Datasheet

Integrated Charger, Dual Main Step-Down
Controllers, and Dual LDO Regulators
MAX17085B
20 _____________________________________________________________________________________
Detailed Description
The MAX17085B integrated charger and main step-
down controllers are ideal for notebook applications
where board space and solution cost are key require-
ments. Together with the integrated, always-on 100mA
LDO5 and 50mA LDO3, the MAX17085B provides a
complete power solution for the notebook in the off-state,
standby-state, and full active state. A functional diagram
of the MAX17085B is shown in Figure 2.
Charger
The MAX17085B uses a new thermally optimized high-
frequency architecture that reduces the output capaci-
tance and inductance, resulting in smaller PCB area
and lower cost. The MAX17085B charger includes all
the necessary functions to charge Li+, NiMH, and NiCd
batteries. An all n-channel synchronous-rectified step-
down DC-DC converter is used to implement a precision
constant-current, constant-voltage charger. The charge
current and input current-limit sense amplifiers have low-
input offset errors (200FV typ), allowing the use of small-
valued sense resistors.
Main SMPS
The 5V and 3.3V main SMPSs in the MAX17085B use
Maxim’s Quick-PWM pulse-width modulator, specifically
designed for handling fast load steps while maintaining
a relatively constant operating frequency and inductor
operating point over a wide range of input voltages. The
Quick-PWM architecture circumvents the poor load-tran-
sient timing problems of fixed-frequency current-mode
PWMs while also avoiding the problems caused by widely
varying switching frequencies in conventional constant-
on-time and constant-off-time PWM schemes.
100mA 5V Linear Regulator (LDO5)
and Bias Supply (VCC)
The MAX17085B includes a high-current (100mA),
always-on fixed 5V linear regulator (LDO5). LDO5 is
required to generate the 5V bias supply necessary to
power up the switching regulators, and as the input
supply to the 3.3V linear regulator (LDO3). Once the 5V
switching regulator (SMPS5) is enabled and in regula-
tion, LDO5 is bypassed by an internal switch from OUT5
to LDO5. After switchover, the LDO5 pin can source
200mA. LDO5 starts up as soon as DCIN has valid volt-
age (around 2.5V), and regulates to ~ 4.5V using an
internal crude reference. REF starts at the same time,
and once REF is in regulation, LDO5 switches over to
use the accurate REF, and regulates up to 5V.
The MAX17085B requires a low-noise 5V bias supply
(V
CC
) for its internal circuitry. Typically, this 5V bias is
supplied by LDO5 through a lowpass filter. The total sup-
ply current required for the MAX17085B is:
I
BIAS(MAX)
= I
CC(MAX)
+ f
SW5
Q
G5
+ f
SW3
Q
G3
+
f
SWC
Q
GC
≈ 45mA to 90mA (typ)
50mA, 3.3V Linear Regulator (LDO3)
A lower current (50mA), always-on fixed 3.3V linear regu-
lator, is also included in the MAX17085B. Once the 3.3V
switching regulator (SMPS3) is enabled and in regula-
tion, LDO3 is bypassed by an internal switch from OUT3
to LDO3. After switchover, the LDO3 pin can source
more than 200mA. LDO3 starts up as soon as REF is in
regulation. This limits the inrush current by sequencing
LDO5 to start before LDO3.
Table 2. Component Suppliers
SUPPLIER WEBSITE
AVX Corp. www.avxcorp.com
Central
Semiconductor Corp.
www.centralsemi.com
Fairchild
Semiconductor
www.fairchildsemi.com
International Rectifier www.irf.com
KEMET Corp. www.kemet.com
NEC/TOKIN America www.nec-tokinamerica.com
Panasonic Corp. www.panasonic.com/industrial
Philips/nxp
Semiconductor
www.semiconductors.philips.com
Pulse Engineering www.pulseeng.com
SUPPLIER WEBSITE
Renesas Technology
Corp.
www.renesas.com
SANYO Electric
Co., Ltd.
www.sanyodevice.com
Sumida Corp. www.sumida.com
Taiyo Yuden www.t-yuden.com
TDK Corp. www.component.tdk.com
TOKO America, Inc. www.tokoam.com
Vishay (Dale, Siliconix) www.vishay.com
Würth Elektronik
GmbH & Co. KG
www.we-online.com