SC820EVB [SEMTECH]
Adapter/USB Dual Input Single-cell Li-ion Charger; 适配器/ USB双输入单节锂离子电池充电器
| 型号： | SC820EVB |
| 厂家： | 
SEMTECH CORPORATION |
| 描述： | Adapter/USB Dual Input Single-cell Li-ion Charger |
| 文件： | 总22页 (文件大小：362K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
SC820
Adapter/USB Dual Input
Single-cell Li-ion Charger
POWER MANAGEMENT
Features
Description
Input voltage protection — 30V
The SC820 is a dual input (adapter/USB) linear single-cell
Li-ion battery charger in an 8 lead 2×2mm MLPD ultra-thin
package. Both inputs will survive sustained input voltage
up to 30V to protect against hot plug overshoot and faulty
charging adapters.
Adapter input automatically selected over USB
Constant voltage — 4.2V, 1% regulation
Charging by current and voltage regulation (CC/CV)
Thermal limiting of charge current
Programmable battery-dependent currents (adapter-
sourced fast-charge & pre-charge, termination)
Programmable source-limited currents (USB-sourced
fast-charge & pre-charge)
Current-limited adapter support — reduces power dis-
sipation in charger IC
USB input limits charge current — prevents Vbus
overload
Instantaneous CC-to-CV transition for faster charging
Three termination options — float-charge, automatic
re-charge, or forced re-charge to keep the battery
topped-off after termination without float-charging
Soft-start — reduces load transients
High operating voltage range — permits use of
unregulated adapters
Complies with CCSA YD/T 1591-2006
Charging begins automatically when a valid input source
is applied to either input. The adapter input is selected
when both input sources are present.
Thermal limiting protects the SC820 from excessive power
dissipation when charging from either source. The SC820
can be programmed to turn off when charging is complete
or to continue operating as an LDO regulator while float-
charging the battery.
The adapter input charges with an adapter operating in
voltage regulation or in current limit to obtain the lowest
possible power dissipation by pulling the VAD input
voltage down to the battery voltage. The VUSB input
dynamically limits load current to automatically prevent
over-loading the USB Vbus supply.
Space saving 2×2×0.6 (mm) MLPD package
Pb free, Halogen free, and RoHS/WEEE compliant
Charge current programming requires two resistors. One
determines battery-capacity dependent currents: adapter
input fast-charge current, pre-charge current, and charge
termination current. The other independently determines
input-limited USB charging currents: USB input fast-
charge and pre-charge current.
Applications
Mobile phones
MP3 players
GPS handheld receivers
Typical Application Circuit
SC820
Battery
Pack
Device
Load
VADAPTER
VAD
ENB
BAT
USB Vbus
VUSB
STATB
GND
2.2 μF
IPRGM
IPUSB
2.2 μF
2.2 μF
© 2009 Semtech Corporation
September 17, 2009
1
SC820
Pin Configuration
Ordering Information
Device
Package
SC820ULTRT(1)(2)
MLPD-UT-8 2×2
Evaluation Board
SC820EVB
Notes:
VAD
VUSB
STATB
GND
ENB
1
2
3
4
8
7
6
5
TOP VIEW
(1) Available in tape and reel only. A reel contains 3,000 devices.
(2) Pb free, halogen free, and RoHS/WEEE compliant.
BAT
IPRGM
IPUSB
T
MLPD-UT8; 2×2, 8 LEAD
θJA = 68°C/W
Marking Information
820
yw
yw = Date Code
2
SC820
Absolute Maximum Ratings
Recommended Operating Conditions
VAD and VUSB (V). . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to +30.0
BAT, IPRGM, IPUSB (V) . . . . . . . . . . . . . . . . . . . . . . -0.3 to +6.5
STATB, ENB (V) . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to VBAT +0.3
VAD Input Current (A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5
VUSB Input Current (A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5
BAT, IPRGM, IPUSB Short-to-GND Duration . . . . . Continuous
ESD Protection Level(1) (kV) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Operating Ambient Temperature (°C) . . . . . . . . . -40 to +85
VAD Operating Voltage(2) (V). . . . . . . . . . . . . . . . 4.60 to 8.20
VUSB Operating Voltage(2) (V). . . . . . . . . . . . . . . 4.70 to 8.20
Thermal Information
Thermal Resistance, Junction to Ambient(3) (°C/W). . . . . 68
Maximum Junction Temperature (°C) . . . . . . . . . . . . . . +150
Storage Temperature Range (°C). . . . . . . . . . . . -65 to +150
Peak IR Reflow Temperature (10s to 30s) (°C) . . . . . . . +260
Exceeding the above specifications may result in permanent damage to the device or device malfunction. Operation outside of the parameters
specified in the Electrical Characteristics section is not recommended.
NOTES:
(1) Tested according to JEDEC standard JESD22-A114D.
(2) Operating Voltage is the input voltage at which the charger is guaranteed to begin operation. These ranges, VTADsel-R Max to VOVP-F Min for the
VAD input, VUVLR Max to VOVP-F Min for the VUSB input, apply to charging sources operating in voltage regulation. Charging sources operating
in current limit may be pulled below these ranges by the charging load. Maximum operating voltage is the maximum Vsupply as defined in
EIA/JEDEC Standard No. 78, paragraph 2.11.
(3) Calculated from package in still air, mounted to 3 x 4.5 (in), 4 layer FR4 PCB with thermal vias under the exposed pad per JESD51 standards.
Electrical Characteristics
Test Conditions: VVAD = VVUSB = 4.75V to 5.25V; CVAD = CVUSB = CBAT = 2.2μF; VBAT = 3.7V; Typ values at 25°C; Min and Max at -40°C < TA < 85°C, unless
specified.
