RT9535
High Efficiency Switching Mode Battery Charger
General Description
Features
The RT9535 is a PWM switch mode battery charger
Fast Charging for Li-Ion, NiMH and NiCd Batteries
controller to fast charge single or multiple Li-Ion, NiMH
Adjustable Battery Voltages from 2.5V to 22V
and NiCd batteries, using constant current or constant
High Efficiency : Up to 95%
voltage control. Maximum current can be easily
Charging Current Programmed by Resistor
programmed by external resistor. The constant voltage
Precision 0.5% Charging Voltage Accuracy
output can support up to 22V with 0.5% accuracy.
Provide 5% Charging Current Accuracy
A third control loop limits the input current drawing from
Input Current Limit Maximizes Charging Rate
the adapter during charging. This allows simultaneous
500kHz Switching Frequency
operation of the equipment and fast battery charging
Flag Indicates Li-Ion Charge Completion
without over loading to the adapter.
Auto Shutdown with Adapter Removal
The RT9535 can charge batteries from 2.5V to 22V
Only 10A Battery Reverse Current when Idle
with dropout voltage as low as 0.4V. A logic output
indicates Li-Ion full charge when current drops to 17%
Applications
Notebook Computers
Portable Instruments
Chargers for Li-lon, NiMH, NiCd and Lead Acid
of the full-scale programmed charge current.
The RT9535 is available in the WQFN-24L 4x4
package.
Rechargeable Batteries
Simplified Application Circuit
RS4
M1
To System Power
VIN
CIN
C1
R2
C2
R1
ACN
RT9535
ACP
ACDRV
HSD
D2
D3
V5V
To VHH Pin
R9
NTC
RNTC
EN
C7
R10
VIN
BOOT
ISET
VC
R3
R4
C3
SS
R5
C5
C4
VFB
VFB
SGND
June 2015
RS1
VBATT
CBATT
RS3
PGND
RS2
RF2
To VFB Pin
SNSH
RF1
SNSL
FBR
BATT
VHH
VHH
STATUS
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
L1
D1
FBR
GND
(Exposed Pad)
DS9535-03
C8
SW
To FBR Pin
C9
is a registered trademark of Richtek Technology Corporation.
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1
RT9535
Ordering Information
Marking Information
RT9535
Package Type
QW : WQFN-24L 4x4 (W-Type)
(Exposed Pad-Option 1)
1J=YM
DNN
1J= : Product Code
YMDNN : Date Code
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
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
GND
V5V
VIN
BOOT
HSD
HSD
(TOP VIEW)
24 23 22 21 20 19
ACN
ACP
ACDRV
EN
SS
ISET
1
18
2
17
3
16
GND
4
15
25
5
6
14
13
8
9 10 11 12
VC
STATUS
NTC
FBR
VFB
VHH
7
SW
SW
PGND
SNSH
SNSL
BATT
WQFN-24L 4x4
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is a registered trademark of Richtek Technology Corporation.
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RT9535
Functional Pin Description
Pin No.
Pin Name
Pin Function
1
ACN
Negative Terminal to Sense Input Current. A filter is needed to filter out the
500kHz switching noise.
2
ACP
Positive Terminal to Sense Input Current.
3
ACDRV
Drive Signal for the Gate of Input Power PFET.
4
EN
Enable Control Input (Active High). It must be connected to a logical voltage or
pulled up to VIN with a 100k resistor.
5
SS
Soft-Start Control Input. SS controls the soft-start time. Connect a capacitor
from SS pin to GND to set the soft-start time.
6
ISET
Charge Current Setting and System Loop Compensation Pin. Connect a
resistor from this pin to ground to set the charge current.
7
VC
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.
8
STATUS
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.
9
NTC
Input for an external NTC thermistor for battery temperature monitoring.
10
FBR
Negative Terminal of External Resistor Divider for Battery Voltage Feedback.
11
VFB
Battery Voltage Feedback. Using an external resistor divider to set battery full
charge voltage.
12
VHH
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.
13
BATT
Battery Voltage Sensing Input. A 10F or larger X5R ceramic capacitor is
recommended for filtering charge current ripple and stability purpose.
14
SNSL
Negative Terminal for Sensing Charge Current.
15
SNSH
Positive Terminal for Sensing Charge Current.
16
PGND
Power Ground.
17, 18
SW
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.
19, 20
HSD
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.
21
BOOT
Bootstrap Supply for the High-Side Power Switch Gate Driver and Control
Circuitry. In normal operation, VBOOT ≈ VSW + 5V.
22
VIN
Input Power Supply. Connect a low ESR capacitor of 10F or higher from this
pin to ground for good bypass.
