COMP — Comparator

The comparator (COMP) compares an input voltage (VIN+) against a second input voltage (VIN-). VIN+ can be derived from an analog input pin (AIN0-AIN7). VIN- can be derived from multiple sources depending on the operation mode of the comparator.

Main features of the comparator are:

Input range from 0 V to VDD
Single-ended mode
- Fully flexible hysteresis using a 64-level reference ladder
Differential mode
- Configurable 50 mV hysteresis
Reference inputs (VREF):
- VDD
- External reference from AIN0 to AIN7 (between 0 V and VDD)
- Internal references 1.2 V, 1.8 V and 2.4 V
Three speed/power consumption modes: low-power, normal and high-speed
Single-pin capacitive sensor support
Event generation on output changes
- UP event on VIN- > VIN+
- DOWN event on VIN- < VIN+
- CROSS event on VIN+ and VIN- crossing
- READY event on core and internal reference (if used) ready

Figure 1. Comparator overview

Once enabled (using the ENABLE register), the comparator is started by triggering the START task and stopped by triggering the STOP task. After a start-up time of t_COMP,START, the comparator will generate a READY event to indicate that it is ready for use and that its output is correct. When the COMP module is started, events will be generated every time VIN+ crosses VIN-.

Operation modes

The comparator can be configured to operate in two main operation modes, differential mode and single-ended mode. See the MODE register for more information. In both operation modes, the comparator can operate in different speed and power consumption modes (low-power, normal and high-speed). High-speed mode will consume more power compared to low-power mode, and low-power mode will result in slower response time compared to high-speed mode.

Use the PSEL register to select any of the AIN0-AIN7 pins as VIN+ input, irregardless of the operation mode selected for the comparator. The source of VIN- depends on which operation mode is used:

Differential mode: Derived directly from AIN0 to AIN7
Single-ended mode: Derived from VREF. VREF can be derived from VDD, AIN0-AIN7 or internal 1.2 V, 1.8 V and 2.4 V references.

The selected analog pins will be acquired by the comparator once it is enabled.

An optional hysteresis on VIN+ and VIN- can be enabled when the module is used in differential mode through the HYST register. In single-ended mode, VUP and VDOWN thresholds can be set to implement a hysteresis using the reference ladder (see Figure 4). This hysteresis is in the order of magnitude of 50 mV, and shall prevent noise on the signal to create unwanted events. See Figure 5 for illustration of the effect of an active hysteresis on a noisy input signal.

An upward crossing will generate an UP event and a downward crossing will generate a DOWN event. The CROSS event will be generated every time there is a crossing, independent of direction.

The immediate value of the comparator can be sampled to RESULT register by triggering the SAMPLE task.

Differential mode

In differential mode, the reference input VIN- is derived directly from one of the AINx pins.

Before enabling the comparator via the ENABLE register, the following registers must be configured for the differential mode:

Figure 2. Comparator in differential mode

Restriction: Depending on the device, not all the analog inputs may be available for each MUX. See definitions for PSEL and EXTREFSEL for more information about which analog pins are available on a particular device.

When HYST register is turned on while in this mode, the output of the comparator (and associated events) will change from ABOVE to BELOW whenever VIN+ becomes lower than VIN- - (V_DIFFHYST / 2). It will also change from BELOW to ABOVE whenever VIN+ becomes higher than VIN- + (V_DIFFHYST / 2). This behavior is illustrated in Figure 3.

Figure 3. Hysteresis enabled in differential mode

Single-ended mode

In single-ended mode, VIN- is derived from the reference ladder.

Before enabling the comparator via the ENABLE register, the following registers must be configured for the single-ended mode:

The reference ladder uses the reference voltage (VREF) to derive two new voltage references, VUP and VDOWN. VUP and VDOWN are configured using THUP and THDOWN respectively in the TH register. VREF can be derived from any of the available reference sources, configured using the EXTREFSEL and REFSEL registers as illustrated in Figure 4. When AREF is selected in the REFSEL register, the EXTREFSEL register is used to select one of the AIN0-AIN7 analog input pins as reference input. The selected analog pins will be acquired by the comparator once it is enabled.

Figure 4. Comparator in single-ended mode

When the comparator core detects that VIN+ > VIN-, i.e. ABOVE as per the RESULT register, VIN- will switch to VDOWN. When VIN+ falls below VIN- again, VIN- will be switched back to VUP. By specifying VUP larger than VDOWN, a hysteresis can be generated as illustrated in Figure 5 and Figure 6.

Writing to HYST has no effect in single-ended mode, and the content of this register is ignored.