Parameter
Symbol
VTADsel-R
VTADsel-F
VTUSBsel-R
VTUSBsel-F
VTUSBsel-H
VTOVP-R
Conditions
Min
4.30
2.70
Typ
4.45
2.85
4.20
4.00
Max
4.60
3.00
4.35
Units
VAD Select Rising Threshold
VAD Deselect Falling Threshold(1)
VUSB Select Rising Threshold
VUSB Deselect Falling Threshold
VUSB Select Hysteresis
OVP Rising Threshold
V
V
VVAD > VBAT
VVUSB > VBAT
V
VVUSB > VBAT
3.65
100
V
VTUSBsel-R - VTUSBsel-F
VAD or VUSB input
VAD or VUSB input
mV
V
9.6
OVP Falling Threshold
OVP Hysteresis
VTOVP-F
8.2
50
V
VTOVP-H
(VTOVP-R - VTOVP-F
)
mV
VAD Charging Disabled Quiescent
Current
IqVAD_DIS
IqVAD_EN
IqVUSB_DIS
VVUSB = 0V, VENB = VBAT
2
2
2
3
3
3
mA
mA
mA
VAD Charging Enabled Quiescent
Current
VVUSB = 0V, VENB = 0V,
excluding IBAT, IIPRGM, and IIPUSB
VUSB Charging Disabled Quiescent
Current
VVAD = 0V; VENB = VBAT
3
SC820
Electrical Characteristics (continued)
Parameter
Symbol
Conditions
Min
Typ
Max
Units
VUSB Charging Enabled Quiescent
Current
VVAD = 0V, VENB = 0V,
excluding IBAT, IIPRGM, and IIPUSB
IqVUSB_EN
2
3
mA
VUSB Deselected Quiescent Current(2)
IqVUSB_DES
VCV
VVAD ≥ VVUSB
25
50
μA
V
CV Regulation Voltage
IBAT = 50mA, -40°C ≤ TJ ≤ 125°C
4.16
-20
4.20
4.24
Relative to VCV @ 50mA,
VAD = 5V, or VVUSB = 5V and VVAD = 0V,
CV Voltage Load Regulation(3)
VCV_LOAD
10
mV
V
1mA ≤ IBAT ≤ 700mA, -40°C ≤ TJ ≤ 125°C
Re-charge Threshold
VTReQ
VTPreQ
lBAT_V0
lBAT_DIS
VCV — VBAT
60
100
2.90
0.1
140
2.95
1
mV
V
Pre-charge Threshold (rising)
2.85
VBAT = VCV, VVAD = VVUSB = 0V
μA
μA
VBAT = VCV, VVAD = VVUSB = 5V, VENB = 2V
0.1
1
Battery Leakage Current
VBAT = VCV, VVAD = VVUSB = 5V,
ENB not connected
lBAT_MON
0.1
1
μA
IPRGM Programming Resistor
Fast-Charge Current, VAD input
Pre-Charge Current, VAD input
Termination Current, either input
VAD to BAT Dropout Voltage
IPUSB Programming Resistor
Fast-Charge Current, VUSB input
Pre-Charge Current, VUSB input
VUSB to BAT Dropout Voltage
RIPRGM
IFQ_AD
IPreQ_AD
ITERM
VDO_AD
RIPUSB
2.05
643
105
59
29.4
745
173
80
kΩ
mA
mA
mA
V
RIPRGM = 2.94kꢀ, VTPreQ < VBAT < VCV
RIPRGM = 2.94kꢀ, 1.8V < VBAT < VTPreQ
RIPRGM = 2.94kꢀ, VBAT = VCV
694
139
69
IBAT = 700mA, 0°C ≤ TJ ≤ 125°C
0.75
1.0
4.42
427
69
29.4
497
116
1
kΩ
mA
mA
V
IFQ_USB
IPreQ_USB
VDO_USB
RIPUSB = 4.42kꢀ, VTPreQ < VBAT < VCV
RIPUSB = 4.42kꢀ, 1.8V < VBAT < VTPreQ
IBAT = 500mA, 0°C ≤ TJ ≤ 125°C
462
92
0.55
VVAD = 5.0V, VVUSB = 0V,
VTPreQ < VBAT < VCV
IPRGM Fast-charge Regulated Voltage
VIPRGM_FQ
2.04
V
IPRGM Pre-charge Regulated Voltage
IPRGM Termination Threshold Voltage
IPUSB Fast-charge Regulated Voltage
IPUSB Pre-charge Regulated Voltage
VIPRGM_PQ
VTIPRGM_TERM
VIPUSB_FQ
VBAT < VTPreQ
0.408
0.204
2.04
V
V
V
V
VBAT = VCV (either input selected)
VVAD = 0V, VTPreQ < VBAT < VCV
VVAD = 0V, VBAT < VTPreQ
VIPUSB_PQ
0.408
5mA ≤ VUSB supply current limit ≤
500mA, VVAD = 0V,
VUSB Under-Voltage Load Regulation
Limiting Voltage
VUVLR
4.40
4.57
4.70
V
R
IPUSB = 3.65kꢀ (559mA)
4
SC820
Electrical Characteristics (continued)
Parameter
Symbol
Conditions
Min
Typ
130
-50
Max
Units
Thermal Limiting Threshold Tempera-
ture
TTL
°C
Thermal Limiting Rate
ENB Input High Voltage
ENB Input Mid Voltage
ENB Input Low Voltage
iT
TJ > TTL
mA/ °C
VIH
VIM
VIL
1.6
0.7
V
V
V
1.3
0.3
ENB Input High-range Threshold
Input Current
ENB current required to pull ENB from
floating midrange into high range
IIH_TH
IIH_SUS
IIM
23
50
1
μA
μA
μA
Current required to hold ENB in
ENB Input High-range Sustain Input
Current
high range, Min VIH ≤ VENB ≤ VBAT
,
0.3
Min VIH ≤ VBAT ≤ 4.2V
Input will float to mid range when this
load limit is observed.
ENB Input Mid-range Load Limit
-5
5
ENB Input Low-range Input Current
ENB Input Leakage
IIL
0V ≤ VENB ≤ Max VIL
VVIN = 0V, VENB = VBAT = 4.2V
ISTAT_SINK = 2mA
-25
-12
μA
μA
V
IILEAK
1
0.5
1
STATB Output Low Voltage
STATB Output High Current
Notes:
VSTAT_LO
ISTAT_HI
VSTAT = 5V
μA
(1) Sustained operation to VTADsel-F ≤ VVAD is guaranteed only if a current limited charging source applied to VAD is pulled below VTADsel-R by the
charging load; forced VAD voltage below VTADsel-R may in some cases result in regulation errors or other unexpected behavior.
(2) If VAD is the selected input but VVAD < VVUSB, such as when VAD is operating with an adapter in current limit while a VUSB charging source is
applied, IqVUSB_DES will increase to approximately IqVUSB_EN
.
(3) At load currents exceeding 700mA, or at 700mA while at elevated ambient temperature, the charger may enter dropout with a 5V input before
the battery voltage has risen to VCV. See the specification of VDO_AD. Although this is a safe and acceptable mode of operation, specification of
VCV when in dropout is not applicable; higher input voltage will restore the charger to CV regulation in these cases. Note that VBAT is always
less than VCV while in dropout. As the battery state-of-charge increases, the charging current will decrease allowing the battery voltage to rise
to VCV, and CV regulation will begin. This appears as a softening or rounding of the CC-to-CV regulation mode transition, similar to that seen
in chargers with a linear CC-to-CV regulation crossover.