23
V5V
24
GND
25
(Exposed Pad)
GND
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.
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS9535-03
June 2015
is a registered trademark of Richtek Technology Corporation.
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RT9535
Function Block Diagram
VIN
ACDRV
NTC
ACN
R1
200k
5V
1.4V
C3
EN
THERMISTOR
DRIVER
0.5μA
5V
VREF
2.5V
REFERENCE
SD
VIN
UVLO
V5V
LDO
+
VIN
BATT
C2
0.4V
UVLO
GND
3.9V
IVA
ICHG
VHH
STATUS
SLOP COMP
ICHG
5
OSCILLATOR
BOOT
R2
SNSH
CA
SNSL
ICHG
PWM
C1
IVA
VFB
VREF
2.5V
FBR
EA
VREF
2.5V
HSD
S
R
VA
SD
1.3V
100mV
ACN
Soft-Start
ICL
+
ACP
CL
COUNTER
ISET
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SW
SS
VC
PGND
is a registered trademark of Richtek Technology Corporation.
DS9535-03
June 2015
RT9535
Operation
The RT9535 is a current mode PWM step-down
CL Amplifier
switching charger controller. The battery DC charge
The amplifier CL monitors and limits the input current,
current is programmed by a resistor R4 at the ISET pin
normally from the AC adapter, to a preset level (100mV
and the ratio of sense resistor RS2 over RS1 in the
/ RS4). At input current limit, CL will supply the
typical application circuit. Amplifier CA converts the
programming current at ISET pin, thus reducing battery
charge current through RS1 to a much lower sampled
charging current.
current ICHG (ICHG = IBATT 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
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
with averaging filter R3 and C3 at ISET pin. ICHG is
mirrored to go through R4 and generates a ramp signal
that is fed to the PWM control comparator, forming the
capacitor from STATUS to ground is needed to filter the
sampled charging current ripple.
current mode inner loop. An internal LDO generates a
ACDRV Driver
5V to power topside FET gate driver. For batteries like
The ACDRV pin drives an external P-MOSFET to avoid
lithium that require both constant current and constant
reverse current from battery to input supply. When
voltage charging, the 0.5% 2.5V reference and the
input supply is removed, the RT9535 goes into a low
voltage amplifier VA reduce the charge current when
current, 10A maximum, sleep mode as VIN drops
battery voltage reaches the normal charge voltage level.
below the battery voltage.
For NiMH and NiCd, VA can be used for over voltage
protection.
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS9535-03
June 2015
is a registered trademark of Richtek Technology Corporation.
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RT9535
Absolute Maximum Ratings
(Note 1)
VHH, EN to GND ------------------------------------------------------------------------------- 0.3V to 36V
VIN, SW, HSD, ACN to GND -------------------------------------------------------------- 0.3V to 30V
ACDRV ------------------------------------------------------------------------------------------- (ACN 6V) to (ACN 0.3V)
ACP ------------------------------------------------------------------------------------------------ (ACN 0.3V) to (ACN 0.6V)
BATT to GND------------------------------------------------------------------------------------ 0.3V to 28V
ISET, VC, VFB, V5V to GND ---------------------------------------------------------------- 0.3V to 6V
SNSL ---------------------------------------------------------------------------------------------- (BATT 0.3V) to (BATT 0.3V)
SNSH---------------------------------------------------------------------------------------------- (SNSL 0.3V) to (SNSL 0.3V)
BOOT --------------------------------------------------------------------------------------------- (SW 0.3V) to (SW 6V)
Power Dissipation, PD @ TA = 25C
WQFN-24L 4x4 --------------------------------------------------------------------------------- 3.57W
Package Thermal Resistance
(Note 2)
WQFN-24L 4x4, JA --------------------------------------------------------------------------- 28C/W
WQFN-24L 4x4, JC --------------------------------------------------------------------------- 7C/W
Lead Temperature (Soldering, 10 sec.) --------------------------------------------------- 260C
Junction Temperature ------------------------------------------------------------------------- 150C
Storage Temperature Range ---------------------------------------------------------------- 65C to 150C
ESD Susceptibility
(Note 3)
HBM (Human Body Model) ------------------------------------------------------------------ 2kV
MM (Machine Model) -------------------------------------------------------------------------- 200V
Recommended Operating Conditions
(Note 4)
Supply Input Voltage -------------------------------------------------------------------------- 4.5V to 28V
Battery Voltage, VBAT ------------------------------------------------------------------------ 2.5V to 22V
Ambient Temperature Range---------------------------------------------------------------- 40C to 85C
Junction Temperature Range --------------------------------------------------------------- 40C to 125C
Electrical Characteristics
(VIN = VBAT + 3V, VBAT is the full charge voltage, pull-up EN to VIN with 100k resistor, TA = 25C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
0.5
1.3
2
mA
--
--
12
A
--
--
10
A
VIN Under-Voltage Lockout VUVLO
3.6
3.8
4.3
V
VIN Under-Voltage Lockout VUVLO_
Hysteresis
HYS
--
300
--
mV
Overall
Supply Quiescent Current
IQ
No Charge Current
Supply Shutdown Current
ISD
Reverse Current from
Battery
IREV
VEN = 0
VIN Floating, VEN = 0
VBATT = VSW = VSNSH = VSNSL =
20V
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is a registered trademark of Richtek Technology Corporation.
