Document Number: 002-14886 Rev. *C

Page 4 of 24

CYW20737L

1. Functional Description

1.1 External Reset

External reset timing for the CYW20737L is illustrated in Figure 2.

Figure 2. External Reset Timing

1.2 32.768 kHz Oscillator

The CYW20737L includes a standard Pierce oscillator. The oscillator circuit includes a comparator with hysteresis on the output to

create a single-ended digital output. The hysteresis eliminates chatter when the input is near the comparator threshold (~100 mV).

The oscillator circuit can is designed for a 32 kHz or 32.768 kHz crystal oscillator, and can also be driven by an external clock input

with a similar frequency. Characteristics for a 32 kHz oscillator are defined in Table 2.

1.3 External DC-DC Switcher Characteristics

The CYW20737L requires an external 1.2V DC switcher to operate its internal digital and RF circuits. A suitable low-power, low-noise

switcher must be supplied for proper circuit operation. Digital and analog I/Os, as well as the internal EEPROM operation from the

VBAT/VDDIO, can be from 1.62V to 3.63V. The recommended setting is 3V nominal voltage.

The following switcher, from Torex Semiconductor LTD, has been qualified and is recommended for all designs.

Table 2. 32 kHz Crystal Oscillator Characteristics

Parameter

Symbol

Conditions

Min.

Typ.

Max.

Unit

Output frequency

–

–

32.768

–

kHz

Frequency tolerance

Crystal-dependent

–

100

–

ppm

Start-up time

––

–

500

µs

Crystal drive level

For crystal selection

0.5

–

–

µW

Crystal series resistance

For crystal selection

–

–

70

kΩ

Crystal shunt capacitance

For crystal selection

–

–

1.3

pF

RESET_N

Pulse width

>20 µs

Crystal Enable

Baseband Reset

Start reading EEPROM and 

firmware boot

Crystal 

warm‐up 

delay: 

~ 5 ms