Figure 5. Hysteresis example where VIN+ starts below VUP

Figure 6. Hysteresis example where VIN+ starts above VUP

Registers

Table 1. Instances
Base address	Peripheral	Instance	Description	Configuration
0x40013000	COMP	COMP	General purpose comparator

Table 2. Register Overview
Register	Offset	Description
TASKS_START	0x000	Start comparator
TASKS_STOP	0x004	Stop comparator
TASKS_SAMPLE	0x008	Sample comparator value
EVENTS_READY	0x100	COMP is ready and output is valid
EVENTS_DOWN	0x104	Downward crossing
EVENTS_UP	0x108	Upward crossing
EVENTS_CROSS	0x10C	Downward or upward crossing
SHORTS	0x200	Shortcut register
INTEN	0x300	Enable or disable interrupt
INTENSET	0x304	Enable interrupt
INTENCLR	0x308	Disable interrupt
RESULT	0x400	Compare result
ENABLE	0x500	COMP enable
PSEL	0x504	Pin select
REFSEL	0x508	Reference source select for single-ended mode
EXTREFSEL	0x50C	External reference select
TH	0x530	Threshold configuration for hysteresis unit
MODE	0x534	Mode configuration
HYST	0x538	Comparator hysteresis enable
ISOURCE	0x53C	Current source select on analog input

SHORTS

Address offset: 0x200

Shortcut register

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id																															E	D	C	B	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	READY_SAMPLE										Shortcut between READY event and SAMPLE task See EVENTS_READY and TASKS_SAMPLE
			Disabled	0								Disable shortcut
			Enabled	1								Enable shortcut
B	RW	READY_STOP										Shortcut between READY event and STOP task See EVENTS_READY and TASKS_STOP
			Disabled	0								Disable shortcut
			Enabled	1								Enable shortcut
C	RW	DOWN_STOP										Shortcut between DOWN event and STOP task See EVENTS_DOWN and TASKS_STOP
			Disabled	0								Disable shortcut
			Enabled	1								Enable shortcut
D	RW	UP_STOP										Shortcut between UP event and STOP task See EVENTS_UP and TASKS_STOP
			Disabled	0								Disable shortcut
			Enabled	1								Enable shortcut
E	RW	CROSS_STOP										Shortcut between CROSS event and STOP task See EVENTS_CROSS and TASKS_STOP
			Disabled	0								Disable shortcut
			Enabled	1								Enable shortcut

INTEN

Address offset: 0x300

Enable or disable interrupt

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id																																D	C	B	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	READY										Enable or disable interrupt for READY event See EVENTS_READY
			Disabled	0								Disable
			Enabled	1								Enable
B	RW	DOWN										Enable or disable interrupt for DOWN event See EVENTS_DOWN
			Disabled	0								Disable
			Enabled	1								Enable
C	RW	UP										Enable or disable interrupt for UP event See EVENTS_UP
			Disabled	0								Disable
			Enabled	1								Enable
D	RW	CROSS										Enable or disable interrupt for CROSS event See EVENTS_CROSS
			Disabled	0								Disable
			Enabled	1								Enable

INTENSET

Address offset: 0x304

Enable interrupt

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id																																D	C	B	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	READY										Write '1' to Enable interrupt for READY event See EVENTS_READY
			Set	1								Enable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
B	RW	DOWN										Write '1' to Enable interrupt for DOWN event See EVENTS_DOWN
			Set	1								Enable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
C	RW	UP										Write '1' to Enable interrupt for UP event See EVENTS_UP
			Set	1								Enable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
D	RW	CROSS										Write '1' to Enable interrupt for CROSS event See EVENTS_CROSS
			Set	1								Enable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled

INTENCLR

Address offset: 0x308

Disable interrupt

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id																																D	C	B	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	READY										Write '1' to Disable interrupt for READY event See EVENTS_READY
			Clear	1								Disable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
B	RW	DOWN										Write '1' to Disable interrupt for DOWN event See EVENTS_DOWN
			Clear	1								Disable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
C	RW	UP										Write '1' to Disable interrupt for UP event See EVENTS_UP
			Clear	1								Disable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
D	RW	CROSS										Write '1' to Disable interrupt for CROSS event See EVENTS_CROSS
			Clear	1								Disable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled

RESULT

Address offset: 0x400

Compare result

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	R	RESULT										Result of last compare. Decision point SAMPLE task.
			Below	0								Input voltage is below the threshold (VIN+ < VIN-)
			Above	1								Input voltage is above the threshold (VIN+ > VIN-)

