EPC635 datasheet(30/97 Pages) EPC

30 / 97 page

5.5. LED driver

The LED driver has two different outputs LED and LED2.

The LED output is an open-drain MOSFET device. It can sink up to 500mA peak current during operation. The modulation signal is a

square-wave up to typically 20MHz with a duty cycle of 50% which depends on the mode of operation.

IMPORTANT: There are non-modulating DC modes (e.g. grayscale with LED/LD illumination) which keeps the LED driver always turned

on. In this case, the user has to take care that LED driver and the epc635 chip does not exceed the maximum operating limits.

The LED2 output is a digital push-pull driver output.

The LED_driver register contains several static bit fields that can be used for setting drive strength, polarity, etc. depending on the external

LED/LD circuitry used in the application (see chapter 8.7.6.). These bit fields must not be modified during the frame acquisition.

■ led2_en bit enables the LED2 push-pull driver. LED and LED2 must not be simultaneously used. When LED2 is used, LED can be

turned off by led_drv_en = 0

■ The led_drv_sel bits set LED driver output maximum current e.g. for 200mA to 100% , 64%, 46% or 33%. Refer to chapter 8.7.6,

LED_driver.

■ The led_on bit permanently turns on the LED/LD (torch function). Keep care to the power dissipations if you operate the LEDs and laser

diodes in this mode.

■ The led_drv_en bit enables the internal LED driver circuits. The enabled after reset (default), can be disabled if there will be no frame ac-

quisition for a long time.

■ The led_inv_en bit sets the polarity of the LED driver (inverts LED and LED2 pin). This must be set/cleared with respect to external

LED/LD driver circuit topology and stored in the EEPROM. It is cleared after reset (default), which matches to the simple external LED

circuit shown in Figure 14.

■ led_ssr_en bit sets a slower slew rate for the LED driver (part of the LED driver transistor is switched on with a delay to lower the current

peaks).

5.6. DLL (Delay Locked Loop)

The LED driver and the LEDs/LDs may shift the phase depending of temperature, ageing, etc.. The deviations are from seconds up to sev -

eral minutes and longer and impact the performance of the distance accuracy. The built-in DLL circuit minimizes this behaviour by com -

pensating the delay of the critical signals. It is located between the modulator and the LED driver (see Figure 26). LED pin is used only in

this description for simplification. Nevertheless, the explanation is valid for both LED and LED2 output.

LED Driver

Modulator

led_fb

∆

Phase

Detector

x-Delay

160x60

Pixel Field

mga_ref

mga

led_mod

m-Clk

Delay

n-Clk

Delay

epc635

mgx_delay_sel

dist_offset

led_preheat_en

led_drv_en

led_inv_en

Demodulator

DLL

dll_bypass

dll_fb_pol

ext_mod_clk

mod_clk_sel

pll_clk

dll_ctrl_ext

VSSLED

LED

LEDFB

led_drv_sel

led_on

VDDLED

led_ssr_en

led2_en

LED2

mod_clk

ext_mod_clk

mod_clk_sel

mod_clk

ext_mod_clk

mod_clk_sel

mod_clk_div

Figure 26: Simplified modulator, demodulator, DLL and LED driver diagram

The modulator invokes the DLL before DCS frame acquisition at the rate set by the DLL_measurement_rate register (see Figure 27,

tSYNCH). This stimulates the mga demodulation signal. After passing digital delay stages, it is distributed to the pixels in the pixel-field (Figure

26, red path, point A). The same time, the led_mod signal passes the DLL, the LED driver, the LED pin until it comes to the LED circuit

(blue path, point B) which generates the modulated IR light. The DLL compares the demodulation signal phase coming from the pixel

(point A) with the feedback signal (LEDFB pin) the LED circuit (point B). The distance reading error is minimal if the delays on the signals

from points A and B are identical. The DLL minimizes deviations by adding a certain delay on the led_mod signal (x-Delay).

Characteristics subject to change without notice

30 / 97

Datasheet_epc635-V1.02

EPC635 数据表(PDF) 30 Page - Espros Photonics corp

EPC635 数据表(HTML) 30 Page - Espros Photonics corp

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97

数据表下载

链接网址

EPC635 数据表(PDF) 30 Page - Espros Photonics corp

EPC635 数据表(HTML) 30 Page - Espros Photonics corp

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97

数据表 下载

链接网址

数据表下载