5
SC820
Typical Characteristics
CV Line Regulation
CV Load Regulation
TA = 25οC, VVAD = 5V
TA = 25οC, IBAT = 50mA
4.204
4.2
4.204
4.2
4.196
4.192
4.188
4.184
4.18
4.196
4.192
4.188
4.184
4.18
0
100
200
300
400
500
600
700
800
5
5.5
6
6.5
7
7.5
8
IBAT (mA)
VVAD (V)
CV Temperature Regulation
VVAD = 5V, IBAT = 50mA
CC FQ Line Regulation (AD or USB)
TA = 25οC, VBAT = 3.7V
4.204
4.2
720
680
640
600
560
520
480
440
Ω
RIPRGM or RIPUSB = 2.94k
4.196
4.192
4.188
4.184
4.18
Ω
RIPRGM or RIPUSB = 4.42k
-40
-20
0
20
40
60
80
100
120
4.5
5
5.5
6
6.5
VVAD (V)
7
7.5
8
Ambient Temperature (oC)
CC FQ VBAT Regulation (AD or USB)
CC FQ Temperature Regulation (AD or USB)
VVAD = 5V, VBAT = 3.7V
TA = 25οC, VVAD = 5V
720
680
640
600
560
520
480
440
720
680
640
600
560
520
480
440
Ω
RIPRGM or RIPUSB = 2.94k
Ω
RIPRGM or RIPUSB = 4.42k
2.9
3.1
3.3
3.5
3.7
3.9
4.1
-40
-20
0
20
40
60
80
100
120
Ambient Temperature (oC)
VBAT (V)
6
SC820
Typical Characteristics (continued)
CC PQ Line Regulation (AD or USB)
CC PQ Temperature Regulation (AD or USB)
VVAD = 5V, VBAT = 2.6V
TA = 25οC, VBAT = 2.6V
160
160
150
140
130
120
110
100
90
150
Ω
RIPRGM or RIPUSB = 2.94k
Ω
RIPRGM or RIPUSB = 2.94k
140
130
120
110
100
90
Ω
RIPRGM or RIPUSB = 4.42k
Ω
RIPRGM or RIPUSB = 4.42k
-40
-20
0
20
40
60
80
100
120
5
5.5
6
6.5
7
7.5
8
Ambient Temperature (oC)
VVAD (V)
IFQ_AD vs. RIPRGM , or IFQ_USB vs. RIPUSB
IPQ_AD vs. RIPRGM , or IPQ_USB vs. RIPUSB
VVAD = 5V, VBAT = 3.7V, TA = 25οC
VVAD = 5V, VBAT = 2.6V, TA = 25οC
1000
800
600
400
200
0
200
160
120
80
40
0
2
6
10
14
18
22
26
30
2
6
10
14
18
22
26
30
Ω
Ω
)
RIPRGM or RIPUSB (k
)
RIPRGM or RIPUSB (k
CC — Input Reselection, AD to USB
CC — Input Reselection, USB to AD
V
BAT=3.7V, VVUSB=5.0V
V
BAT=3.7V, VVUSB=5.0V
V
VAD (1.0V/div)
VVAD (1.0V/div)
I
BAT (200mA/div)
IBAT (200mA/div)
VVAD=0V—
VVAD=0V—
I
BAT=0mA—
IBAT=0mA—
400μs/div
400μs/div
7
SC820
Typical Characteristics (continued)
Charging Cycle Battery Voltage and Current
Pre-Charging Battery Voltage and Current
850mAhr battery, RIPRGM = 2.94k , VVAD = 5.0V, TA = 25οC
850mAhr battery, RIPRGM = 2.94k , VVAD = 5.0V, TA = 25οC
Ω
Ω
4
3.75
3.5
3.25
3
800
700
600
500
400
300
200
100
0
7
6
5
4
3
2
1
0
700
600
500
400
300
200
100
0
IBAT
VBAT
VBAT
2.75
2.5
2.25
2
IBAT
0
2
4
6
8
10
12
14
16
18
20
0
0.25
0.5
0.75
1
1.25
1.5
1.75
2
2.25
Time (s)
Time (hrs)
CC-to-CV Battery Voltage and Current
Re-Charge Cycle Battery Voltage and Current
850mAhr battery, RIPRGM = 2.94k , VVAD = 5.0V, TA = 25οC
Ω
Ω
850mAhr battery, RIPRGM = 2.94k , VVAD = 5.0V, Load = 10mA
4.21
4.2
710
690
670
650
630
610
4.5
4
450
400
350
300
250
200
150
100
50
VBAT
IBAT
3.5
3
4.19
4.18
4.17
4.16
2.5
2
VBAT
1.5
1
IBAT
0.5
Discharge hours 2 - 6 omitted.
1.0 1.5 2/6
Time (hrs)
0
0
44
44.5
45
45.5
46
46.5
47
47.5
48
0.0
0.5
6.5
7.0
7.5
Time (min)
8
SC820
Pin Descriptions
Pin #
Pin Name
Pin Function
1
VAD
Supply pin — connect to charging adapter. This pin is protected against damage due to high voltage up to 30V.
Supply pin — connect to USB Vbus power. Typically 5V, limited load-current input. This pin is protected against
damage due to high voltage up to 30V.
2
VUSB
Status output pin — This open-drain pin is asserted (pulled low) when a valid charging supply is connected to
either VAD or VUSB, and a charging cycle begins. It is released when the termination current is reached, indicating
that charging is complete. STATB is not asserted for re-charge cycles.
3
4
5
STATB
GND
Ground
Fast-charge and pre-charge current programming pin for the VUSB power source — VUSB fast-charge current
is programmed by connecting a resistor from this pin to ground. VUSB pre-charge current is 20% of fast-charge
current.
IPUSB
Fast-charge and pre-charge current programming pin for the adapter power source — VAD fast-charge current
is programmed by connecting a resistor from this pin to ground. VAD pre-charge current is 20% of fast-charge
current. The charging termination threshold current (for either VAD or VUSB input selection) is 10% of the IPRGM
programmed fast-charge current.
6
IPRGM
7
8
BAT
ENB
Charger output — connect to battery positive terminal.
Combined device enable/disable — Logic high disables the device. Tie to GND to enable charging with indefinite
float-charging. Float this pin to enable charging without float-charge upon termination. Note that this pin must
be grounded if the SC820 is to be operated without a battery connected to BAT.
Pad is for heatsinking purposes — not connected internally. Connect exposed pad to ground plane using mul-
tiple vias.
T
Thermal Pad
9
SC820
Block Diagram
V_Adapter
USB_VBUS
1
2
VAD
VUSB
Regulated
System
Supply
Input Selection Logic
Ad/USB select
VVUSB_UV_LIM = 4.57V
To
System
Load
VCV = 4.2V
CV
BAT
7
CC
VIREF
Lithium-
Ion
Single
Cell
Battery
Pack
CC
Feedback
Selection
Die
Temperature
Thermal
Limiting
VT_CT
STATB
3
Pre-charge, CC/
CV & Termination
Controller, Logical
State Machine
Termination
VTIPRGM_TERM
VTENB_HIGH = ~1.50V
VTENB_LOW = ~0.55
Tri-level
Control
1V
ENB
IPUSB
RIPUSB
IPRGM
RIPRGM
GND
8
5
6
4
10
SC820
Applications Information
(VTReQ = 100mV typically). A re-charge cycle then begins
automatically and the process repeats. A forced re-charge
cycle can also be periodically commanded by the proces-
sor to keep the battery topped-off without float-charging.
See the Monitor State section for details. Re-charge cycles
are not indicated by the STATB pin.
