Silicon Chip – July 2019

64 Silicon chip Australia’s electronics magazine siliconchip.com.au

extra features. The heart of the unit is
still the AD584 (IC1). The “KH” ver-
sion of the AD584 is being used in this
module – the one with performance
specifications about twice as tight as
those of the “JH” version.
All of the circuitry at the top and
far left in Fig.5 is associated with the
unit’s battery power operation. The
Li-ion cell is charged via IC2 at up-
per left, using power from a 5V USB
source fed in via CON1. IC2 is a Linear
Technology LTC4054 charge control-
ler, with pin 3 connected to the posi-
tive pole of the cell.
The resistor connected from pin 5 of
IC2 (PROG) to ground sets the charging
current level, while pin 1 of the device
(CHRG) goes low when charging is tak-

ing place. It’s used to indicate when

the battery is being charged, via LED1.

The circuitry at centre and lower

left is intended to protect the Li-ion

battery from damage from overcharg-

ing or over-discharge. IC4 is a DW01-P

“Li-ion protector” chip which moni-

tors the battery voltage via its Vcc pin

(pin 5) and controls battery charging

and discharging via pins 3 (CGO) and

1 (DGO), connected to the gates of Q8,

an FS8205A dual N-channel power

Mosfet.

However, oddly, in the modules

we’ve seen, the sources and drains

of Q8 are shorted together by solder

blobs, disabling the protection cir-

cuitry by permanently connecting the

negative side of the battery directly to

ground. Perhaps this has been done

because the LTC4054 has its own pro-

tection circuitry, which may well be

sufficient for this application.

IC3 and its associated circuitry

at upper right is the boost convert-

er which steps up the Li-ion battery

voltage to around 13.5V, to run IC1.

It’s a standard configuration using

the MC34063A switchmode convert-

er chip. Mosfet Q1 is used as an on/

off switch for the boost converter, and

hence for IC1 as well.

It’s controlled in turn by IC5, shown

at lower centre, which is an unmarked

microcontroller unit (MCU) in an 8-pin

SOIC package. The MCU is also used

to perform the output voltage switch-

ing of IC1, as well as the indication

Fig.5: the circuit of the KKmoon voltage reference module is substantially more complicated, since it includes a DC/DC
converter to boost the Li-ion battery voltage to a suitable level as well as battery protection, a battery charger and output
voltage selection via pushbutton S1.