RT9535
High Efficiency Switching Mode Battery Charger
General Description
The RT9535 is a PWM switch mode battery charger
controller to fast charge single or multiple Li-Ion, NiMH
and NiCd batteries, using constant current or constant
voltage control. Maximum current can be easily
programmed by external resistor. The constant voltage
output can support up to 22V with 0.5% accuracy.
A third control loop limits the input current drawing from
the adapter during charging. This allows simultaneous
operation of the equipment and fast battery charging
without over loading to the adapter.
The RT9535 can charge batteries from 2.5V to 22V
with dropout voltage as low as 0.4V. A logic output
indicates Li-Ion full charge when current drops to 17%
of the full-scale programmed charge current.
Features
Fast Charging for Li-Ion, NiMH and NiCd Batteries
Adjustable Battery Voltages from 2.5V to 22V
High Efficiency : Up to 95%
Charging Current Programmed by Resistor
Precision 0.5% Charging Voltage Accuracy
Provide 5% Charging Current Accuracy
Input Current Limit Maximizes Charging Rate
500kHz Switching Frequency
Flag Indicates Li-Ion Charge Completion
Auto Shutdown with Adapter Removal
Only 10A Battery Reverse Current when Idle
Applications
Notebook Computers
Portable Instruments
Chargers for Li-lon, NiMH, NiCd and Lead Acid
Rechargeable Batteries
The RT9535 is available in the WQFN-24L 4x4
package.
Simplified Application Circuit
M1
V
IN
C
IN
R1
C1
R2
C2
ACN
ACP
ACDRV
EN
VIN
BOOT
ISET
VC
R4
C3
R5
C5
C4
VFB
SS
VFB
SGND
FBR
VHH
C6
GND
(Exposed Pad)
PGND
SNSH
SNSL
BATT
STATUS
C9
C11
RF1
To FBR Pin
C8
SW
D1
RS3
RS2
RF2
To VFB Pin
L1
RS1
V
BATT
C
BATT
RT9535
HSD
D2
V5V
R9
NTC
R
NTC
R10
C7
D3
To VHH Pin
RS4
R3
FBR
VHH
Copyright © 2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS9535-04
February 2016
www.richtek.com
1
RT9535
Ordering Information
RT9535
Package Type
QW : WQFN-24L 4x4 (W-Type)
(Exposed Pad-Option 1)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
Marking Information
1J=YM
DNN
1J= : Product Code
YMDNN : Date Code
RoHS compliant and compatible with the current
requirements of IPC/JEDEC J-STD-020.
Suitable for use in SnPb or Pb-free soldering processes.
Pin Configurations
(TOP VIEW)
GND
V5V
VIN
BOOT
HSD
HSD
24 23 22 21 20 19
ACN
ACP
ACDRV
EN
SS
ISET
1
2
3
4
5
6
7
8
9 10 11 12
18
17
16
15
25
14
13
GND
SW
SW
PGND
SNSH
SNSL
BATT
Copyright © 2016 Richtek Technology Corporation. All rights reserved.
VC
STATUS
NTC
FBR
VFB
VHH
WQFN-24L 4x4
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
DS9535-04
February 2016
RT9535
Functional Pin Description
Pin No.
1
2
3
4
5
6
7
8
9
10
11
Pin Name
ACN
ACP
ACDRV
EN
SS
ISET
VC
STATUS
NTC
FBR
VFB
Pin Function
Negative Terminal to Sense Input Current. A filter is needed to filter out the
500kHz switching noise.
Positive Terminal to Sense Input Current.
Drive Signal for the Gate of Input Power PFET.
Enable Control Input (Active High). It must be connected to a logical voltage or
pulled up to VIN with a 100k resistor.
Soft-Start Control Input. SS controls the soft-start time. Connect a capacitor
from SS pin to GND to set the soft-start time.
Charge Current Setting and System Loop Compensation Pin. Connect a
resistor from this pin to ground to set the charge current.
Control Signal of the Inner Loop of the Current Mode PWM. A capacitor of at
least 0.1F with a serial resistor to GND filters out the current ripple.
Flag to Indicate Charge Completion. It turns to logical high when the charge
current drops blew 17% of the setting charge current. A 0.1F capacitor from
STATUS to ground is needed to filter the sampled charge current ripple.
Input for an external NTC thermistor for battery temperature monitoring.
Negative Terminal of External Resistor Divider for Battery Voltage Feedback.
