TLV2544Q, TLV2548Q, TLV2548M

3-V TO 5.5-V, 12-BIT, 200-KSPS, 4-/8-CHANNEL, LOW-POWER

SERIAL ANALOG-TO-DIGITAL CONVERTERS WITH AUTOPOWER-DOWN

SGLS119C – FEBRUARY 2002 – REVISED OCTOBER 2002

19

POST OFFICE BOX 655303

reference block equivalent circuit

INT REF

Close = Int Ref Used

Open = Ext Ref Used

REFM

Sample

Convert

~50 pF

CDAC

External to the Device

10

µF

Internal

Reference

Compensation

Cap

0.1

µF

Decoupling

Cap

REFP

NOTES: A. If internal reference is used, tie REFM to AGND and install a 10

µF (or 4.7 µF) internal reference compensation capacitor between

REFP and REFM to store the charge as shown in the figure above.

B. If external reference is used, the 10

µF (internal reference compensation) capacitor is optional. REFM can be connected to external

REFM or AGND.

C. Internal reference voltage drift, due to temperature variations, is approximately

±10 mV about the nominal 2 V (typically) from –10°C

to 100

°C . The nominal value also varies approximately ±50 mV across devices.

D. Internal reference leakage during low ON time: Leakage resistance is on the order of 100 M

Ω or more. This means the time constant

is about 1000 s with 10

µF compensation capacitance. Since the REF voltage does not vary much, the reference will come up quickly

after resuming from auto power down. At power up and power down the internal reference sees a glitch of about 500

µV when 2

V internal reference is used (1 mV when 4 V internal reference is used). This glitch settles out after about 50

µs.

power down

Writing 8000h to the device puts the device into a software power down state. For a hardware power-down, the

dedicated PWDN pin provides another way to power down the device asynchronously. These two power-down

modes power down the entire device including the built-in reference to save power. It requires 20 ms to resume

from either a software or hardware power down.

Auto power-down mode is always enabled. This mode maintains the built-in reference if an internal reference

is used so resumption is fast enough to be used between cycles.

The configuration register is not affected by any of the power down modes but the sweep operation sequence

has to be started over again. All FIFO contents are cleared by the power-down modes.