DS9535-03
June 2015
RT9535
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
2.488
2.5
2.512
V
Reference
Reference Voltage
VFB
FB Bias current
IFB
VFB = 2.5V
--
--
0.1
A
FBR to GND Resistance
RFBR
SD = 2V
55
65
75
SD = 0V
--
--
1
A
R4 = 10k, RS3 = RS2 = 402,
Measure the Voltage Drop Across
RS1
95
100
105
mV
−1
--
--
mA
--
20
25
%
FBR leakage Current
Charge Current
Full-Scale Charge Current
Sense Voltage
VICHG
ISET Output Current
IISET
Termination current Set
Factor
VITM
1/5-Scale Charge Current when
STATUS from Low to High
SNSL Bias Current
ISNSH
No Charge Current
−36
−12
−6
A
SNSH Bias Current
ISNSH
No Charge Current
−36
−12
−6
A
--
--
2
V
Battery Voltage
VHH Minimum Voltage with
VHH
Respect to BATT
VIN Minimum Voltage with
Respect to BATT
VDROP
(Note 5)
--
0.3
0.4
V
VHH Input Current
IVHH
VIN = 28V
40
95
150
A
BATT Bias Current
IBATT
VEN = 0, VBATT = VSW = VSNSH =
VSNSL = 20V
−30
−15
−8
A
VC Pin Current
IVC
VVC = 0V
−25
−15
−1
A
Input Current Limit Sense
Voltage
VILMT
Measure the Voltage Drop Across
RS4
95
100
105
mV
ACN Input Current
IACN
VACP − VACN = 0.1V
8
16
34
A
ACP Input Current
IACP
VACP − VACN = 0.1V
25
50
80
A
ACDRV ON Voltage
VACON
Measure the Voltage (VACN −
VACDRV)
4
5.4
6
V
ACDRV OFF Voltage
VACOFF
Measure the Voltage (VACN −
VACDRV), VEN = 0V
--
--
0.1
V
ARDRV Pull-Down Current IACPD
VACN − VACDRV = 3.8V
5
10
30
A
ARDRV Pull-Up Current
VACN − VACDRV = 0.5V, VEN = 0V
−10
−5
−2
A
fOSC
450
500
550
kHz
RON
--
150
--
m
Input Current Limit
IACPU
Switch Characteristics
Switching Frequency
High-Side Switch
On-Resistance
High-Side Switch leakage
Current
BOOT Leakage Current
IHSD
VHSD = 30V, VEN = 0V
--
--
10
A
IBOOT
VBOOT = 30V, VEN = 0V (Note 5)
--
1
--
A
VVC = 0V
95
--
--
%
VSW = 28V, VEN = 0V
--
--
10
A
Maximum Duty
SW Leakage Current
ILKGL
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS9535-03
June 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
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RT9535
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
50mA Load at V5V, VVC = 0V
4
5
6
V
STATUS Cap = 1F
--
5
--
V
Regulator and Logic Characteristics
LDO Output Voltage
VLDO
STATUS High Voltage
EN Input
Voltage
Logic-High
VENH
2.5
--
--
Logic-Low
VENL
--
--
0.6
--
--
10
A
1.5
3.3
6
A
EN Input Current
IEN
0V ≤ VEN ≤ 5V
Soft-Start Sourcing Current ISS
V
Thermal Comparator and Protection
NTC Threshold, Cold
VCOLD
NTC Threshold, Hot
VHOT
NTC Disable Threshold
VDISNTC
NTC Bias Current
INTC
Thermal Shutdown
Temperature
Thermal Shutdown
Hysteresis
73.5% 75% 76.5%
VV5V
VV5V
VV5V
31% 32.5% 34%
NTC Voltage Rising, 1% Hysteresis
VV5V
VV5V
VV5V
0.2% 1.7% 3.2%
NTC Voltage Rising, 1% Hysteresis
VV5V
VV5V
VV5V
NTC Voltage Rising, 1% Hysteresis
V
V
V
--
2
10
A
TSD
(Note 5)
--
160
--
°C
TSD
(Note 5)
--
30
--
°C
Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are
stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the
operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may affect
device reliability.
