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PDF LTC3822-1 Data sheet ( Hoja de datos )
| Número de pieza | LTC3822-1 | |
| Descripción | Synchronous Step-Down DC/DC Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3822-1
FEATURESwww.datasheet4u.com
No RSENSETM, Low Input
Voltage, Synchronous
Step-Down DC/DC Controller
DESCRIPTION
■ Dual N-Channel MOSFET Synchronous Drive
■ No Current Sense Resistor Required
■ Optimized for 3.3VIN and Li-Ion Applications
■ Constant Frequency Current Mode Operation for
Excellent Line and Load Transient Response
■ ±1% 0.6V Reference
■ Low Dropout Operation: 99% Duty Cycle
■ Phase-Lockable or Adjustable Frequency:
250kHz to 750kHz
■ Internal Soft-Start Circuitry
■ Tracking and Adjustable Soft-Start Input
■ Selectable Maximum Peak Current Sense Threshold
■ Selectable Burst Mode®/ Forced Continuous/Pulse
Skipping Mode at Light Load
■ Digital RUN Control Pin
■ Output Overvoltage Protection
■ Micropower Shutdown: IQ = 7.5µA
■ Tiny Thermally Enhanced 12-Pin (3mm × 3mm) DFN
or 16-Pin Narrow SSOP Packages
APPLICATIONS
■ Single Cell Li-Ion Powered Systems
■ 3.3VIN Systems
, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology
Corporation. No RSENSE is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by Patents, including 5481178, 5929620, 6580258, 6304066, 5847554,
6611131, 6498466, 5705919.
The LTC®3822-1 is a synchronous step-down switching
regulator controller that drives external N-channel power
MOSFETs using few external components. The constant
frequency current mode architecture with MOSFET VDS
sensing eliminates the need for sense resistors and im-
proves efficiency.
Burst Mode operation provides high efficiency at light
loads. The 99% maximum duty cycle provides low dropout
operation, extending operating time in battery-powered
systems.
The operating frequency can be programmed up to 750kHz,
allowing the use of small surface mount inductors and ca-
pacitors. For noise sensitive applications, the LTC3822-1
can be synchronized to an external clock from 250kHz to
750kHz.
The LTC3822-1 is available in the tiny footprint thermally
enhanced 12-pin DFN package or 16-pin narrow SSOP
package.
LTC3822-1
LTC3822
Light Load
Operation
Continuous, Discontinuous Discontinuous Mode
or Burst Mode Operation
Package
DD12 (3mm × 3mm), GN16 DD10 (3mm × 3mm),
MS10E
Tracking/Soft-Start Yes
Internal Soft-Start Only
External Sync
Yes
No
PGOOD Pin
GN16 Only
No
TYPICAL APPLICATION
10.2k
1nF
IPRG
RUN
VIN
PLLLPF TG
LTC3822-1
ITH SW
BOOST
SYNC/MODE
TRACK/SS
GND BG
VFB GND
59k 118k
0.47µH
0.1µF
47µF
×2
VIN
3.3V
47µF
×2
VOUT
1.8V
8A
38221 TA01
Efficiency/Power Loss vs Load Current
100 10
90
Burst Mode
80 EFFICIENCY
70
1
60
50
40
30
20
10
0
10
Burst Mode
POWER LOSS
0.1
0.01
VIN = 3.3V
VOUT = 1.8V
FIGURE 10 CIRCUIT 0.001
100
1000
10000
LOAD CURRENT (mA) 38221 TA01b
38221f
1
1 page  
LTC3822-1
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise noted.
