TS4604

Application information

Doc ID 17913 Rev 1

21/31

6.7

Performance of CMRR

When the TS4604 is used in differential mode (Figure 46), because of the resistor matching

the CMRR can have important variations.

To minimize these variations, we recommend using the same kind of resistor (same

tolerance).

The following equation is valid for frequencies ranging from DC to about kHz. The equation

is simplified by neglecting the

ΔR² terms. ΔR is the tolerance value as a percentage.

It is extremely important to correctly match the resistors to obtain a good CMRR.

All the tests have been performed with resistors with a tolerance value of 0.1%.

Example:

With

ΔR = 1% the minimum CMRR would be 34 dB.

With

ΔR = 0.1% the minimum CMRR would be 54 dB.

6.8

Internal and external undervoltage detection

The TS4604 embeds two UVLOs: one internal and one external.

6.8.1

Internal UVLO

The internal UVLO monitors the power supply via pins PVCC_HP (20) and PVCC_LD(23).

The threshold is set to 2.8 V with a 200 mV hysteresis. If the power supply decreases to

2.6 V, the TS4604 switches to standby mode. To switch the device on again, the power

supply voltage must increase to above 2.8 V.

Refer to Table 4 for the tolerance of the UVLO voltage.

6.8.2

External UVLO

The Ex_UVP pin (25) is an external undervoltage detection input that can be used to start

up or shutdown the TS4604 by applying the correct voltage value. A 1.25 V internal

precision voltage is used as a reference to monitor the voltage applied to the Ex_UPVP pin.

To set a desired shutdown threshold and hysteresis for the application, a resistor divider can

be calculated as follows.

with the condition R3>>R1//R2.

CMRR

20

100

4

ΔR

------------ 1

Rfd

Rin

----------

+

⎝⎠

⎛⎞ dB

()

log

⋅

≈

Vuvp

1.25V

R1

R2

+

()

R1

---------------------------

⋅

=

Vhyst

≈ 5μAR3

R2

R1

--------

1

+

⎝⎠

⎛⎞

⋅

⋅