Note 2. JA is measured at TA = 25C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. JC is
measured at the exposed pad of the package.
Note 3. Devices are ESD sensitive. Handling precaution recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Note 5. Guaranteed by design, not subjected to production test.
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
DS9535-03
June 2015
RT9535
Typical Application Circuit
M1
SI 4435
RS4
50m
VIN
CIN
10μF
C1
33nF
R1
100k
To System Power
C2
10μF x 2
R2
56
1
2
3
4
ACN
HSD
RT9535
V5V
ACP
ACDRV
19,20
D2
23
To VHH Pin
R9
100k
NTC 9
RNTC
EN
D3
C7
1μF
R10
100k
22 VIN
R3
(Optional)
C3
(Optional)
R4
10k
C10
(Optional)
R5
1k
C5
VFB
0.01μF
C4
3.3nF
FBR
VHH
C8
0.1μF
17, 18
SW
5
SS
11 VFB
24
21
BOOT
6
ISET
7
VC
L1
10μH
RS1
0.1
VBATT
D1
PGND
SNSH
SGND
RS3
402
16
TVS
To VFB Pin
15
RF1
100k
SNSL 14
13
BATT
8
STATUS
10 FBR
12
VHH
CBATT
10μF
RF2
390k
RS2
402
To FBR Pin
C9
0.1μF
GND
(Exposed Pad)
25
Note : For application with removable battery, a TVS with appropriate rating is required as shown above.
Figure 1. System Power from VIN (VIN = 15V to 28V, 3 – cell, Icharge = 1A)
D4
PMEG4030
VIN
CIN
10μF
C2
10μF x 2
R1
1 ACN
100k
2
3
4
RT9535
HSD
V5V
ACP
ACDRV
19,20
D2
23
To VHH Pin
NTC 9
RNTC
EN
D3
R9
100k
R10
100k
C7
1μF
22 VIN
R3
(Optional)
C3
(Optional)
R4
10k
R5
1k
C4
3.3nF
C10
(Optional)
C5
VFB
0.01μF
FBR
VHH
BOOT
6
ISET
7
VC
5
SW
11 VFB
PGND
24
SNSH
10
12
FBR
VHH
C8
0.1μF
17, 18
L1
10μH
RS3
402
16
RS2
402
RF2
390k
CBATT
10μF
RS4
50m
C1
33nF
To VFB Pin
15
RF1
100k
SNSL 14
13
BATT
8
STATUS
GND
(Exposed Pad)
25
M1
SI 4435
RS1
0.1
D1
SS
SGND
21
VBATT
ACP
To FBR Pin
To System Power
R2
56
ACN
BATT
TVS
ACDRV
C9
0.1μF
Note : For application with removable battery, a TVS with appropriate rating is required as shown above.
Figure 2. System Power from VBATT (VIN = 15V to 28V, 3 – cell, if Isystem = 0.5A than Icharge = 1A)
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS9535-03
June 2015
is a registered trademark of Richtek Technology Corporation.
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RT9535
Typical Operating Characteristics
Efficiency vs. Charge Current
100
95
95
Efficiency (%)
Efficiency (%)
Efficiency vs. Supply Voltage
100
90
85
1 Cell : VBATT
2 Cell : VBATT
3 Cell : VBATT
4 Cell : VBATT
5 Cell : VBATT
80
75
= 4V
= 8V
= 12V
= 16V
= 20V
90
85
1 Cell : VIN = 12V, VBATT
2 Cell : VIN = 24V, VBATT
3 Cell : VIN = 24V, VBATT
4 Cell : VIN = 24V, VBATT
5 Cell : VIN = 24V, VBATT
80
75
IBATT = 1A
70
70
0
5
10
15
20
25
0.5
30
1
1.5
2
2.5
Charge Current (A)
Supply Voltage (V)
Charge Current vs. Supply Voltage
Supply Current vs. Temperature
1.20
1.2
1.12
1.08
1.04
= 4V
= 8V
= 12V
= 16V
= 20V
1.0
Supply Current (mA)
1 Cell : VIN = 12V, VBATT
2 Cell : VIN = 24V, VBATT
3 Cell : VIN = 24V, VBATT
4 Cell : VIN = 24V, VBATT
5 Cell : VIN = 24V, VBATT
1.16
Charge Current (A)
= 4V
= 8V
= 12V
= 16V
= 20V
1.00
0.96
0.92
0.88
0.8
0.6
0.4
VIN = 28V
VIN = 12V
0.2
0.84
0.80
0.0
0
10
20
30
-50
-25
Supply Voltage (V)
0
25
50
75
100
125
Temperature (℃)
Shutdown Current vs. Temperature
V5V Voltage vs. Temperature
45
5.00
4.95
35
V5V Voltage (V)
Shutdown Current (A)
40
30
25
20
VIN = 28V
VIN = 12V
15
10
4.90
4.85
4.80
4.75
5
VIN = 12V, IV5V = 40mA
0
4.70
-50
-25
0
25
50
75
100
Temperature (℃)
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10
125
-50
-25
0
25
50
75
100
125
Temperature (℃)
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DS9535-03
June 2015
RT9535
VICHG vs. Temperature
VFB Voltage vs. Temperature
110
2.55
108