Oscillator Frequency
vs Input Voltage
www.data5sheet4u.com
4
3
2
1
0
–1
–2
–3
–4
–5
2.5
3.0 3.5 4.0
INPUT VOLTAGE (V)
4.5
38221 G11
Quiescent Current in Normal
Operation vs Input Voltage
390
380
370
360
350
340
330
2.5
3.0 3.5 4.0
INPUT VOLTAGE (V)
4.5
3822 G13
Maximum Current Sense Voltage
vs ITH Pin Voltage
100
Burst Mode OPERATION
(ITH RISING)
80 Burst Mode OPERATION
(ITH FALLING)
FORCED CONTINUOUS
60 MODE
PULSE SKIPPING
40 MODE
20
0
–20
0.5
1 1.5
ITH VOLTAGE (V)
2
38221 G03
Start-Up with Internal Soft-Start
Shutdown Quiescent Current
vs Input Voltage
18
16
14
12
10
8
6
4
2
0
2.5 3.0 3.5 4.0 4.5
INPUT VOLTAGE (V)
38221 G12
Start-Up with External Soft-Start
Capacitor
VRUN
1V/DIV
VOUT
1V/DIV
VRUN
1V/DIV
VTRACK/SS
1V/DIV
VOUT
1V/DIV
200µs/DIV
FIGURE 10 CIRCUIT
VIN = 3.3V
VOUT = 1.8V
RLOAD = 1.5Ω
38221 G14
4ms/DIV
FIGURE 10 CIRCUIT
VIN = 3.3V
VOUT = 1.8V
RLOAD = 1.5Ω
CSS = 0.01µF
38221 G15
Soft-Start with Tracking
Continuous Mode Operation
VTRACK/SS
500mV/DIV
VOUT
1V/DIV
4ms/DIV
FIGURE 10 CIRCUIT
VIN = 3.3V
VOUT = 1.8V
RLOAD = 1.5Ω
38221 G16
VSW
2V/DIV
VOUT
20mV/DIV
AC COUPLED
IL
2A/DIV
2µs/DIV
FIGURE 10 CIRCUIT
VIN = 3.3V
VOUT = 1.8V, 100mA
38221 G17
38221f
5
5 Page 
LTC3822-1
OPERATION (Refer to Functional Diagram)
Undervoltage Lockout
To prevent operation of the MOSFETs below safe input
wwwv.doalttaasgheeelt4euv.ecolsm, an undervoltage lockout is incorporated
in the LTC3822-1. When the input supply voltage (VIN)
drops below 2.25V, the external MOSFETs and all internal
circuits are turned off except for the undervoltage block,
which draws only a few microamperes.
Peak Current Sense Voltage Selection and Slope
Compensation (IPRG Pin)
When the LTC3822-1 controller is operating below 20%
duty cycle, the peak current sense voltage (between the
VIN and SENSE–/SW pins) allowed across the external top
MOSFET is determined by:
∆VSENSE(MAX)
≈
A
•
VITH
– 0.7V
10
where A is a constant determined by the state of the IPRG
pin. Floating the IPRG pin selects A = 1; tying IPRG to
VIN selects A = 5/3; tying IPRG to GND selects A = 2/3.
The maximum value of VITH is typically about 1.98V, so
the maximum sense voltage allowed across the external
main MOSFET is 125mV, 200mV or 82mV for the three
respective states of the IPRG pin.
However, once the controller’s duty cycle exceeds 20%,
slope compensation begins and effectively reduces the
peak sense voltage by a scale factor (SF) given by the
curve in Figure 1.
The peak inductor current is determined by the peak sense
voltage and the on-resistance of the main MOSFET:
IPK
=
∆VSENSE(MAX)
RDS(ON)
If a sense resistor is used, ΔVSENSE(MAX) is the peak cur-
rent sense voltage (between the VIN and SENSE–/SW pins)
across the sense resistor. The peak inductor is determined
by the peak sense voltage and the resistance of the sense
resistor:
IPK
=
∆VSENSE(MAX)
RSENSE
Power Good (PGOOD) Pin (GN Only)
A window comparator monitors the feedback voltage and
pulls the open-drain PGOOD output pin low when the
feedback voltage is not within ±10% of the 0.6V reference
voltage. PGOOD is low when the LTC3822-1 is shut down
or in undervoltage lockout.
110
100
90
80
70
60
50
40
30
20
10
0
0 10 20 30 40 50 60 70 80 90 100
DUTY CYCLE (%)
38221 F01
Figure 1. Maximum Peak Current vs Duty Cycle
38221f
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LTC3822-1.PDF ] | |
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