AN837 Datasheet, PDF (1/3 Pages) Silicon Laboratories – How to Configure a Low-Power Timer/Oscillator to Operate from Higher Supply Voltages

AN837
How to Configure a Low-Power Timer/Oscillator to Operate from Higher
Supply Voltages
1. Introduction
Low-power, low voltage CMOS timers/oscillators like the TS3001/TS3002 are specified to operate at 1 V,
consuming supply currents as low as 1 µA. While the TS3001/TS3002 has an operating VDD voltage range of
0.9 V–1.8 V, systems running from higher supply voltages can also take advantage of the low supply currents of
this micropower timer, by adding a few inexpensive transistors to the operating circuit.
In the circuit below, Q2 drops the voltage from a higher V+ voltage to supply the TS3002 at a reduced voltage. The
VBE voltage of Q1 provides a compensating voltage for the VBE of Q2, providing some temperature tracking. The
values R1 and R2 can be changed to optimize the design for other V+ voltage ranges, as shown in Table 1.
Q3, together with R5, provide an output level translation function, so that the output voltage can swing to V+ if
needed. Q3 was chosen for its low output capacitance (specified at 3 pF with VDS = 15 V; estimated at 10 pF with
VDS = 3 V). The value of R5 can be decreased to increase positive-going slew rates, at the expense of current
drawn from V+. With R5=220 k, trise = 2.2 µs during the rising edge of FOUT.
V+
2.3V-3.3V
CR2032
coin
cell
C1
0.1µF
R1
1M
R2
1M
C2
1nF
Q1
2N3904
Q2
2N3904
FOUT
VDD
BOOST
RSET
TS3002
PWMOUT
GND
R4
4.32M
R3
CTRL
CSET
1M
R5
(optional- for
U1
C3A
C3B
220K
PWM output)
10pF
10pF
FOUT
Q3
½ CMRDM3590
R6
220K
PWMOUT
Q4
½ CMRDM3590
Figure 1. TS3002 Operating from a CR2032 Coin Cell
Rev. 1.0 1/15
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AN837