ADP1660ACBZ-R7 datasheet(13/28 Pages) AD

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Data Sheet

ADP1660

Rev. 0 | Page 13 of 28

INDEPENDENT TRIGGER MODES

When the LED_MOD bits are set to 100 or 101, the ADP1660

allows for independent triggering of each LED at a current level

between the configured flash currents and TxMASK currents.

In independent trigger mode, the STROBE pin controls LED1,

and the GPIO pin controls LED2 (see Figure 24).

•

When the STROBE or GPIO pin goes high, the current

produced at the LED1 or LED2 pin is at the level specified

by the I_FL1 bits (Register 0x06) or the I_FL2 bits

(Register 0x09), respectively.

•

When the STROBE or GPIO pin goes low, the current

produced at the LED1 or LED2 pin is at the level specified

by the I_TX1 bits (Register 0x07) or the I_TX2 bits

(Register 0x0A), respectively.

LED1 CURRENT

I_TX1

I_FL1

STROBE

LED2 CURRENT

I_TX2

I_FL2

GPIO

Figure 24. Independent Trigger Mode

When the LED_MOD bits are set to 100, the flash timer is used.

If both LEDs are on for a combined time that is equal to the value

specified by the FL_TIM bits (both outputs OR’ed), the ADP1660

sets both LED_ENx bits to 0 and sets LED_MOD to 000.

The independent trigger modes (LED_MOD bits set to 100 or

101) present a possible overtemperature risk; careful evaluation

of their implementation must be performed. Before enabling either

independent trigger mode, contact your local Analog Devices

Field Applications Engineer for assistance.

FIXED 5 V OUTPUT MODE

When the LED_MOD bits are set to 001, the ADP1660 allows

VOUT to be regulated to 5 V. In this mode, the total output current

must be kept below 500 mA. Enabling one or both LEDs allows

low levels of current to the LEDs.

In fixed 5 V output mode, the VOUT pin is connected to the SW

node when the ADP1660 is not enabled. Do not connect VOUT

directly to a positive external voltage source; doing so causes

current to flow from VOUT to the battery. Changing the mode

to standby (LED_MOD = 000) ends voltage regulation; VOUT

returns to a value that is approximately the same as VIN.

FREQUENCY FOLDBACK

The optional frequency foldback feature optimizes efficiency

by reducing the switching frequency to 1.5 MHz when the value

of VIN is slightly less than the value of VOUT. To enable frequency

foldback, set the FREQ_FB bit to 1 in Register 0x03.

LOW BATTERY LED CURRENT FOLDBACK

As the battery discharges, the lower battery voltage results in

higher peak currents through the battery ESR, which may cause

early shutdown of other devices on the battery. The ADP1660

includes an optional low battery detection feature, which reduces

the flash current to a value from 0 mA to 750 mA when the battery

voltage falls below a programmable level. The low battery current

level can be set from 0 mA to 750 mA using the I_VB_LO bits

(Bits[5:0]) in Register 0x05.

To enable low battery detection and to specify the voltage at

which this detection becomes active, set the V_VB_LO bits

(Bits[2:0]) in Register 0x04 (see Table 8).

Table 8. VDD Level for Low Battery Detection

V_VB_LO Bit Value

VDD Level for Low Battery Detection (V)

000

Low battery detection disabled (default)

001

3.3

010

3.35

011

3.4

100

3.45

101

3.5

110

3.55

111

3.6

If a low battery fault is detected within a programmed window of

detection, the lower current is latched for the remainder of the

flash. The window size is specified by the V_BATT_WINDOW

bits (Bits[4:3]) in Register 0x04 (see Table 9).

Table 9. Low Battery Detection Window Size

V_BATT_WINDOW

Bit Value

Window Size (ms)

Window disabled; low battery detection

is enabled for the entire flash period

5 (default)

By reducing the window size to the beginning of the flash only,

the user can reduce the chance of partial exposure of the picture

in the case that the image sensor is using a rolling scan. If a global

scan is used, it is recommended that the low battery detection

window be disabled, thereby providing low voltage protection

throughout the flash time.

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