Charger Operation
The SC820 is a dual-input stand-alone Li-ion battery
charger. The VAD input pin is optimized for a charging
adapter. The VUSB pin is optimized for charging from the
USB Vbus supply. The device is independently pro-
grammed for battery-capacity-dependent currents
(adapter fast-charge current and termination current)
using the IPRGM pin. Charging currents from the USB
Vbus supply, which has a maximum load specification,
are programmed using the IPUSB pin.
Charging Input Selection
The SC820 has two charging supply input pins. VAD is
optimized for adapter charging. VUSB is optimized for
charging from the USB Vbus power supply. The inputs
differ in selection rising and de-selection falling thresh-
olds, their behavior when overloading their respective
charging sources, and in which current programming pin
determines the fast-charge and pre-charge current. Both
use the same Over-Voltage Protection (OVP) threshold.
When a valid input supply is first detected, a charge cycle
is initiated and the STATB open-drain output goes low. If
the battery voltage is less than the pre-charge threshold
voltage, the pre-charge current is supplied. Pre-charge
current is 20% of the programmed fast-charge current for
the selected input.
Glitch filtering is performed on the VAD and VUSB inputs,
so an applied input voltage that is ringing across its selec-
tion threshold will not be selected until the ringing has
ceased. When both inputs exceed their respective UVLO
thresholds, VAD is selected even when VAD voltage is
applied while already charging from the VUSB input. VAD
is also selected in the case that the VAD voltage exceeds
its OVP threshold, so that an excessive VAD voltage will
disable charging despite the presence of a valid VUSB
input voltage.
When the battery voltage exceeds the pre-charge thresh-
old, typically within seconds for a standard battery with a
starting cell voltage greater than 2V, the fast-charge
Constant Current (CC) mode begins. The charge current
soft-starts in three steps (20%, 60%, and 100% of pro-
grammed fast-charge current) to reduce adapter load
transients. CC current is programmed by the IPRGM resis-
tance to ground when the VAD input is selected and by
the IPUSB resistance to ground when the VUSB input is
selected.
When a valid input (defined as greater than its selection
threshold and less than the OVP threshold) is first
selected, a charge cycle is initiated and the STATB output
is asserted. When a new input selection is made (when
VAD is applied or removed while VUSB is present), the
charge cycle is immediately halted and re-initiated with
the newly selected input. There is a momentary (approxi-
mately 1ms) interruption in output current and a release
and re-assertion of the STATB pin during input
res-election.
The charger begins Constant Voltage (CV) regulation
when the battery voltage rises to the fully-charged single-
cell Li-ion regulation voltage (VCV), nominally 4.2V. In CV
regulation, the output voltage is regulated, and as the
battery charges, the charge current gradually decreases.
The STATB output goes high when IBAT drops below the
termination threshold current, which is 10% of the IPRGM
pin programmed fast-charge current regardless of the
input selected. This is known as charge termination.
If the VAD input charging current loads the adapter
beyond its current limit, the VAD input voltage will be
pulled down to just above the battery voltage. This is
referred to as Current-Limited-Adapter (CLA) operation.
The adapter input de-selection falling threshold is set
close to the battery voltage pre-charge threshold to
permit low-dissipation charging from a current limited
adapter.
Optional Float-charging or Monitoring
Depending on the state of the ENB input, upon termina-
tion the SC820 either operates indefinitely as a voltage
regulator (float-charging) or it turns off its output. If the
output is turned off upon termination, the device enters
the monitor state. In this state, the output remains off until
the BAT pin voltage decreases by the re-charge threshold
11
SC820
Applications Information (continued)
The VUSB input provides a higher de-selection falling
threshold appropriate to the USB specification. The USB
input also provides Under-Voltage Load Regulation
(UVLR), in which the charging current is reduced if needed
to prevent overloading of the USB Vbus supply. UVLR can
serve as a low-cost alternative to directly programming
the USB low power charge current (by switching the
IPUSB resistor), or where there is no signal available to
indicate whether USB low or high power mode should be
selected.
9
,386% B 7\S
,
ꢁ
ꢀꢀꢁꢁꢁ ꢀ
)4 B 86%
5,386%
The nominal fast-charge current for either input can be
programmed to the minimum of 70mA (RIPxxx = 29.4kꢀ).
The maximum fast-charge current for the VAD input is
995mA nominally (RIPRGM = 2.05kꢀ), and for the VUSB
input, the programmed fast-charge current should not
exceed 450mA (RIPUSB = 4.42kꢀ) nominally. (If a greater
USB input fast-charge current is desired, please contact
your Semtech Field Applications Engineer for assistance.)
The VAD input is designed for lower dropout voltage at
high current, which ensures charging without thermal
limiting with a charging adapter operating in current limit
of at least 700mA.
Constant Current Mode Fast-charge Current
Programming
The Constant Current (CC) mode is active when the
battery voltage is above the pre-charge threshold voltage
(VTPreQ) and less than VCV. When VAD is the selected input,
the programmed CC regulation fast-charge (FQ) current
is inversely proportional to the IPRGM pin resistance to
GND according to the equation
Current regulation accuracy is dominated by gain error at
high current settings and offset error at low current set-
tings. The range of expected fast-charge output current
versus programming resistance RIPRGM or RIPUSB (for VAD or
VUSB input selected, respectively) is shown in Figures 1a
and 1b. The figures show the nominal current versus
nominal RIPRGM or RIPUSB resistance as the center plot and
two theoretical limit plots indicating maximum and
minimum current versus nominal programming resis-
tance. These plots are derived from models of the
expected worst-case contribution of error sources
depending on programmed current. The current range
9
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,
ꢁ
ꢀꢀꢁꢁꢁ ꢀ
)4 B $'
5,35*0
When VUSB is the selected input, the programmed CC
mode fast-charge current is inversely proportional to the
IPUSB pin resistance to GND according to the equation
1100
1050
1000
950
900
850
800
750
700
650
600
550
500
450
400
350
300
250
325
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5
5.5
6
6.5
7
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
Ω
RIPRGM or RIPUSB (k ), R-tol = 1%
Ω
RIPRGM or RIPUSB (k ), R-tol = 1%
Figure 1b — Fast-charge Current Tolerance versus
Programming Resistance, High Resistance Range
Figure 1a — Fast-charge Current Tolerance versus
Programming Resistance, Low Resistance Range
12
SC820
Applications Information (continued)
includes the uncertainty due to 1% tolerance resistors.
The dots on each plot indicate the currents obtained with
the Electronic Industries Association (EIA) E96 standard
value 1% tolerance resistors. Figures 1a and 1b show low
and high resistance ranges, respectively.
value 1% tolerance resistors. Figures 2a and 2b show low
and high resistance ranges, respectively.
Termination
When the battery voltage reaches VCV, the SC820 transi-
tions from constant current regulation to constant
voltage regulation. While VBAT is regulated to VCV, the
current into the battery decreases as the battery becomes
fully charged. When the output current drops below the
termination threshold current, charging terminates.
Upon termination, the STATB pin open drain output turns
off and the charger either enters monitor state or float-
charges the battery, depending on the logical state of the
ENB input pin.