106
2.53
VFB Voltage (V)
VICHG (mV)
104
102
100
98
96
94
92
90
-50
-25
0
25
50
2.51
2.49
VIN = 4.5V
VIN = 12V
VIN = 28V
2.47
100
2.45
75
125
VIN = 4.5V
VIN = 12V
VIN = 28V
-50
Temperature (°C)
25
50
75
100
125
BATT Bias Current vs.Temperature
Switching Frequency vs. Supply Voltage
14
12
505
BATT Bias Current (A)
Switching Frequency (kHz)
0
Temperature (°C)
510
500
495
490
485
10
8
6
4
2
0
480
0
5
10
15
20
25
30
-50
-25
0
25
50
75
100
125
Temperature (℃)
Supply Voltage (V)
Charge Enable and Disable
Adapter Insert and Remove
VBATT
(2V/Div)
SW-GND
(10V/Div)
VBATT
(2V/Div)
SW-GND
(10V/Div)
EN
(2V/Div)
VIN
(5V/Div)
IBATT
(500mA/Div)
VIN = 12V, VBATT = 4V, IBATT = 1A
Time (25ms/Div)
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-25
June 2015
IBATT
(500mA/Div)
VIN = 12V, VBATT = 4V, IBATT = 1A
Time (25ms/Div)
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RT9535
Charge Enable
Charge Disable
VBATT
(2V/Div)
VBATT
(2V/Div)
SW-GND
(10V/Div)
SW-GND
(10V/Div)
EN
(2V/Div)
EN
(2V/Div)
IBATT
(500mA/Div)
VIN = 12V, VBATT = 4V, IBATT = 1A
IBATT
(500mA/Div)
Time (10ms/Div)
Time (10ms/Div)
Switching
VBATT
(5V/Div)
VBATT
(5V/Div)
IL
(500mA/Div)
VIN = 12V, VBATT = 4V, IBATT = 1A
Time (1s/Div)
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12
BATT to GND Short Response
IIN
(1A/Div)
IBATT
(1A/Div)
IL
(500mA/Div)
SW-GND
(10V/Div)
VIN = 12V, VBATT = 4V, IBATT = 1A
SW-GND
(10V/Div)
VIN = 12V, VBATT = 4V, IBATT = 1A
Time (10ms/Div)
is a registered trademark of Richtek Technology Corporation.
DS9535-03
June 2015
RT9535
Application Information
Input and Output Capacitors
and the battery impedance is raised to 4 with a bead
In the typical application circuit, the input capacitor (C2)
or inductor, only 5% of the ripple current will flow in the
is assumed to absorb all input switching ripple current
battery.
in the converter, so it must have adequate ripple
current rating. Typically, at high charging currents, the
converter will operate in continuous conduction mode.
In this case, the RMS current IRMSIN of the input
capacitor C2 can be estimated by the equation :
IRMSIN = IBATT D D2
Inductor
The inductor value will be changed for more or less
current ripple. The higher the inductance, the lower the
current ripple will be. As the physical size is kept the
same, typically, higher inductance will result in higher
series resistance and lower saturation current. A good
tradeoff is to choose the inductor so that the current
Where IBATT is the battery charge current and D is the
duty cycle. In worst case, the RMS ripple current will be
equal to one half of output charging current at 50% duty
cycle. For example, IBATT = 2A, the maximum RMS
current will be 1A. A low-ESR ceramic capacitor such
as X7R or X5R is preferred for the input-decoupling
capacitor and should be placed to the drain of the
high-side MOSFET and source of the low-side
MOSFET as close as possible. The voltage rating of
the capacitor must be higher than the normal input
voltage level. Above 20F capacitance is suggested for
ripple is approximately 30% to 50% of the full-scale
charge current. The inductor value is calculated as :
L1 =
VBATT VVIN VBATT
VVIN fOSC ΔIL
Where IL is the inductor current ripple. For example,
VVIN = 19V, choose the inductor current ripple to be
40% of the full-scale charge current in the typical
application circuit for 2A, 2-cell battery charger, IL =
0.8A, VBATT = 8.4V, calculate L1 to be 12H. So
choose L1 to be 10H which is close to 12H.
typical of 2A charging current.
