Datasheet

Data Sheet ADP1649
Rev. 0 | Page 15 of 28
ANALOG-TO-DIGITAL CONVERTER OPERATION
The internal 4-bit analog-to-digital converter (ADC) is config-
urable to measure the LED V
F
, the integrated circuit (IC) die
temperature, or to measure an external voltage using the GPIO2
pin. Read the 4-bit resolution output code from Register 0x08
using the I
2
C interface.
Figure 34. Available ADC Modes
The ADC can perform the conversion immediately on an I
2
C
command or it can delay the conversion until the next time the
ADP1649 exits an active mode. Delayed conversion can be
useful, for example, for measuring the IC temperature at the
end of a timed flash period.
To set up a delayed conversion, set ADC_EN to the required
mode while OUTPUT_EN = 0. Next, set the ADP1649 to the
desired output mode (torch, flash assist light, or 5 V output) and
set OUTPUT_EN = 1. The ADC conversion is performed when
the ADP1649 exits the chosen mode.
To perform an immediate conversion, set ADC_EN to the
required mode during ADP1649 operation (OUTPUT_EN = 1).
Note that an ADC conversion cannot be performed when the
ADP1649 is idle. This is interpreted as an attempt to set up a
delayed conversion.
LED V
F
Mode
The ADC can measure the LED V
F
in both flash and assist/torch
modes. In torch mode, set ADC_EN = 01 to begin a conversion.
The value can be read back from the ADC_VAL[5:2] bits 1 ms
after the conversion has started. Assist/torch mode, rather than
flash mode, is best in the handset production test to verify the
LED V
F
.
Figure 35. ADC Timing for All Modes Except V
F
Measurement in Flash Mode
In flash mode, set ADC_EN = 01. The conversion occurs imme-
diately before the timeout; therefore, the FL_TIM bits set when
the ADC sample occurs. This allows the V
F
to settle from the
initial peak as the junction temperature of the LED stabilizes.
An LED temperature vs. flash time profile for the handset PCB
design can be generated during the design phase by varying the
FL_TIM bits from the lowest to the highest setting and collecting a
V
F
sample on each flash.
Figure 36. ADC Timing for V
F
Measurement in Flash Mode
Die Temperature Mode
The ADC measures the IC die temperature and provides the result
to the I
2
C interface. This is useful during the design phase of the
flash system to optimize PCB layout for the best thermal design.
Write ADC_EN = 10 to begin a die temperature measurement.
The value can be read back from the ADC_VAL[5:2] bits 1 ms
after the conversion has started. The most stable and accurate value
of the die temperature is available at the end of the flash pulse.
External Voltage Mode
The ADC measures the voltage on the GPIO2 pin when the GPIO2
is configured as an ADC input by setting IO2_CFG = 11. One
example is using an external temperature dependent resistor to
create a voltage based on the temperature of the flash LED. The
EN line can be used for biasing to reduce leakage current when
the flash is not being used.
5 V OUTPUT OPERATION
The ADP1649 can be used as a 5 V boost to supply up to 500 mA
for an audio voltage rail or keypad LED driver voltage. To move
into voltage regulation mode, the OUTPUT_EN bit must be set
to 0. To enable the 5 V output, set LED_MOD[1:0] = 01, and set
OUTPUT_EN = 1. The ADP1649 sets the VOUT pin to 5 V
and disconnects VOUT from LED_OUT. The VOUT pin is
connected to the SW node when the ADP1649 is not enabled.
Do not connect VOUT directly to a positive external voltage
source because this causes current to flow from VOUT to the
battery.
INTERFACE/
CONTROL
LED_OUT
SDA
SCL
ADC_EN[1:0]
4-BIT ADC
IC TEMPERATURE
SENSOR
EN
GPIO2
ADC_VAL[5:2]
PTC
10779-034
REG 0x08, ADC_EN = 01
START CONVERSION
(INTERNAL SIGNAL)
1
m
s
ADC_VAL[5:2]
AVAILABLE FOR READ
I
2
C DATA BUS
10779-035
LED CURRENT
REG 0x02, FL_TIM = XXXX ms
REG 0x03, I_FL = XXXXX mA
REG 0x04, OUTPUT_EN = 1
STR_LV = 0
LED_MOD = 11
I
2
C DATA BUS
0A
STROBE
FL_TIM
START CONVERSION
(INTERNAL SIGNAL)
ADC_VAL[5:2]
AVAILABLE FOR READ
REG 0x08, ADC_EN = 01
t
S
= 1ms
10779-036
I
FLASH