Pre-charge Mode
This mode is automatically enabled when the battery
voltage is below the pre-charge threshold voltage (VTPreQ),
typically 2.9V. Pre-charge current conditions the battery
for fast charging. The pre-charge current value is fixed at
20% nominally of the fast-charge current for the selected
input. The fast-charge current is programmed by the
resistance between IPRGM and GND for the VAD input,
and by the resistance between IPUSB and GND for the
VUSB input.
The termination threshold current is fixed at 10% of the
VAD input fast-charge current, as programmed by the
resistance between IPRGM and GND. The IPRGM pin
resistance determines the termination threshold current
regardless of whether the selected charging input is VAD
or VUSB.
Pre-charge current regulation accuracy is dominated by
offset error. The range of expected pre-charge output
current versus programming resistance is shown in Figures
2a and 2b. The figures show the nominal pre-charge
current versus nominal resistance as the center plot and
two theoretical limit plots indicating maximum and
minimum current versus nominal programming resis-
tance. These plots are derived from models of the
expected worst-case contribution of error sources
depending on programmed current. The current range
includes the uncertainty due to 1% tolerance resistors.
The dots on each plot indicate the currents obtained with
the Electronic Industries Association (EIA) E96 standard
Charger output current is the sum of the battery charge
current and the system load current. Battery charge
current changes gradually, and establishes a slowly
diminishing lower bound on the output current while
charging in CV mode. The load current into a typical
digital system is highly transient in nature. Charge cycle
termination is detected when the sum of the battery
charging current and the greatest load current occurring
270
260
250
240
230
220
210
200
190
180
170
160
150
140
130
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90
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70
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30
0
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2.5
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4
4.5
5
5.5
6
6.5
7
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
Ω
Ω
RIPRGM or RIPUSB (k ), R-tol = 1%
RIPRGM or RIPUSB (k ), R-tol = 1%
Figure 2a — Pre-charge Current Tolerance versus
Programming Resistance, Low Resistance Range
Figure 2b — Pre-charge Current Tolerance versus
Programming Resistance, High Resistance Range
13
SC820
Applications Information (continued)
115
110
105
100
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
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0
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10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
2
2.5
3
3.5
4
4.5
5
5.5
6
6.5
7
Ω
RIPRGM (k ), R-tol = 1%
Ω
RIPRGM (k ), R-tol = 1%
Figure 3b — Termination Current Tolerance versus
Programming Resistance, High Resistance Range
Figure 3a — Termination Current Tolerance versus
Programming Resistance, Low Resistance Range
within the immediate 300ꢁs to 550ꢁs past interval is less
than the programmed termination current. This timing
behavior permits charge cycle termination to occur during
a brief low-load-current interval, and does not require that
the longer interval average load current be small.
• Charging enabled with float-charging disabled
and battery monitoring at termination (ENB =
mid range)
• Charging disabled (ENB = high range).
This input is designed to interface to a processor GPIO
port powered from a peripheral supply voltage as low as
1.8V or as high as a fully charged battery. While a con-
nected GPIO port is configured as an output, the proces-
sor writes a 0 to select ENB low-range, and 1 to select
high-range. The GPIO port is configured as an input to
select mid-range.
Termination threshold current accuracy is dominated by
offset error. The range of expected termination current
versus programming resistance RIPRGM (for either VAD or
VUSB input selected) is shown in Figures 3a and 3b. The
figures show the nominal termination current versus
nominal RIPRGM resistance as the center plot and two theo-
retical limit plots indicating maximum and minimum
current versus nominal programming resistance. These
plots are derived from models of the expected worst-case
contribution of error sources depending on programmed
current. The current range includes the uncertainty due
to a 1% tolerance resistor. The dots on each plot indicate
the currents obtained with the Electronic Industries
Association (EIA) E96 standard value 1% tolerance resis-
tors. Figures 3a and 3b show low and high resistance
ranges, respectively.
ENB can also be permanently grounded to select low-
range or left unconnected to select mid-range if it will not
be necessary to change the level selection.
The equivalent circuit looking into the ENB pin is a vari-
able resistance, minimum 15kꢀ, to an approximately 1V
source. The input will float to mid range whenever the
external driver sinks or sources less than 5μA, a common
worst-case characteristic of a high impedance or a weak
pull-up or pull-down GPIO configured as an input. The
driving GPIO must be able to sink at least 25μA or source
at least 50μA to ensure a low or high state, respectively.
(See the Electrical Characteristics table.)
Enable Input
The ENB pin is a tri-level logical input that allows selection
of the following behaviors:
With the ENB input voltage floating to mid-range, the
charger is enabled but it will turn off its output following
charge termination and will enter the monitor state. This
• Charging enabled with float-charging after ter-
mination (ENB = low range)
14
SC820
Applications Information (continued)
state is explained in the next section. Mid-range can be
selected either by floating the input (sourcing or sinking
less than 5ꢁA) or by being externally forced such that VENB
falls within the midrange limits specified in the Electrical
Characteristics table.
Monitor State
If the ENB pin is floating, the charger output and STATB pin
will turn off and the device will enter the monitor state
when a charge cycle is complete. If the battery voltage
falls below the re-charge threshold (VCV - VReQ) while in the
monitor state, the charger will automatically initiate a re-
charge cycle. The battery leakage current during monitor
state is no more than 1μA over temperature and typically
less than 0.1μA at room temperature.
While driven low (VENB < Max VIL), the charger is enabled
and will continue to float-charge the battery following
termination. If the charger is already in monitor state fol-
lowing a previous termination, it will exit the monitor state
and begin float-charging.
While in the monitor state, the ENB tri-level input pin
remains fully active, and although in midrange, is sensitive
to both high and low levels. The SC820 can be forced from
the monitor state (no float-charging) directly to float-
charging operation by driving ENB low. This operation will
turn on the charger output, but will not assert the STATB
output. If the ENB pin is again allowed to float to mid-
range, the charger will remain on only until the output
current becomes less than the termination current, and
charging terminates. The SC820 turns off its charging
output and returns to the monitor state within a millisec-
ond. This forced re-charge behavior is useful for periodi-
cally testing the battery state-of-charge and topping-off
the battery, without float-charging and without requiring
the battery to discharge to the automatic re-charge
voltage. ENB should be held low for at least 1ms to ensure
a successful forced re-charge.
While ENB is driven high (VENB > Min VIH), the charger is
disabled and the ENB input pin enters a high impedance
state, suspending tri-level functionality. The specified
high level input current IIH is required only until a high
level is recognized by the SC820 internal logic. The tri-
level float circuitry is then disabled and the ENB input
becomes high impedance. Once forced high, the ENB pin
will not float to mid range. To restore tri-level operation,
the ENB pin must first be pulled down to mid or low range
(at least to VENB < Max VIM), then, if desired, released (by
reconfiguring the GPIO as an input) to select mid-range. If
the ENB GPIO has a weak pull-down when configured as
an input, then it is unnecessary to drive ENB low to restore
tri-level operation; simply configure the GPIO as an input.