Soft-Start and Under-Voltage Lockout
The output capacitor (CBATT) is also assumed to
The soft-start is controlled by the voltage rise time at
absorb output switching current ripple. The general
VC pin. There are internal soft-start and external
formula for capacitor current is :
soft-start in the RT9535. With a 1F capacitor, time to
IRMSCB
VBATT
VBATT 1
VVIN
=
2 3 L1 fosc
reach full charge current is about 60ms and it is
assumed that input voltage to the charger will reach full
value in less than 60ms. The capacitor can be
For example, VVIN = 19V, VBATT = 8.4V, L1 = 10H,
increased if longer input start-up times are needed.
and f OSC = 475kHz, IRMS = 0.15A.
For the RT9535, it provides Under-Voltage Lockout
EMI considerations usually make it desirable to
(UVLO) protection. If LDO output voltage is lower than
minimize ripple current in the battery leads. Beads or
3.9V, the internal top side power FET and input power
inductors may be added to increase battery impedance
FET M1 will be cut off. This will protect the adapter from
at the 475kHz switching frequency. Switching ripple
entering a quasi “latch” state where the adapter output
current splits between the battery and the output
stays in a current limited state at reduced output
capacitor depending on the ESR of the output capacitor
voltage.
and the battery impedance. If the ESR of COUT is 0.2
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS9535-03
June 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
13
RT9535
Adapter Current Limiting
For for 40°C to 85°C temperature range, the minimum
An important feature of RT9535 is the ability to
value for R4 is 6k.
automatically adjust charge current to a level which
The maximum value of R4 should be lower than 60k.
avoids overloading the wall adapter. This allows the
It is critical to have a good Kelvin connection on the
product to operate, and at the same time batteries are
current sense resistor RS1 to minimize stray resistive
being charged without complex load management
and inductive pickup. RS1 should have low parasitic
algorithms. Additionally, batteries will automatically be
inductance (typical 3nH or less). The layout path from
charged at the maximum possible rate of which the
RS2 and RS3 to RS1 should be kept away from the fast
adapter is capable. This is accomplished by sensing
switching SW node. A 1nF ceramic capacitor can be
total adapter output current and adjusting charge
used across SNSH and SNSL and be kept away from
current downward if a preset adapter current limit is
the fast switching SW node.
exceeded. Amplifier CL in typical application circuit
senses the voltage across RS4, connected between
the ACP and ACN pins. When this voltage exceeds
100mV, the amplifier will override programmed charge
current to limit adapter current to 100mV/RS4. A low
pass filter formed by 56 and 33nF is required to
eliminate switching noise.
Battery Voltage Regulation
The RT9535 uses high-accuracy voltage bandgap and
regulator for the high charging-voltage accuracy. The
charge voltage is programmed via a resistor divider
from the battery to ground, with the midpoint tied to the
VFB pin. The voltage at the VFB pin is regulated to
2.5V, giving the following equation for the regulation
Full-Scale Charge Current Programming
voltage :
The basic formula for full-scale charge current is (see
RF2
VBATT = 2.5 1 +
RF1
Block Diagram) :
VREF RS2
IBATT =
R4 RS1
where RF2 is connected from VFB to the battery and
RF1 is connected from VFB to GND.
Where R4 is the total resistance from ISET pin to
ground. For the sense amplifier CA biasing purpose,
Charging
RS3 should have the same value as RS2 with 1%
The 2A Battery Charger (typical application circuit)
accuracy. For example, 2A full-scale charging current is
charges lithium-ion batteries at a constant 2A until
needed. For low power dissipation on RS1 and enough
battery voltage reaches the setting value. The charger
signal to drive the amplifier CA, let RS1 = 100mV / 2A =
will then automatically go into a constant voltage mode
50m. This limits RS1 power to 0.2W. Let R4 = 10k,
with current decreasing to near zero over time as the
then :
battery reaches full charge.
RS2 = RS3 =
IBATT R4 RS1 2A 10k 0.05
=
= 400Ω
VREF
2.5V
Charging Completion
Some battery manufacturers recommend termination of
Note that for charge current accuracy and noise
immunity, 100mV full scale level across the sense
resistor RS1 is required. Consequently, both RS2 and
RS3 should be 399. For for 0°C to 85°C temperature
constant voltage float mode after charge current has
dropped below a specified level (typically around 20%
of the full-scale charge current) and a further time-out
period of 30 minutes to 90 minutes has elapsed. Check
range, the minimum value for R4 is 5.5k.