ENABLE

Address offset: 0x500

COMP enable

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id																																		A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	ENABLE										Enable or disable COMP
			Disabled	0								Disable
			Enabled	2								Enable

PSEL

Address offset: 0x504

Pin select

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id																																	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	PSEL										Analog pin select
			AnalogInput0	0								AIN0 selected as analog input
			AnalogInput1	1								AIN1 selected as analog input
			AnalogInput2	2								AIN2 selected as analog input
			AnalogInput3	3								AIN3 selected as analog input
			AnalogInput4	4								AIN4 selected as analog input
			AnalogInput5	5								AIN5 selected as analog input
			AnalogInput6	6								AIN6 selected as analog input
			AnalogInput7	7								AIN7 selected as analog input

REFSEL

Address offset: 0x508

Reference source select for single-ended mode

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id																																	A	A	A
Reset 0x00000004				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	REFSEL										Reference select
			Int1V2	0								VREF = internal 1.2 V reference (VDD >= 1.7 V)
			Int1V8	1								VREF = internal 1.8 V reference (VDD >= VREF + 0.2 V)
			Int2V4	2								VREF = internal 2.4 V reference (VDD >= VREF + 0.2 V)
			VDD	4								VREF = VDD
			ARef	7								VREF = AREF (VDD >= VREF >= AREFMIN)

EXTREFSEL

Address offset: 0x50C

External reference select

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id																																	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	EXTREFSEL										External analog reference select
			AnalogReference0	0								Use AIN0 as external analog reference
			AnalogReference1	1								Use AIN1 as external analog reference
			AnalogReference2	2								Use AIN2 as external analog reference
			AnalogReference3	3								Use AIN3 as external analog reference
			AnalogReference4	4								Use AIN4 as external analog reference
			AnalogReference5	5								Use AIN5 as external analog reference
			AnalogReference6	6								Use AIN6 as external analog reference
			AnalogReference7	7								Use AIN7 as external analog reference

TH

Address offset: 0x530

Threshold configuration for hysteresis unit

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id																						B	B	B	B	B	B			A	A	A	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	THDOWN		[63:0]								VDOWN = (THDOWN+1)/64*VREF
B	RW	THUP		[63:0]								VUP = (THUP+1)/64*VREF

MODE

Address offset: 0x534

Mode configuration

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id																											B							A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	SP										Speed and power modes
			Low	0								Low-power mode
			Normal	1								Normal mode
			High	2								High-speed mode
B	RW	MAIN										Main operation modes
			SE	0								Single-ended mode
			Diff	1								Differential mode

HYST

Address offset: 0x538

Comparator hysteresis enable

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	HYST										Comparator hysteresis
			NoHyst	0								Comparator hysteresis disabled
			Hyst50mV	1								Comparator hysteresis enabled

ISOURCE

Address offset: 0x53C

Current source select on analog input

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id																																		A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	ISOURCE										Comparator hysteresis
			Off	0								Current source disabled
			Ien2mA5	1								Current source enabled (+/- 2.5 uA)
			Ien5mA	2								Current source enabled (+/- 5 uA)
			Ien10mA	3								Current source enabled (+/- 10 uA)

Electrical specification

COMP Electrical Specification

Symbol	Description	Min.	Typ.	Max.	Units
I_COMP,LP	Core run current in low power mode		2		µA
I_COMP,N	Core run current in normal mode		5		µA
I_COMP,HS	Core run current in high-speed mode		10		µA
t_PROPDLY,LP	Propagation delay, low-power mode^{^a}		0.6		µS
t_PROPDLY,N	Propagation delay, normal mode^{^a}		0.2		µS
t_PROPDLY,HS	Propagation delay, high-speed mode^{^a}		0.1		µS
V_DIFFHYST	Optional hysteresis applied to differential input		30		mV
V_VDD-VREF	Required difference between VDD and a selected VREF, VDD > VREF	0.3			V
I_{INT_REF}	Current used by the internal bandgap reference when selected as source for VREF		13		µA
t_{INT_REF,START}	Startup time for the internal bandgap reference		50	80	µS
E_{INT_REF}	Internal bandgap reference error	-3		3	%
R_LADDER	Reference ladder resistance, I_LADDER = VREF / R_LADDER		550		kΩ
V_INPUTOFFSET	Input offset	-10		10	mV
D_NLLADDER	Differential non-linearity of reference ladder		<0.1		LSB
t_COMP,START	Startup time for the comparator core		3		µS

Total comparator run current must be calculated from the I_COMP, I_{INT_REF}, and I_LADDER values for a given reference voltage.

^a Propagation delay is with 10 mV overdrive.