Rev. 1.0 1/15

Copyright © 2015 by Silicon Laboratories

AN837

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.

Figure 1. TS3002 Operating from a CR2032 Coin Cell

R2

1M

R1

1M

C1

0.1µF

V+

2.3V-3.3V

Q1

2N3904

Q2

2N3904

Q3

½ CMRDM3590

FOUT

PWMOUT

R6

220K

R5

220K

TS3002

R3

1M

R4

4.32M

C3B

10pF

FOUT

BOOST

PWMOUT

CTRL

CSET

GND

RSET

VDD

U1

CR2032

coin

cell

C2

1nF

C3A

10pF

Q4

½ CMRDM3590

(optional- for

PWM output)