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14
is a registered trademark of Richtek Technology Corporation.
DS9535-03
June 2015
RT9535
with manufacturers for details. The RT9535 provides a
VACN. In sleep mode, when VIN is removed, ACDRV
signal at the STATUS pin when charging is in voltage
will clamp M1 VSG to less than 0.1V.
mode and charge current is reduced to 17% of
full-scale charge current, assuming full-scale charge
current is programmed to have 100mV across the
current sense resistor (VRS1).
The charge current sample ICHG is compared with the
output current IVA of voltage amplifier VA. When the
charge current drops to 17% of full-scale charge
current, ICHG will be equal to 20% of IVA and the
STATUS pin voltage will go logic high and can be used
to start an external timer. When this feature is used, a
capacitor of at least 0.1F is required at the STATUS
pin to filter out the switching noise. If this feature is not
used, the capacitor is not needed.
Dropout Operation
The RT9535 can charge the battery even when VIN
goes as low as 2V above the combined voltages of the
battery and the drops on the sense resistor as well as
parasitic wiring. This low VIN sometimes forces 100%
duty cycle and TG stays on for many switching cycles.
While TG stays on, the voltage VBOOT across the
capacitor C8 drops down slowly because the current
sink at BOOT pin. C8 needs to be recharged before
VBOOT drops too low to keep the topside switch on.
A unique design allows the RT9535 to operate under
these conditions. If SW pin voltage keeps larger than
1.3V for 32 oscillation periods, topside power FET will
be turned off and an internal FET will be turned on to
Shutdown
When adapter power is removed, VIN will drift down.
As soon as VIN goes down to 0.1V above VBATT, the
RT9535 will go into sleep mode drawing only ~10μA
from the battery. There are two ways to stop switching:
pulling the EN pin low or pulling the VC pin low. Pulling
the EN pin low will shut down the whole chip. Pulling
the VC pin low will only stop switching and LDO stays
work. Make sure there is a pull-up resistor on the EN
pin even if the EN pin is not used, otherwise internal
pull-down current will keep the EN pin low to shut down
mode when power turns on.
Charger Protection
If the VIN connector of typical application circuit can be
instantaneously shorted to ground, the P-MOSFET M1
must be quickly turned off, otherwise, high reverse
surge current might damage M1. An internal transient
enhancement circuit is designed to quickly charge
ACDRV pin voltage to ACN pin voltage.
Note that the RT9535 will operate even when VBATT is
grounded. If VBATT of typical application circuit charger
gets shorted to ground very quickly from a high battery
voltage, slow loop response may allow charge current
to build up and damage the topside N-MOSFET M2. A
small diode from the EN pin to VBATT will shut down
switching and protect the charger.
pull SW pin down. This function refreshes VBOOT
Temperature Qualification
voltage to a higher value. It is important to use 0.1F to
The controller RT9535 continuously monitors battery
hold VBOOT up for a sufficient amount of time. The
temperature by measuring the voltage between the
P-MOSFET M1 is optional and can be replaced with a
NTC pin and GND. A negative temperature coefficient
diode if VIN is at least 2.5V higher than VBATT. The
thermistor (NTC) and an external voltage divider
gate control pin ACDRV turns on M1 when V5V gets up
typically develop this voltage. The controller compares
above the under-voltage lockout level and is clamped
this voltage against its internal thresholds to determine
internally to 5V below VACN. In sleep mode, when VIN
if charging is allowed. To initiate a charge cycle, the
is removed, ACDRV will clamped internally to 5V below
battery temperature must be within the VCOLD. If
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS9535-03
June 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
15
RT9535
battery temperature is outside of this range, the
Thermal Considerations
controller suspends charge and the safety timer and
For continuous operation, do not exceed absolute
waits until the battery temperature is within the VCOLD
maximum junction temperature. The maximum power
to VHOT range. During the charge cycle, the battery
dissipation depends on the thermal resistance of the IC
temperature must be within the VCOLD and VDISNTC
package, PCB layout, rate of surrounding airflow, and
thresholds. If the battery temperature is outside of this
difference between junction and ambient temperature.
range, the controller suspends charge and waits until
The maximum power dissipation can be calculated by
the battery temperature is within the VCOLD to VHOT
the following formula :
range. The controller suspends charge by turning off
PD(MAX) = (TJ(MAX) TA) / JA
the PWM charge FETs.
where TJ(MAX) is the maximum junction temperature,
TA is the ambient temperature, and JA is the junction to
ambient thermal resistance.
