Rainbow Electronics MAX1706 - Manual (Page 17)

MAX1705/MAX1706
1- to 3-Cell, High-Current, Low-Noise,
Step-Up DC-DC Converters with Linear Regulator
______________________________________________________________________________________ 17
Implementing Soft-Start
To implement soft-start, set CLK/SEL low on power-up;
this forces PFM operation and reduces the peak switch-
ing current to 435mA. Once the circuit is in regulation,
CLK/SEL can be set high for full-power operation.
Adding a Manual Power Reset
A momentary pushbutton switch can be used to turn
the MAX1705/MAX1706 on and off (Figure 10). ONA is
pulled low and ONB is pulled high to turn the part off.
When the momentary switch is pressed, ONB is pulled
low and the regulator turns on. The switch must be
pressed long enough for the microcontroller (µC) to exit
reset (200ms) and drive ONA high. A small capacitor is
added to help debounce the switch. The µC issues a
logic high to ONA, which holds the part on regardless
of the switch state. To turn the regulator off, press the
switch again, allowing the µC to read the switch status
and pull ONA low. When the switch is released, ONB is
pulled high.
___________________Chip Information
TRANSISTOR COUNT: 1649
SUBSTRATE CONNECTED TO GND
MAX1705
2 NiCd/NiMH 2.4 3.3 730
2 NiCd/NiMH 2.4 5.0 500
3 NiCd/NiMH or 1 Li-Ion 3.6 5.0 850
MAX1706
450
350
550
Table 5. Typical Available Output Current
µ C
V
DD
I/O
MAX1705
MAX1706
ONA
ONB OUT
I/O
0.1 µ F
ON/OFF
270k
270k
Figure 10. Momentary Pushbutton On/Off Switch
MAX1705
MAX1706
PA
RF
LX POUT
GND LDO
CONTROL
INPUTS
µ
C
I/O
Figure 9. Typical Phone Application
1 NiCd/NiMH 1.2 3.3 300 200
NUMBER OF CELLS
INPUT VOLTAGE
(V)
STEP-UP OUTPUT VOLTAGE:
(PA POWER SUPPLY)
(V)
TOTAL OUTPUT CURRENT
(mA)