Datasheet

ADP1650
Rev. C | Page 15 of 32
PROGRAMMABLE BATTERY DC CURRENT LIMIT
The ADP1650 has four optional programmable input dc current
limits that limit the maximum battery current that can be taken
over all conditions. This allows higher LED currents to be used
in a system with significant variation in LED forward voltage
(V
F
) and supply battery voltage without risk of the current
allocated to the flash being exceeded.
Table 8. Input DC Current Limit Setting the LED Current
Bit Name Current Limit
IL_DC 00 = 1.5 A
01 = 1.75 A
10 = 2.0 A (default)
11 = 2.25 A
During startup of the flash, if the battery current does not reach
the dc current limit, the LED current is set to the current value
of the I_FL bits. If the battery current does hit the programmed
dc current limit on startup, the LED current does not increase
further. The dc current limit flag is set in the fault information
register. The I_FL bits in Register 0x03 are set to the actual LED
current and are available for readback.
REG 0x02, FL_TIM = XXXX ms
REG 0x03, I_FL = XXXXX mA
IL_DC_EN = 1
IL_DC = XX A
I
2
C DATA BUS
STROBE
ADP1650 SETS OUTPUT_EN TO 0.
ADP1650 SETS LED_MOD TO 00.
NO LIMIT LED CURRENT
ACTUAL LED CURRENT
ADP1650 SETS FL_IDC (REG 0x05) TO 1.
ADP1650 SETS I_FL TO ACTUAL LED CURRENT.
REG 0x04, OUTPUT_EN = 1
STR_LV = 1
LED_MOD = 11
08837-013
Figure 35. DC Current Limit Operation in a Low Battery, High LED V
F
Case
The camera system shown in Figure 36 can adjust the image
sensor settings based on the known reduced LED current for a
low battery and a high V
F
LED.
SELECT FLASH CURRENT
SELECT MAX BATTERY CURRENT
PREFLASH STROBE
DC LIMIT HIT?
LED CURRENT =
PROGAMMED LED
CURRENT
NO
LED CURRENT =
REDUCED LED CURRENT
YES
BATTERY CURRENT =
PROGRAMMED DC LIMIT
I
2
C READ LED CURRENT
ADJUST IMAGE SENSOR
STROBE
STROBE
08837-014
Figure 36. Use of the DC Current Limit in an Optimized Camera System
ANALOG-TO-DIGITAL CONVERTER OPERATION
The internal 4-bit analog-to-digital converter (ADC) is configura-
ble to measure the LED V
F
, integrated circuit (IC) die temperature,
or an external voltage using the GPIO2 pin. Read the 4-bit
resolution output code back from Register 0x08 using the I
2
C
interface.
INTERFACE/
CONTROL
LED_OUT
SDA
SCL
ADC_EN[1:0]
4-BIT ADC
IC TEMPERATURE
SENSOR
EN
GPIO2
ADC_VAL[5:2]
PTC
08837-015
Figure 37. Available ADC Modes in the ADP1650
The ADC can perform the conversion either immediately on an
I
2
C command, or it can delay the conversion until the next time
the ADP1650 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. Then
set the ADP1650 to the desired output mode (torch, flash assist
light, or 5 V output) and set OUTPUT_EN = 1. The ADC conver-
sion is performed when the ADP1650 exits the chosen mode.
To perform an immediate conversion, set ADC_EN to the
required mode during ADP1650 operation (OUTPUT_EN = 1).
Note that an ADC conversion cannot be performed when the
ADP1650 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
.
REG 0x08, ADC_EN = 01
START CONVERSION
(INTERNAL SIGNAL)
1
m
s
ADC_VAL[5:2]
AVAILABLE FOR READ
I
2
C DATA BUS
08837-016
Figure 38. ADC Timing for All Modes Except V
F
Measurement in Flash Mode
In flash mode, set ADC_EN = 01. The conversion happens just
before the timeout occurs; therefore, the FL_TIM bits set when
the ADC sample occurs. This allows the V
F
to settle from the