When the ENB selection changes from high-range to mid-
or low-range, a new charge cycle begins and STATB goes
low.
Forced re-charge can be requested at any time during the
charge cycle, or even with no charging source present,
with no detrimental effect on charger operation. This
allows the host processor to schedule a forced re-charge
at any desired interval, without regard to whether a charge
cycle is already in progress, or even whether a charging
source is present. Forced re-charge will neither assert nor
release the STATB output.
Note that if a GPIO with a weak pull-up input configura-
tion is used, its pull-up current will flow from the GPIO into
the ENB pin while it is floating to mid-range. Since the
GPIO is driving a 1V equivalent voltage source through a
resistance (looking into ENB), this current is small − possi-
bly less than 1μA. Nevertheless, this current is drawn from
the GPIO peripheral power supply and, therefore, from the
battery after termination. (See the next section, Monitor
State.) For this reason, it is preferable that the GPIO chosen
to operate the ENB pin should provide a true high imped-
ance (CMOS) configuration or a weak pull-down when
configured as an input. When pulled below the float
voltage, the ENB pin output current is sourced from VAD
or VUSB (the charging source), not from the battery.
Status Output
The STATB pin is an open-drain output. It is asserted
(driven low) as charging begins after a valid charging
source is connected and the voltage on either input is
between its selection and OVP limits. STATB is also
asserted as charging begins after the ENB input returns to
either of the enable voltage ranges (mid or low voltage)
from the disable range. STATB is subsequently released
when the termination current is reached to indicate end-
15
SC820
Applications Information (continued)
of-charge, when the ENB input is driven high to disable
charging, or when neither charging input is selected and
valid to charge. If the battery is already fully charged
when a charge cycle is initiated, STATB is asserted for
approximately 750μs before being released. The STATB
pin is not asserted for automatic re-charge cycles.
The logical transition from CC to CV results in the fastest
possible charging cycle that is compliant with the speci-
fied current and voltage limits of the Li-ion cell. The output
current is constant at the CC limit, then decreases abruptly
when the output voltage steps from the overshoot voltage
to the regulation voltage at the transition to CV control.
The STATB pin may be connected to an interrupt input to
notify a host controller of the charging status or it can be
used as an LED driver.
Thermal Limiting
Device thermal limiting is the third output constraint of
the Constant Current, Constant Voltage, “Constant”
Temperature (CC/CV/CT) control. This feature permits a
higher input OVP threshold, and thus the use of higher
voltage or poorly regulated adapters. If high input voltage
results in excessive power dissipation, the output current
is reduced to prevent overheating of the SC820. The
thermal limiting controller reduces the output current by
iT ≈ –50mA/ºC for any junction temperature TJ > TTL.
Logical CC-to-CV Transition
The SC820 differs from monolithic linear single cell Li-ion
chargers that implement a linear transition from CC to CV
regulation. The linear transition method uses two simul-
taneous feedback signals — output voltage and output
current — to the closed-loop controller. When the output
voltage is sufficiently below the CV regulation voltage, the
influence of the voltage feedback is negligible and the
output current is regulated to the desired current. As the
battery voltage approaches the CV regulation voltage
(4.2V), the voltage feedback signal begins to influence the
control loop, which causes the output current to decrease
although the output voltage has not reached 4.2V. The
output voltage limit dominates the controller when the
battery reaches 4.2V and eventually the controller is
entirely in CV regulation. The soft transition effectively
reduces the charge current below that which is permitted
for a portion of the charge cycle, which increases charge
time.
When thermal limiting is inactive,
TJ = TA + VΔ IFQ θJA,
where VΔ is the voltage difference between the VIN pin
and the BAT pin. However, if TJ computed this way exceeds
TTL, then thermal limiting will become active and the
thermal limiting regulation junction temperature will be
T
JTL = TA + VΔ I(TJTL) θJA,
where
I(TJTL) = IFQ + iT (TJTL − TTL).
In the SC820, a logical transition is implemented from CC
to CV to recover the charge current lost due to the soft
transition. The controller regulates only current until the
output voltage exceeds the transition threshold voltage.
It then switches to CV regulation. The transition voltage
from CC to CV regulation is typically 5mV higher than the
CV regulation voltage, which provides a sharp and clean
transition free of chatter between regulation modes. The
difference between the transition voltage and the regula-
tion voltage is termed the CC/CV overshoot. While in CV
regulation, the output current sense remains active. If the
output current exceeds by 5% the programmed fast-
charge current, the controller reverts to current
regulation.
(Note that iT is a negative quantity.) Combining these two
equations and solving for TJTL, the steady state junction
temperature during active thermal limiting is
TA ꢃ V'
IFQ_ x ꢂiT TTL
TJA
TJTL
1ꢂ V' iT TJA
Although the thermal limiting controller is able to reduce
output current to zero, this does not happen in practice.
Output current is reduced to I(TJTL), reducing power dissi-
pation such that die temperature equilibrium TJTL is
reached.
16
SC820
Applications Information (continued)
While thermal limiting is active, all charger functions
remain active and the charger logical state is preserved.
current, (IAD-LIM). In this configuration, the CC regulator will
operate with its pass device fully on (in saturation, also
called “dropout”). The voltage drop from VAD to BAT is
determined by the product of the minimum RDS-ON of the
pass device multiplied by the adapter supply current.
Operating a Charging Adapter in Current Limit
In high charging current applications, charger power dis-
sipation can be greatly reduced by operating the charging
adapter in current limit. The SC820 VAD input supports
adapter-current-limited charging with a low de-selection
falling threshold and with internal circuitry designed for
low input voltage operation. To operate an adapter in
current limit, RIPRGM is chosen such that the adapter input
programmed fast-charge current IFQ_AD exceeds the current
In dropout, the power dissipation in the SC820 is
PILIM = (minimum RDS-ON) x (IAD-LIM)2. Since minimum RDS-ON
does not vary with battery voltage, dropout power dissi-
pation is constant throughout the CC portion of the
charge cycle while the adapter remains in current limit.
The SC820 junction temperature will rise above ambient
by PILIM x θJA. If the device temperature rises to the tem-
perature at which the TL control loop limits charging
current (rather than the current being limited by the
adapter), the input voltage will rise to the adapter regula-
tion voltage. The power dissipation will increase so that
the TL regulation will further limit charge current. This will
keep the adapter in voltage regulation for the remainder
of the charge cycle. In this case, the SC820 will continue
to charge with thermal limiting until charge current
decreases while in CV regulation (reducing power dissipa-
tion sufficiently), resulting in a slow charge cycle, but with
no other negative effect.
limit of the charging adapter IAD-LIM
.
Note that if IAD-LIM is less than 20% of IFQ_AD, then the adapter
voltage can be pulled down to the battery voltage while
the battery voltage is below the pre-charge threshold. In
this case, care must be taken to ensure that the adapter
will maintain its current limit below 20% of IFQ_AD at least
until the battery voltage exceeds the pre-charge thresh-
old. Failure to do so could permit charge current to exceed
the pre-charge current while the battery voltage is below
the pre-charge threshold. This is because the low input
voltage will also compress the pre-charge threshold inter-
nal reference voltage to below the battery voltage. This
will prematurely advance the charger logic from pre-
charge current regulation to fast-charge regulation, and
the charge current will exceed the safe level recom-
mended for pre-charge conditioning.
