Datasheet
LPC15XX All information provided in this document is subject to legal disclaimers. © NXP B.V. 2014. All rights reserved.
Product data sheet Rev. 1 — 19 February 2014 41 of 99
NXP Semiconductors
LPC15xx
32-bit ARM Cortex-M3 microcontroller
8.26.1 Features
• Seven selectable inputs. Fully configurable on either the positive side or the negative
input channel.
• 32-stage voltage ladder internal reference for selectable voltages on each
comparator; configurable on either positive or negative comparator input.
• Voltage ladder source voltage is selectable from an external pin or the 3.3 V analog
voltage supply.
• 0.9 V internal band gap reference voltage selectable as either positive or negative
input on each comparator.
• Temperature sensor voltage selectable as either positive or negative input on each
comparator.
• Voltage ladder can be separately powered down for applications only requiring the
comparator function.
• Individual comparator outputs can be connected internally to the SCT and ADC trigger
inputs or the external pins.
• Separate interrupt for each comparator.
• Pin filter included on each comparator output.
• Three propagation delay values are programmable to optimize between speed and
power consumption.
• Relaxation oscillator circuitry output for a 555 style timer operation using comparator
blocks 0 and 1.
8.27 Temperature sensor
The temperature sensor transducer uses an intrinsic pn-junction diode reference and
outputs a CTAT voltage (Complement To Absolute Temperature). The output voltage
varies inversely with device temperature with an absolute accuracy of better than ±5 C
over the full temperature range (40 C to +105 C). The temperature sensor is only
approximately linear with a slight curvature. The output voltage is measured over different
ranges of temperatures and fit with linear-least-square lines.
After power-up, the temperature sensor output must be allowed to settle to its stable value
before it can be used as an accurate ADC input.
For an accurate measurement of the temperature sensor by the ADC, the ADC must be
configured in single-channel burst mode. The last value of a nine-conversion (or more)
burst provides an accurate result.
8.28 Internal voltage reference
The internal voltage reference is an accurate 0.9 V and is the output of a low voltage band
gap circuit. A typical value at T
amb
= 25 C is 0.905 V. The internal voltage reference can
be used in the following applications:
• When the supply voltage V
DD
is known accurately, the internal voltage reference can
be used to reduce the offset error E
O
of the ADC code output. The ADC error
correction then increases the accuracy of temperature sensor voltage output
measurements.