Battery Voltage Feedback. Using an external resistor divider to set battery full
charge voltage.
To supply the current sense amplifier CA for very low dropout condition. It must
be connected as shown in the typical application circuit or connected to VIN if
VIN is always larger than BATT by at least 1.8V.
Battery Voltage Sensing Input. A 10F or larger X5R ceramic capacitor is
recommended for filtering charge current ripple and stability purpose.
Negative Terminal for Sensing Charge Current.
Positive Terminal for Sensing Charge Current.
Power Ground.
Switch Node. This pin switches between ground and VIN with high dv/dt rates.
Care needs to be taken in the PCB layout to keep this node from coupling to
other sensitive nodes.
Drain of Internal High-Side power N-MOSFET Switch. Connect a low ESR
capacitor of 10F or higher from this pin to ground for good bypass.
Bootstrap Supply for the High-Side Power Switch Gate Driver and Control
Circuitry. In normal operation, V
BOOT
≈ V
SW
+ 5V.
Input Power Supply. Connect a low ESR capacitor of 10F or higher from this
pin to ground for good bypass.
Output of Internal 5V LDO. Connect a 1F ceramic capacitor from this pin to
GND for stability.
Analog Ground. Layout input capacitor and V5V capacitor to this pin as close
as possible.
Exposed Pad. Connect the exposed pad to GND.
12
VHH
13
14
15
16
17, 18
19, 20
21
22
23
24
25
(Exposed Pad)
BATT
SNSL
SNSH
PGND
SW
HSD
BOOT
VIN
V5V
GND
GND
Copyright © 2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS9535-04
February 2016
www.richtek.com
3
RT9535
Function Block Diagram
NTC
ACDRV
VIN
ACN
R
1
200k
EN
5V
0.5
μ
A
SD
UVLO
VIN
BATT
+
1.4V
C3
THERMISTOR
5V
REFERENCE
DRIVER
VIN
LDO
C2
UVLO
3.9V
I
VA
STATUS
I
CHG
5
OSCILLATOR
R
2
CA
I
CHG
PWM
C1
HSD
S
R
SW
BOOT
V5V
V
REF
2.5V
0.4V
GND
VHH
I
CHG
SLOP COMP
SNSH
SNSL
VFB
FBR
SD
100mV
+
I
VA
V
REF
2.5V
VA
V
REF
2.5V
EA
1.3V
I
CL
CL
Soft-Start
COUNTER
ACP
ACN
ISET
SS
VC
PGND
Copyright © 2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS9535-04
February 2016
RT9535
Operation
The RT9535 is a current mode PWM step-down
switching charger controller. The battery DC charge
current is programmed by a resistor R4 at the ISET pin
and the ratio of sense resistor RS2 over RS1 in the
typical application circuit. Amplifier CA converts the
charge current through RS1 to a much lower sampled
current I
CHG
(I
CHG
= I
BATT
x RS1 / RS2) fed into the
ISET pin. Amplifier EA compares the output of CA with
2.5V reference voltage and drives the PWM loop to
force them to be equal. Note that ICHG has both AC
and DC components. High DC accuracy is achieved
with averaging filter R3 and C3 at ISET pin. I
CHG
is
mirrored to go through R4 and generates a ramp signal
that is fed to the PWM control comparator, forming the
current mode inner loop. An internal LDO generates a
5V to power topside FET gate driver. For batteries like
lithium that require both constant current and constant
voltage charging, the 0.5% 2.5V reference and the
voltage amplifier VA reduce the charge current when
battery voltage reaches the normal charge voltage level.
For NiMH and NiCd, VA can be used for over voltage
protection.
CL Amplifier
The amplifier CL monitors and limits the input current,
normally from the AC adapter, to a preset level (100mV
/ RS4). At input current limit, CL will supply the
programming current at ISET pin, thus reducing battery
charging current.
Charge STATUS
When the charger is in voltage mode and the charge
current level is reduced to 17%, STATUS pin will turn to
logic high. This charge completion signal can be used
to start a timer for charge termination. A 0.1F
capacitor from STATUS to ground is needed to filter the
sampled charging current ripple.
ACDRV Driver
The ACDRV pin drives an external P-MOSFET to avoid
reverse current from battery to input supply. When
input supply is removed, the RT9535 goes into a low
current, 10A maximum, sleep mode as VIN drops
below the battery voltage.
Copyright © 2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS9535-04
February 2016
www.richtek.com
5
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