To ensure that the adapter remains in current limit, the
internal device temperature must not rise to TTL. This
implies that θJA must be kept small enough, through
careful layout, to ensure that TJ = TA + (PILIM × θJA) < TTL.
The low de-selection falling threshold (VTADsel-F) permits
the adapter voltage to be pulled down to just above the
battery voltage by the charging load whenever the
adapter current limit is less than the programmed fast-
charge current. The SC820 should be operated with
adapter voltage below the rising selection threshold
(VTADSel-R) only if the low input voltage is the result of
adapter current limiting. This implies that the VAD voltage
first exceeds VTADsel-R to begin charging, and is subsequently
pulled down to just above the battery voltage by the
charging load.
VUSB Under-Voltage Load Regulation
VUSB pin UVLR prevents the battery charging current from
overloading the USB Vbus network, regardless of the pro-
grammed fast-charge value. When the VUSB input is
selected, the SC820 monitors the input voltage (VVUSB) and
reduces the charge current as necessary to keep VVUSB at or
above the UVLR limit of VUVLR = 4.57V typically. UVLR oper-
ates like a fourth output constraint (along with CC, CV, and
CT constraints), but it is active only when the VUSB input
is selected.
If the VUSB voltage is externally pulled below VUVLR while
the VAD input is absent, the UVLR feature will reduce the
charging current to zero. This condition will not be inter-
preted as termination and will not result in an end-of-
charge indication. The STATB pin will remain asserted as if
charging is continuing. This prevents repetitive indica-
Interaction of Thermal Limiting and Current Limited
Adapter Charging
To permit the charge current to be limited by the adapter,
it is necessary that the adapter input fast-charge current
be programmed greater than the maximum adapter
17
SC820
Applications Information (continued)
tions of end-of-charge alternating with start-of-charge in
the case that the external VUSB load is removed or is
intermittent.
conduction of heat from the die to the ambient environ-
ment. In this experiment, the final steady-state BAT
current was 462mA at TA = 25C on the SC820 evaluation
board. The fast thermal limiting feature ensures compli-
ance with CCSA YD/T 1591-2006, Telecommunication
Industrial Standard of the People’s Republic of China —
Technical Requirements and Test Method of Charger and
Interface for Mobile Telecommunication Terminal, Section
4.2.3.1.
Input Over-Voltage Protection
The VAD and VUSB input pins are protected from over-
voltage to at least 30V above GND. When the voltage of
the selected input exceeds the Over-Voltage Protection
(OVP) rising threshold (VTOVP-R), charging is halted. When
the input voltage falls below the OVP falling threshold
(VTOVP-F), charging resumes. Note that the VAD input
remains selected even in the case that the VAD voltage
exceeds the OVP threshold. An excessive VAD voltage will
disable charging despite the presence of a valid VUSB
voltage. An OVP fault turns off the STATB output. STATB is
turned on again when charging restarts.
Short Circuit Protection
The SC820 can tolerate a BAT pin short circuit to ground
indefinitely. The current into a ground short (while
VBAT < 1.8V) is approximately 10mA. For VBAT > 1.8V, normal
pre-charge current regulation is active.
A short circuit or too little programming resistance to
ground on the IPRGM pin (<< 2.05kΩ) or the IPUSB pin
(<< 4.42kΩ) will prevent proper regulation of the BAT pin
output current for the active programming pin. Prior to
enabling the output a check of the IPRGM and IPUSB pins
is performed to ensure that there is sufficient resistance to
ground. A test current is output on each programming
pin. If the test current produces a voltage of sufficient
amplitude on both programming pins, regardless of input
selected, then the output is enabled. An example with
The OVP threshold has been set relatively high to permit
the use of poorly regulated adapters. Such adapters may
output a high voltage until loaded by the charger. A
too-low OVP threshold could prevent the charger from
ever turning on and loading the adapter to a lower voltage.
If the adapter voltage remains high despite the charging
load, the fast thermal limiting feature will immediately
reduce the charging current to prevent overheating of the
SC820. This behavior is illustrated in Figure 4, in which VBAT
= 3.0V, IFQ = 700mA, and VVAD is stepped from 0V to 8.1V.
Initially, power dissipation in the SC820 is 3.6W.
R
IPRGM = 2.94kΩ is illustrated in Figure 5, in which the test
current is applied for approximately 250μs to determine
that there is no pin short. If a short on either program-
ming pin is detected, the test current persists until the
short to ground is removed, and then the charging startup
sequence will continue.
VVAD=8.1V, VBAT=3.0V
IBAT=700mA (Initially), PDISSIPATION=3.6W (Initially)
IBAT (100mA/div)
VVAD (2V/div)
VIPRGM (1V/div)
VBAT (2V/div)
VIPRGM=0V—
IBAT (500mA/div)
IBAT=0mA—
V
VAD ,VBAT=0V—
BAT=0mA—
I
1s/div
V
VIN (5V/div)
VVIN =0V—
Figure 4 — Thermal Limiting Example
400μs/div
Notice the BAT output current is rapidly reduced to limit
the internal die temperature, then continues to decline as
the circuit board gradually heats up, further reducing the
Figure 5 — IPRGM Pin Short-to-Ground Test During
Startup
18
SC820
Applications Information (continued)
During charging, a short to ground applied to the selected-
input active current programming pin (IPRGM or IPUSB) is
detected by a different mechanism, while a short to
ground on the inactive programming pin is ignored. Pin-
short detection on an active current programming pin
forces the SC820 into reset, turning off the output. A pin-
short on either programming pin will then prevent startup
regardless of the input selected. When the IPRGM and
IPUSB pin-short conditions are removed, the charger
begins normal operation automatically without input
power cycling.
will unnecessarily reduce charging current to 50mA, well
below the 100mA permitted.
An arbitrary ratio of USB low-to-high power charging cur-
rents can be obtained using an external n-channel FET
operated with a processor GPIO signal to engage a second
parallel IPUSB resistor. The external circuit is illustrated in
Figure 6.
IPUSB
5
RIPUSB_HI
USB Hi/Lo
Power Select
RIPUSB
Over-Current Protection
Over-current protection is provided in all modes of opera-
tion, including CV regulation. The output current is limited
to either the pre-charge or the fast-charge current (as
programmed by IPRGM or IPUSB, determined by input
selection), depending on the voltage at the output.
Figure 6 — External programming of arbitrary USB
high power and low power charge currents.
For USB low power mode charging, the external transistor
is turned off. The transistor is turned on when high power
mode is desired. The effect of the switched parallel IPUSB
resistor is to reduce the effective programming resistance
and thus raise the fast-charge current.
