Sensors
NXP Semiconductors 19
MMA26xx
3.3 Voltage Regulators
The device derives its internal supply voltage from the HCAP supply voltage. The device includes separate internal voltage
regulators for the analog (V
REGA
) and digital circuitry (V
REG
). External filter capacitors are required, as shown in Figure 1.
The voltage regulator module includes voltage monitoring circuitry which holds the device in reset following power-on until the
HCAP and internal voltages have stabilized sufficiently for proper operation. The voltage monitor asserts internal reset when the
HCAP supply or internally regulated voltages fall below predetermined levels. A reference generator provides a stable voltage
which is used by the ΣΔ converter.
Figure 10. Voltage Regulation and Monitoring
3.3.1 C
REG
and C
REGA
Regulator Capacitor
The internal regulator requires an external capacitor between the C
REG
pin and V
SS
pin, and the C
REGA
pin and V
SSA
pin for
stability. Figure 1 shows the recommended types and values for each of these capacitors.
3.3.2 V
HCAP
Voltage Monitor
The device includes a circuit to monitor the voltage on the HCAP pin. If the voltage falls below the specified threshold in
Section 2, the device will be reset within the reset delay time (t
HCAP_POR
) specified in Section 2.7.
C
REGA
C
REG
HCAP
VOLTAGE
REGULATOR
REFERENCE
GENERATOR
V
REGA
= 2.50 V
DIGITAL
LOGIC
DSP
OTP
ARRAY
OSCILLATOR
ΣΔ
CONVERTER
BIAS
GENERATOR
TRIM
TRIM
V
REF_MOD
= 1.250 V
V
REG
= 2.50 V
BANDGAP
REFERENCE
V
BUF
V
REF
V
REGA
POR
V
REF
COMPARATOR
COMPARATOR
HCAP
COMPARATOR
V
REGA
V
REG
VOLTAGE
REGULATOR
Analog Filter Delay
t
VREG_POR
Analog Filter Delay
t
VREG_POR
Digital Delay
t
HCAP_POR
VOLTAGE
REGULATOR
V
BUF
