more than 8%.
Bit A4 shows the power good status of LDO2. A 1 indicates
that LDO2 is enabled and is regulating correctly. A 0 indi-
cates that either LDO2 is not enabled, or that the LDO2 is
enabled, but is out of regulation by more than 8%.
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