For recommended operating condition specifications,
the maximum junction temperature is 125C. The
junction to ambient thermal resistance, JA, is layout
dependent. For WQFN-24L 4x4 package, the thermal
resistance, JA, is 28C/W on a standard JEDEC 51-7
four-layer thermal test board. The maximum power
Assuming a 103AT NTC thermistor on the battery pack
as shown in the below, the values of RT1 and RT2 can
be determined by using the following equations:
dissipation at TA = 25C can be calculated by the
following formula :
PD(MAX) = (125C 25C) / (28C/W) = 3.57W for
WQFN-24L 4x4 package
1
1
VV5V RTHCOLD RTHHOT
V
V
HOT
COLD
RT2 =
VV5V
VV5V
RTHHOT
1 RTHCOLD
1
V
V
HOT
COLD
The maximum power dissipation depends on the
operating ambient temperature for fixed TJ(MAX) and
thermal resistance, JA. The derating curve in Figure 3
allows the designer to see the effect of rising ambient
VV5V
1
VCOLD
RT1 =
1
1
RT2 RTHCOLD
temperature on the maximum power dissipation.
V5V
RT9535
RT1
NTC
RT2
RTH
103AT
TS Resistor Network
Where RTHCOLD and RTHHOT which have defined in the
spec of the 103AT NTC thermistor.
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is a registered trademark of Richtek Technology Corporation.
DS9535-03
June 2015
RT9535
Maximum Power Dissipation (W)1
Layout Consideration
Switch rise and fall times are under 20ns for maximum
5.0
efficiency. To prevent radiation, the SW pin, the rectifier
Four-Layer PCB
4.0
Schottky diode D1 and input bypass capacitor leads
should be kept as short as possible. A ground plane
3.0
should be used under the switching circuitry to prevent
inter-plane coupling and to act as a thermal spreading
2.0
path. Note that the rectifier Schottky diode D1 is
1.0
probably the most heat dissipating device in the
charging system. The voltage drop on a 2A Schottky
0.0
0
25
50
75
100
125
diode can be 0.5V. With 50% duty cycle, the power
Ambient Temperature (°C)
dissipation can go as high as 0.5W. Expanded traces
Figure 3. Derating Curve of Maximum Power
should be used for the diode leads for low thermal
Dissipation
resistance. Another large heat dissipating device is
probably the inductor. The fast switching high current
ground path including the MOSFETs, D1 and input
bypass capacitor C2 should be kept very short. Another
smaller input bypass (1F ceramic or larger paralleled
with CIN) should be placed to VIN pin and GND pin as
close as possible.
SI
Input Power, VIN
18
ACP 2
17 SW
5
ISET
6
Locate the Compensation components to
the SS/VC/ISET pin as close as possible.
C4
R5
C9
GND
17
RSH
15 SNSH
RS1
14 SNSL
RS3
BATT
SS
16 PGND
RSH
RSL
13 BATT
7
8
9 10 11 12
VFB
4
VBATT
VHH
R1 EN
FBR
3
NTC
ACDRV
CBATT
RS2
L1
ACN 1
VBATTH
VIN
HSD
D1
24 23 22 21 20 19
VC
C3
VIN
C5
R3
R4
Place these Power Components as
close to the SW pin as possible.
C2
BOOT
GND
D3
VHH
C1
CIN
STATUS
GND
RS4
ACN
C7
C8
D2
V5V
SW
RB
BOOT
ACP
ACDRV
RSL
Input capacitor and C7 must be
placed as close to the IC as
possible.
C6
R6
NTC
VBATTH
R7
RF2
GND
RF1
V5V
FBR
C6 must be placed as close
to the IC as possible.
Figure 4. PCB Layout Guide
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS9535-03
June 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
17
RT9535
Outline Dimension
Symbol
D2
E2
Dimensions In Millimeters
Dimensions In Inches
Min
Max
Min
Max
A
0.700
0.800
0.028
0.031
A1
0.000
0.050
0.000
0.002
A3
0.175
0.250
0.007
0.010
b
0.180
0.300
0.007
0.012
D
3.950
4.050
0.156
0.159
Option 1
2.400
2.500
0.094
0.098
Option 2
2.650
2.750
0.104
0.108
E
3.950
4.050
0.156
0.159
Option 1
2.400
2.500
0.094
0.098
Option 2
2.650
2.750
0.104
0.108
e
L
0.500
0.350
0.020
0.450
0.014
0.018
W-Type 24L QFN 4x4 Package
Richtek Technology Corporation
14F, No. 8, Tai Yuen 1st Street, Chupei City
Hsinchu, Taiwan, R.O.C.
Tel: (8863)5526789
Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should
obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot assume
responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be accurate and
reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may
result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries.
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is a registered trademark of Richtek Technology Corporation.
DS9535-03
June 2015
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