RT1650 datasheet(18/26 Pages) RICHTEK

18 / 26 page

RT1650

is a registered trademark of Richtek Technology Corporation.

www.richtek.com

DS1650-00

July

2015

Figure 8. Equivalent Resistance for Temperature

Sensing

Figure 9. Thermal Sensing Voltage

Communication

The RT1650 supports two communication modulations,

Amplitude Shift Keying (ASK), Frequency Shift Keying

(FSK), to communicate with the power transmitter. For

ASK modulation, the RT1650 provides two integrated

communication N-FETs which are connected to the

COM1 and COM2 pins. These N-FETs are used for

modulating the secondary load current which allows the

RT1650

communicate

Control

Error

and

configuration information to the transmitter. Figure 10

shows the RT1650 operating with capacitive load

modulation. When the N-FETs are turned-on, there is

effectively a capacitor connected between AC1 and

AC2. The impedance seen by the coil will be reflected

in the primary as a change in current.

Coil

Ccom

COM1

COM2

AC1

AC2

Figure 10. Capacitive Load Modulation

The RT1650 supports FSK demodulation to receive the

power signal from the transmitter shown as Figure 11.

The change in frequency between high and low states

is dependent on the operating frequency. The power

transmitter should modulate the power signal at

specific times during the Negotiation phase to avoid

interrupting communication packets from the receiver.

The FSK modulation scheme should be compliant with

WPC Volume II V0.9.

Figure 11. FSK Modulation Power Signal

Bit Encoding Scheme

According to WPC protocol, the RT1650 uses a

differential bi-phase encoding scheme to modulate

data bits onto the Power Signal. The internal clock

signal has a frequency 2kHz. The Receiver shall

encode a ONE bit using two transitions in the Power

Signal, such that the first transition coincides with the

rising edge of the clock signal, and the second

transition coincides with the falling edge of the clock

signal. The Receiver shall encode a ZERO bit using a

single transition in the Power Signal, which coincides

with the rising edge of the clock signal. Figure 12

shows an example of the differential bi-phase encoding.

-50

-25

100

125

150

Temperature (degree-C)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

-50

-25

100

125

150

Temperature (°C)

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