ADP3405 Analog Devices, ADP3405 Datasheet - Page 12

• Manufacturer Part Number: ADP3405
• Description: GSM Power Management System
• Manufacturer: Analog Devices

ADP3405
For the lowest ripple and best efficiency, use a 0.1 µF, ceramic
capacitor for the charge pump flying capacitor (CAP+ and CAP–).
A good quality dielectric, such as X7R is recommended.
Setting the Charger Turn-On Threshold
The ADP3405 can be turned on when the charger input exceeds
a programmable threshold voltage. The charger’s threshold and
hysteresis are set by selecting the values for R1 and R2 shown in
Figure 2.
The turn-on threshold for the charger is calculated using:
Where V
CHRON hysteresis resistance.
The hysteresis is determined using:
Combining the above equations and solving for R1 and R2 gives
the following formulas:
T
is the CHRON threshold voltage and R
V
CHR
R
2
=
=




V



R



V
R
R
HYS
1 =
V
CHR
2
2
T
+
×
R
=
R
R
V
R
HYS
−
R
HYS
HYS
T
1
V
1
HYS
×

 ×

T
R
×
0.006 (0.15)
0.002 (0.05)
×
V
HYS
R
PIN 1
SEATING
× 1
R
HYS
HYS
PLANE
R
1

 +

28
−
28-Lead Thin Shrink Small Outline (TSSOP)
1
1
R




1
0.0256 (0.65)
×
V
BSC
T
HYS
Dimensions shown in inches and (mm).
0.386 (9.80)
0.378 (9.60)
OUTLINE DIMENSIONS
is the
0.0118 (0.30)
0.0075 (0.19)
(RU-28)
0.0433 (1.10)
14
15
0.0035 (0.090)
MAX
0.0079 (0.20)
Example: R1 = 10 kΩ and R2 = 30.2 kΩ gives a charger thresh-
old (not counting the drop in the power Schottky diode) of
3.5 V ± 160 mV with a 200 mV ± 30 mV hysteresis.
Charger Diode Selection
The diode shown in Figure 2 is used to prevent the battery from
discharging into the charger turn-on setting resistors, R1 and R2.
A Schottky diode is recommended to minimize the voltage differ-
ence from the charger to the battery and the power dissipation.
Choose a diode with a current rating high enough to handle both
the battery charging current and the current the ADP3405 will
draw if powered up during charging. The battery charging current
is dependent on the battery chemistry and the charger circuit.
The ADP3405 current will be dependent on the loading.
Printed Circuit Board Layout Considerations
Use the following general guidelines when designing printed
circuit boards:
1. Split the battery connection to the VBAT and SIMBAT
2. SIM input and output capacitors should be returned to the
3. VCCA and VTCXO capacitors should be returned to AGND.
4. VCC and VRTC capacitors should be returned to DGND.
5. Split the ground connections. Use separate traces or planes
0.177 (4.50)
0.169 (4.30)
pins of the ADP3405. Use separate traces for each connection
and locate the input capacitors as close to the pins as possible.
SIMGND and kept as close as possible to the ADP3405 to
minimize noise. Traces to the SIM charge pump capacitor
should be kept as short as possible to minimize noise.
for the analog, digital, and power grounds, and tie them
together at a single point, preferably close to the battery return.
0.256 (6.50)
0.246 (6.25)
8
0
0.028 (0.70)
0.020 (0.50)