MAX1687EUE-T Maxim Integrated Products, MAX1687EUE-T Datasheet - Page 7

• Manufacturer Part Number: MAX1687EUE-T
• Description: DC/DC Switching Controllers StepUp w/Prec Adapt Crnt Limit for GSM
• Manufacturer: Maxim Integrated Products

When starting up, the MAX1687/MAX1688 employ four
successive phases of operation to reduce the inrush of
current from the battery. These phases are Linear
Regulator Mode, Pseudo Buck Mode, Pseudo Boost
Mode, and Boost Mode. In Linear Mode, the output
connects to the input through a 30Ω precharge PMOS
device (Figure1, Q1). The transition from Linear Mode
to Pseudo Buck Mode occurs when V
The transition from Pseudo Buck Mode to Pseudo
Boost Mode occurs when V
sition from Pseudo Boost Mode to Boost Mode occurs
when V
battery input current remains relatively constant, and
V
Figure 1. Functional Diagram
OUT
V
( ) ARE FOR MAX1687
[ ] ARE FOR MAX1688 (ALSO DASHED LINES)
IN
[CHG]
ON
(LIM)
changes slope as it rises.
OUT
> V
IN
_______________________________________________________________________________________
. Due to these mode changes, the
Precise, Adaptive Current Limit for GSM
g
m
g
m
OUT
= V
LX1
MAX1687
MAX1688
IN
OUT
- 0.7V. The tran-
Step-Up DC-DC Converters with
INDUCTOR-
CURRENT
TROUGH
DETECT
ZERO
CROSSING
PEAK/
TIMER
= V
IN
- 3V.
V
PRECHARGE
INDUCTOR-CURRENT
CONTROL LOGIC
HYSTERETIC
CONSTANT
Logic circuits in the MAX1687/MAX1688 control the
inductor ripple current to typically 200mA (Figure 2).
The voltage at LIM (CHG) programs I
tor current oscillates between I
I
When ON goes low, the device enters Standby Mode,
inductor current ramps to zero, and the output discon-
nects from the input. If ON remains low for greater than
1.2ms (typ), the device shuts down and quiescent cur-
rent drops to 3µA (typ).
PEAK
Q1
P-SWITCH
.
V
IN
Hysteretic Inductor-Current Control
N-SWITCH
V
LX2
Q3
OUT
V
IN
- V
DIODE
Q2
P-SWITCH
REF
Standby/Shutdown
PEAK
FB
PEAK
- 200mA and
. The induc-
V
OUT
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