LM3S5D91 Datasheet, PDF (1060/1340 Pages) Texas Instruments – Stellaris® LM3S5D91 Microcontroller

Analog Comparators
In each range, the internal reference, V_IREF, has 16 pre-programmed thresholds or step values. The
threshold to be used to compare the external input voltage against is selected using the VREF field
in the ACREFCTL register.
In the high-range mode, the V_IREF threshold voltages start at the ideal high-range starting voltage
of V_DDA/3.875 and increase in ideal constant voltage steps of V_DDA/31.
In the low-range mode, the V_IREF threshold voltages start at:0V and increase in ideal constant voltage
steps of V_DDA/23. The ideal V_IREF step voltages for each mode and their dependence on the RNG
and VREF fields are summarized in Table 19-3 on page 1060.
Table 19-3. Internal Reference Voltage and ACREFCTL Field Values
ACREFCTL Register
EN Bit
Value
RNG Bit Value ^{Output Reference Voltage Based on VREF Field Value}
EN=0
RNG=X
0 V (GND) for any value of VREF. It is recommended that RNG=1 and VREF=0 to minimize noise
on the reference ground.
RNG=0 Total resistance in ladder is 31 R.
VIREF = VDDA × ^RVREF
VIREF
V^VI^IR^RE^EF^F
=
=⁼
VDDA
V^VDDD^DA^A
×
×^×
RV^RR^TEF
R_(VV_RRR_TE_EF_F
RT
+ 8)
EN=1
RNG=1
TTohte^VVVV_VVVV^VV_VVVV^VV_VVVVV^VVV_alr^I_I^I_I^I_IIII^III_III^II_IIII^IIIar^RRR_RRRRRRRRR^RRRRR_RRRR^RRR_enEEE^EEE_EEEEEEs^EEEEE_EEEE^EEEgi^FFF_FFFFFFFFF^FFFFFFFF_FFFFsetaonf⁼⁼⁼⁼₌⁼⁼₌₌₌₌⁼⁼⁼_=======⁼⁼_=cinete^VV_VVVV^VVVV_VVVVVV^VVV000_000000inrn^DDD_D^D_D^D_D^D_D^D_DD^DD_DDDD^..._{......laaDDDDD}^DDDD_D^DD_DDDD^DDD888₈₈₈₁₁₁ld_AAAAA^AAAA_A^AAAAA_AAAArd₄₄₄⁵⁵⁵₅₅₅eef^{××××}_{××××××}^××_{××××}^×××e_333r r⁺⁺⁺_+++ise^V_VVVV^RRR_RRR^RRR((((_{(×××}n2^VVVV_Vc⁰⁰⁰₀₀₀^R_RRRR3^VVVVVV_VVV^R_R^RRRRR₂₂₂₂e^RRRR_RVVV^RRRRRR_RRR^..._...R^E_EEEE^TT_T^TTTTTT₃₃₃₃i^EEEEEE_EEE^EEEE_En_RRR.¹¹¹₁₁₁^F_FFFF^FFFFFF_FFF³³³³₃₃^FFFF_Ft_EEEh⁰⁰⁰₀₀₀¹¹¹¹₁₁i_FFFs⁶⁶⁶₆₆₆⁺⁺⁺⁺₊mo^×××_×××⁸⁸⁸⁸₈de^VVV_VVV⁾⁾⁾⁾₎is^RRR_RRR0^EEE_EEE.8^FFF_FFF5-2.448 V.
VIREF = V0D.D1A4×3 ^V×^R2V^E3R^FEF
VIREF = 0.143 ײV³REF
VIREF = 0.143 × VREF
19.4
The range of internal reference for this mode is 0-2.152 V.
Initialization and Configuration
The following example shows how to configure an analog comparator to read back its output value
from an internal register.
1060
Texas Instruments-Production Data
January 22, 2012