MAX1870AETJ+ Maxim Integrated Products, MAX1870AETJ+ Datasheet - Page 26

• Manufacturer Part Number: MAX1870AETJ+
• Description: Battery Management Li+ Step Up/Step Down Battery Charger
• Manufacturer: Maxim Integrated Products

Specifications of MAX1870AETJ+

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Step-Up/Step-Down
Li+ Battery Charger
LDO provides a 5.4V supply derived from DCIN and
delivers over 10mA. The n-channel MOSFET driver
DBST is powered by DLOV and can source 2.5A and
sink 5A. Since LDO provides power to the internal ana-
log circuitry, use an RC filter from LDO to DLOV as
shown in Figure 1 to minimize noise at LDO. LDO also
supplies the 4.096V reference (REF) and most of the
internal control circuitry. Bypass LDO with a 1µF or
greater capacitor to GND.
Figure 12. CCS Simplified Loop Diagram
Figure 13. CCI and CCS Loop Response
26
______________________________________________________________________________________
CCS
CLS
C
GMS
CS
100
-20
-40
80
60
40
20
0
CSS
0.1
R
OGMS
CCI LOOP RESPONSE
10
GM
PHASE
FREQUENCY (Hz)
PWM
A
CSS
MAG
1k
CSSP
CSSN/
CSSS
RS1_
100k
0
-45
-90
100
-20
-40
Table 4 lists the recommended components and refers
to the circuit of Figure 1. The following sections describe
how to select these components.
The MAX1870A requires one p-channel MOSFET and
one n-channel MOSFET. Component substitutions are
permissible as long as the on-resistance and gate
charge are equal or lower and the voltage, current, and
power-dissipation ratings are high enough. If using a
lower-power application, scale down the MOSFETs with
lower gate charge and the MOSFET’s on-resistance
can be scaled up. For example, in a system designed
to deliver half as much current, MOSFETs selected with
twice the on-resistance and half as much gate charge
ensure equal or better efficiency, and reduce size and
cost. If resistive losses dominate, it can be possible to
reduce the gate charge at the cost of on-resistance
and still achieve a similar efficiency.
Make sure that the linear regulators can drive the
selected MOSFETs. The average current required to
drive a given MOSFET is:
where f
80
60
40
20
0
0.1
switch
10
CCS LOOP RESPONSE
PHASE
is 400kHz (typ).
FREQUENCY (Hz)
Applications Information
I
I
LDO
VHN
1k
MAG
= Q
= Q
100k
gM2
gM1
Component Selection
x f
x f
10M
switch
switch
0
-45
-90
MOSFETs