ADT7470: disable pulse stretching in LF-PWM mode

Hi Risto,

Pulse stretching is disabled by disabling the tach measurements on the ADT7470 i.e.writing a 1 to bits 3, 2,1 and 0 of the tach register 0x74.

Pulse stretching is also disabled by enabling high frequency fan drive mode i.e. writing a 0 to Bit 6 of register 0x40.

Rgds,

Joe.

Hi Joe,

thank you for your answer.

I tried to disable the tach measurement by writing 0x7F to the Register 0x74 in LF Mode.

But, unfortunately pulse stretching is still enabled.

I tried it on the EVAL-ADT7470EBZ Evaluation Board and also on my application board. -> Same result.

Unfortunately HF Mode is not an option for my application.

Any ideas ?

Hi Risto,

Can you send me a list of the register settings that you are using for the ADT7470 and we will look at this in the lab.

How are you verifying that pulse stretching is enabled?

Thanks,

Joe.

From: Risto analog@sgaur.hosted.jivesoftware.com

Sent: 16 January 2012 18:42

To: Towey, Joe

Subject: New message: "ADT7470: disable pulse stretching in LF-PWM mode"

Analog Devices EngineerZone<http://ez.analog.com/index.jspa>

ADT7470: disable pulse stretching in LF-PWM mode

reply from Risto<http://ez.analog.com/people/Risto> in Temperature Sensors - View the full discussion<http://ez.analog.com/message/40395#40395

Hi Joe,

jtowey wrote:

Can you send me a list of the register settings that you are using for the ADT7470 and we will look at this in the lab.

for register contents see attached file: stretch.sav

You may open the file in the ADT7470 Evaluation Software [V 1.0.0] or view it with your favorite text editor.

jtowey schrieb:

How are you verifying that pulse stretching is enabled?

See attached file stretching.pdf for oscilloscope pictures.

The stretch is also audible: Fans continuously speeds up and down.

Risto

Hi Risto,

Pulse stretching is only disabled when HF mode is selected (bit[6] of 0x40 = 0).  Pulse stretching is enabled in LF mode as you correctly observed. However there is no workaround to disable pulse stretching in LF mode as this was designed as a feature for use with 3 or 4 wire fans running in LF mode. Apologies for any confusion previously.

Best Regards,

Joe.