Operation Without a Battery
The SC820 can be operated as a 4.2V LDO regulator
without the battery present, for example, for factory
testing. If this use is anticipated, the total output capaci-
tance, CBAT plus any other capacitors tied directly to BAT
pin network, should be at least 2.2ꢁF but less than 22ꢁF to
ensure stability in CV regulation. To operate the charger
without a battery, the ENB pin must be driven low or
grounded. The output current is limited by the pro-
grammed fast-charge current for the selected input. The
charger should not be disabled (VENB > VIH) without a
battery present.
An open-drain GPIO can be used directly to engage the
parallel resistor RIPUSB_HI. Care must be taken to ensure that
the RDS-ON of the GPIO is considered in the selection of
R
IPUSB_HI. Also important is the part-to-part and tempera-
ture variation of the GPIO RDS-ON, and their contribution to
the USB High Power charge current tolerance. Note also
that IPUSB will be pulled up briefly to as high as 3V during
startup to check for an IPUSB static pinshort to ground. A
small amount of current could, potentially, flow from
IPUSB into the GPIO ESD structure through RIPUSB_HI during
this event. While unlikely to do any harm, this effect must
also be considered.
Design Considerations — USB Charging
The USB specification restricts the load on the USB Vbus
power network to 100mA for low power devices and for
high power devices prior to granting permission for high
power operation. The specification restricts the Vbus load
to 500mA for high power devices after granting permis-
sion to operate as a high power device. This suggests that
a fixed 1:5 ratio of low power to high power charging
current is desirable. But this can result in suboptimal
charging when the battery capacity is too small to permit
fast charging at 500mA. For example, a 250mAh battery
will typically require a fast-charge current of 250mA or
less. A fixed 1:5 ratio for USB low and high power charging
For purposes of design for dual-input adapter/USB charg-
ing, a small battery is one with a desired fast-charge
current less than 500mA. A 300mAh battery with
maximum fast-charge current of 300mA is an example.
The adapter input and USB input high power fast-charge
currents should both be set to 300mA maximum. The USB
input low power fast-charge current is 100mA maximum.
Refer to the circuit of Figure 4 and the data of Figures 1a
and 1b. For IFQ_AD = 300mA maximum, use RIPRGM = 7.50kΩ.
The fixed IPUSB resistor of RIPUSB = 23.2kΩ programs IFQ_USB
19
SC820
Applications Information (continued)
= 100mA maximum. When parallel resistor RIPUSB_HI
11.0kΩ is switched in, the equivalent IPUSB resistor is
7.50kΩ, and so IFQ_USB = 300mA maximum.
=
Capacitor Selection
Low cost, low ESR ceramic capacitors such as the X5R and
X7R dielectric material types are recommended. The BAT
pin capacitor should be at least 1ꢁF, but can be as large as
desired to accommodate the required input capacitors of
regulators connected directly to the battery terminal. BAT
pin total capacitance must be limited if the SC820 is to be
operated without the battery present. See the section
Operation Without a Battery. The VAD pin and VUSB pin
capacitors are typically between 0.1ꢁF and 2.2ꢁF, although
larger values will not degrade performance. Capacitance
must be evaluated at the expected bias voltage (4.2V for
the BAT pin capacitor, the expected VVAD and VVUSB supply
regulation voltages for the input pin capacitors), rather
than the zero-volt capacitance rating.
A large battery is any battery with a desired fast-charge
current exceeding 500mA. Large battery charging is most
consistent with the USB fixed 1:5 current ratio low-to-high
power model of operation. For example, consider an
800mAh battery, with maximum fast-charge current of
800mA. The adapter input fast-charge should be config-
ured for 800mA maximum (RIPRGM = 2.80kΩ), the USB low
power fast-charge set to 100mA max (RIPUSB = 23.2kΩ), and
the USB high power fast-charge set to 500mA maximum
(RIPUSB_HI = 5.62kΩ).
USB Low Power Mode Alternative
Where a USB mode selection signal is not available, or
where system cost or board space make USB low power
mode external current programming impractical, USB low
power charging can be supported indirectly. The IPUSB
pin resistance can be selected to obtain the desired USB
high power charge current. The VUSB pin UVLR feature
ensures that the charging load will never pull the USB
Vbus supply voltage below VUVLR regardless of the USB
host or hub supply limit. The UVLR limit voltage guaran-
tees that the voltage of the USB Vbus supply will not be
loaded below the low power voltage specification limit, as
seen by any other low power devices connected to the
same USB host or hub.
PCB Layout Considerations
Layout for linear devices is not as critical as for a switching
regulator. However, careful attention to detail will ensure
reliable operation.
• Place input and output capacitors close to the
device for optimal transient response and device
behavior.
• Connect all ground connections directly to the
ground plane. If there is no ground plane,
connect to a common local ground point before
connecting to board ground near the GND pin.
• Attaching the part to a larger copper footprint
will enable better heat transfer from the device,
especially on PCBs with internal ground and
power planes.
20
SC820
Outline Drawing — MLPD-UT8 2x2
B
E
A
D
DIMENSIONS
INCHES MILLIMETERS
MIN NOM MAX MIN NOM MAX
DIM
-
-
-
A
A1
A2
b
.020
.000
.024 0.50
.002 0.00
0.60
0.05
PIN 1
INDICATOR
(LASER MARK)
-
(.006)
(0.1524)
.007
0.25 0.30
.010 .012 0.18
D
D1
E
E1
e
.075 .079 .083 1.90 2.00 2.10
.061 .067 .071 1.55 1.70 1.80
.075
.026 .031 .035 0.65 0.80 0.90
.020 BSC
0.50 BSC
.079
.083 1.90 2.00 2.10
A
C
SEATING
PLANE
L
N
aaa
.012 .014 .016 0.30
0.40
0.35
8
0.08
0.10
aaa
C
8
.003
.004
A2
A1
bbb
D1
1
2
LxN
E/2
E1
N
bxN
bbb
C A B
e
e/2
D/2
NOTES:
1.
2.
CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS THE TERMINALS.
21
SC820
Land Pattern — MLPD-UT8 2x2
H
DIMENSIONS
INCHES
R
DIM
MILLIMETERS
(.077)
.047
.067
.031
.020
.006
.012
.030
.106
(1.95)
1.20
1.70
0.80
0.50
0.15
0.30
0.75
2.70
C
G
H
K
P
R
X
Y
Z
Z
(C)
K
G
Y
P
X
NOTES:
1.
2.
CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY.
CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR
COMPANY'S MANUFACTURING GUIDELINES ARE MET.
THERMAL VIAS IN THE LAND PATTERN OF THE EXPOSED PAD
SHALL BE CONNECTED TO A SYSTEM GROUND PLANE.
FAILURE TO DO SO MAY COMPROMISE THE THERMAL AND/OR
FUNCTIONAL PERFORMANCE OF THE DEVICE.
3.
Contact Information
Semtech Corporation
Power Management Products Division
200 Flynn Road, Camarillo, CA 93012
Phone: (805) 498-2111 Fax: (805) 498-3804
www.semtech.com
22
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