SSM2537

Data Sheet

Rev. 0 | Page 14 of 16

PDM PATTERN CONTROL

The SSM2537 has a simple control mechanism that can set

the part for low power states and control functionality. This is

accomplished by sending a repeating 8-bit pattern to the device.

Different patterns set different functionality (see Table 8).

Any pattern must be repeated a minimum of 129 times. The

part is automatically muted when a pattern is detected so that

a pattern can be set while the part is operational without a

pop/click due to pattern transition.

All functionality set via patterns returns to its default values

after a clock-loss power-down.

Table 8. PDM Watermarking Pattern Control Descriptions

Pattern

Control Description

0xD2

Gain optimized for PVDD = 3.6 V operation.

0xD4

Gain optimized for PVDD = 2.5 V operation.

0xD8

Gain optimized for PVDD = 5 V operation.

0xE1

Ultralow EMI mode.

0xE2

Low latency mode with pattern delay (~15 μs latency).

0xE4

fS set to opposite value determined by GAIN_FS pin.

0xAA

Device reset: Place device into default configuration.

0x66

Mute.

0xAC

Power-down: All blocks off except for PDM interface.

Normal start-up time.

EMI NOISE

The SSM2537 uses a proprietary modulation and spread-

spectrum technology to minimize EMI emissions from the

device. For applications that have difficulty passing FCC

Class B emission tests, the SSM2537 includes a modulation

select mode (ultralow EMI emissions mode) that significantly

reduces the radiated emissions at the Class-D outputs, particu-

larly above 100 MHz. This mode is enabled by activating PDM

Watermarking Pattern 0xE1 (see Table 8).

PDM CHANNEL SELECTION

The SSM2537 includes a left/right input select pin, LRSEL

(see Table 9), that determines which of the time-multiplexed

input streams is routed to the amplifier. To select the left input

channel, connect LRSEL to PGND. To select the right channel,

connect LRSEL to VDD. At any point during amplifier

operation, the logic level applied to LRSEL may be changed

and the output will switch the input streams without audible

artifacts. No muting, watermarking pattern or synchronizing

are necessary to achieve a click/pop free LRSEL transition.

Table 9. LRSEL Pin Function Descriptions

Device Setting

LRSEL Pin Configuration

Right Channel Select

VDD

Left Channel Select

PGND

OUTPUT MODULATION DESCRIPTION

The SSM2537 uses three-level, Σ-Δ output modulation. Each

output can swing from PGND to PVDD and vice versa. Ideally,

when no input signal is present, the output differential voltage is

0 V because there is no need to generate a pulse. In a real-world

situation, there are always noise sources present.

Due to this constant presence of noise, a differential pulse

is generated, when required, in response to this stimulus. A

small amount of current flows into the inductive load when

the differential pulse is generated.

Most of the time, however, the output differential voltage is 0 V,

due to the Analog Devices, Inc., three-level, Σ-Δ output

modulation. This feature ensures that the current flowing

through the inductive load is small.

When the user wants to send an input signal, an output pulse

(OUT+ and OUT−) is generated to follow the input voltage.

The differential pulse density (VOUT) is increased by raising

the input signal level. Figure 33 depicts three-level, Σ-Δ output

modulation with and without input stimulus.

Figure 33. Three-Level, Σ-Δ Output Modulation With and Without Input Stimulus

OUTPUT > 0V

+5V

0V

OUT+

+5V

0V

OUT–

+5V

0V

VOUT

OUTPUT < 0V

+5V

0V

OUT+

+5V

0V

OUT–

0V

–5V

VOUT

OUTPUT = 0V

OUT+

+5V

0V

+5V

0V

OUT–

+5V

–5V

0V

VOUT